CN118041381A

CN118041381A - Frequency modulation broadcast circuit and electronic equipment

Info

Publication number: CN118041381A
Application number: CN202410238836.9A
Authority: CN
Inventors: 蔡昭晨; 黄宗伟; 高伟
Original assignee: Honor Device Co Ltd
Current assignee: Honor Device Co Ltd
Priority date: 2024-03-04
Filing date: 2024-03-04
Publication date: 2024-05-14

Abstract

The application provides a frequency modulation broadcasting circuit and electronic equipment, which can filter out high-frequency noise overlapped with an FM frequency band on an FM antenna of a TYPE-C digital earphone and improve the quality of FM signals. The ground wire connecting end of the frequency modulation broadcasting circuit is respectively connected with one end of the first pass FM filter unit and one end of the resistance FM filter unit, the protocol signal connecting end is connected with one end of the second pass FM filter unit, the other end of the first pass FM filter unit and the other end of the second pass FM filter unit are respectively connected with the input end of the noise processing unit, and the other end of the resistance FM filter unit is grounded; the second through FM filter unit transmits interference signals in an FM frequency band generated when the protocol signal connection terminal receives the protocol signals to the noise processing unit; the first pass FM filter unit transmits FM signals picked up by the ground wire of the TYPE-C digital earphone received by the ground wire connecting end to the noise processing unit, wherein the FM signals comprise useful FM signals and interference signals; the noise processing unit is used for processing the FM signal and the interference signal to obtain a useful FM signal.

Description

Frequency modulation broadcast circuit and electronic equipment

Technical Field

The present application relates to the field of communications technologies, and in particular, to a frequency modulation broadcast circuit and an electronic device.

Background

In electronic devices such as mobile phones, a frequency modulation broadcast (Frequency Modulation, abbreviated as FM) function is generally integrated. An antenna with a corresponding length is needed for receiving the FM signals, but electronic equipment such as a mobile phone and the like usually does not have an built-in FM antenna, but takes the electronic equipment as the FM antenna by means of an earphone wire, and a corresponding FM circuit is arranged in the electronic equipment to realize the FM function.

Currently, FM circuits are mostly designed for 3.5mm headphones and analog headphones that employ a universal serial bus (Universal Serial Bus, USB) TYPE-C interface. However, with the gradual evolution of electronic devices such as mobile phones, digital headphones of TYPE-C interface are gradually replacing traditional 3.5mm headphones and analog headphones of TYPE-C interface. When the digital earphone of the TYPE-C interface is used as an FM antenna, how to set an FM circuit to better realize the FM function is an urgent problem to be solved.

Disclosure of Invention

In order to solve the technical problems, the application provides a frequency modulation broadcasting circuit and electronic equipment, which can better realize the FM function when a digital earphone with a TYPE-C interface is used as an FM antenna.

In a first aspect, an embodiment of the present application provides a FM broadcast circuit for implementing an FM function in cooperation with a digital earphone of a TYPE-C interface, the FM broadcast circuit including: the system comprises a ground wire connection end, a protocol signal connection end, an output connection end, a first pass FM filter unit, a second pass FM filter unit, a resistance FM filter unit, a noise processing unit and an FM signal demodulation chip; the ground wire connecting end is respectively connected with one end of the first pass FM filter unit and one end of the resistance FM filter unit, the protocol signal connecting end is connected with one end of the second pass FM filter unit, the other end of the first pass FM filter unit and the other end of the second pass FM filter unit are respectively connected with the input end of the noise processing unit, the other end of the resistance FM filter unit is grounded, and the FM signal demodulation chip is respectively connected with the output end and the output connecting end of the noise processing unit; the second through FM filter unit is used for transmitting interference signals in an FM frequency band generated when the protocol signal connection end transmits the protocol signals to the noise processing unit; the first pass FM filter unit is used for transmitting the FM signal picked up by the ground wire of the TYPE-C digital earphone received by the ground wire connecting end to the noise processing unit, wherein the FM signal transmitted by the first pass FM filter unit comprises a useful FM signal and an interference signal in an FM frequency band; the noise processing unit is used for processing the FM signal and the interference signal in the FM frequency band to obtain a useful FM signal; the FM signal demodulation chip is used for demodulating useful FM signals into FM data and outputting the FM data through the output connection terminal.

The noise processing unit is used for filtering interference signals in the FM frequency band, so that the problem that the FM function cannot be better realized due to larger noise on the ground wire when the ground wire of the TYPE-C digital earphone is used as an FM antenna to realize the FM function is avoided, the FM circuit performance of the TYPE-C digital earphone is optimized, the quality of the FM signals is improved, the user experience is improved, and the use scene of the digital earphone of the TYPE-C interface of a user is increased.

The protocol signal connection terminal may include one connection terminal, two connection terminals, more connection terminals, and the like.

Illustratively, the interfering signal in the FM band includes a high frequency component of the protocol signal.

Illustratively, the blocking FM filter unit includes a blocking FM filter in the following.

According to a first aspect, the protocol signal connection comprises a first protocol signal connection and a second protocol signal connection; the first pass FM filter unit comprises a first pass FM filter, and the second pass FM filter unit comprises a second pass FM filter and a third pass FM filter; the ground wire connecting end is connected with one end of the first pass FM filter, the first protocol signal connecting end is connected with one end of the second pass FM filter, the second protocol signal connecting end is connected with one end of the third pass FM filter, and the other end of the first pass FM filter, the other end of the second pass FM filter and the other end of the third pass FM filter are respectively connected with the input end of the noise processing unit; the second through FM filter is used for transmitting interference signals in an FM frequency band generated when the first protocol signal connecting end receives the protocol signals to the noise processing unit; the third three-way FM filter is used for transmitting interference signals in an FM frequency band generated when the second protocol signal connecting end receives the protocol signals to the noise processing unit; the first pass FM filter unit is used for transmitting the FM signal picked up by the ground wire of the TYPE-C digital earphone received by the ground wire connecting end to the noise processing unit, wherein the FM signal transmitted by the first pass FM filter unit comprises a useful FM signal and an interference signal in an FM frequency band.

When the electronic equipment needs protocol interaction through the two connecting ends, by setting a corresponding FM filter for each protocol signal connecting end, high-frequency components of USB protocol signals at each protocol signal connecting end are transmitted to the noise processing unit, and interference signals in FM frequency bands in FM signals are filtered through the noise processing unit, so that the application range of the FM broadcasting circuit is enlarged.

Of course, the protocol signal connection terminal may also include only one protocol signal connection terminal; or include more protocol signal connections.

According to the first aspect, or any implementation manner of the first aspect, the first, second and third pass FM filters have the same structure.

The setting like this for the scope of the signal that every logical FM wave filter passed through is the same, and like this, noise processing unit obtains useful FM signal more accurate, further improves FM signal quality, promotes user experience.

According to the first aspect, or any implementation manner of the first aspect, the noise processing unit includes a first input end, a second input end, a third input end, an output end, a first input resistor unit, a second input resistor unit, a third input resistor unit, a fourth input resistor unit, a feedback resistor unit and an operational amplifier, one end of the first input resistor unit is connected with the third input end, one end of the second input resistor unit is connected with the second input end, one end of the third input resistor unit is connected with the first input end, the other end of the first input resistor unit is connected with one end of the feedback resistor unit, the other end of the second input resistor unit and an inverting end of the operational amplifier respectively, the other end of the feedback resistor unit is connected with the output end of the noise processing unit and the output end of the operational amplifier respectively, the other end of the third input resistor unit is connected with one end of the fourth input resistor unit and the same-phase end of the operational amplifier respectively, and the other end of the fourth input resistor unit is grounded. I.e. the noise processing unit is simple in structure.

According to the first aspect, or any implementation manner of the first aspect, the resistance value of the feedback resistor unit is far greater than the resistance value of the first input resistor unit and the second input resistor unit after being connected in parallel; and/or the resistance of the first input resistance unit is far greater than the resistance of the fourth input resistance unit.

According to the first aspect, or any implementation manner of the first aspect above, the voltage Vout at the output of the noise processing unit satisfies: vout=rf (Vin 1/R1-Vin3/R3-Vin 2/R2); wherein Vin3 is the voltage of the interference signal in the FM frequency band propagated by the third pass FM filter, vin2 is the voltage of the interference signal in the FM frequency band propagated by the second pass FM filter, vin1 is the voltage of the useful FM signal propagated by the first pass FM filter and the interference signal in the FM frequency band, rf is the resistance of the feedback resistor unit, R1 is the resistance of the first input resistor unit, R2 is the resistance of the second input resistor unit, and R3 is the resistance of the third input resistor unit.

According to a first aspect, or any implementation of the first aspect above, the first, second and/or third pass FM filters comprise band pass filters. The band-pass filter may be an 80-100 mhz band-pass filter, for example.

In a second aspect, an embodiment of the present application provides an electronic device, where the electronic device includes an external interface, a processing module, and the fm broadcast circuit corresponding to any one implementation manner of the first aspect; the external interface comprises a grounding pin and a protocol pin; the ground wire connecting end of the frequency modulation broadcasting circuit is connected with the grounding pin of the external interface, the protocol signal connecting end of the frequency modulation broadcasting circuit is respectively connected with the protocol pin of the external interface and the processing module, and the output connecting end of the frequency modulation broadcasting circuit is connected with the processing module; when the TYPE-C digital earphone is inserted into the external interface, the processing module is used for transmitting protocol signals with the TYPE-C digital earphone through the protocol signal connecting end of the frequency modulation broadcasting circuit and the protocol pin of the external interface so as to perform protocol interaction; and the receiving antenna is also used for processing the FM data output by the output connection end so as to enable the TYPE-C digital earphone to be used as a receiving antenna of an FM signal to realize an FM function.

Any implementation manner of the second aspect and the second aspect corresponds to any implementation manner of the first aspect and the first aspect, respectively. The technical effects corresponding to the second aspect and any implementation manner of the second aspect may be referred to the technical effects corresponding to the first aspect and any implementation manner of the first aspect, which are not described herein.

According to a second aspect, the external interface comprises a USB Type-C interface or the like.

According to a second aspect, or any implementation manner of the above second aspect, the protocol signal connection terminal includes a first protocol signal connection terminal and a second protocol signal connection terminal; the first protocol signal connection end is a D-pin of the USB Type-C interface, and the second protocol signal connection end is a D+ pin of the USB Type-C interface.

Of course, the first protocol signal connection end and the second protocol signal connection end may also be other pins of the USB Type-C interface, and specific pins may be selected according to practical situations.

Drawings

Fig. 1 is a schematic structural diagram of an electronic system according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a structure of a digital earphone;

FIG. 3 is a schematic diagram of the USB Type-C interface;

FIG. 4 is a circuit diagram of an electronic device;

fig. 5 is a circuit diagram of an electronic device according to an embodiment of the present application;

fig. 6 is a circuit diagram of a noise processing unit according to an embodiment of the present application.

Detailed Description

The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

The term "and/or" is herein merely an association relationship describing an associated object, meaning that there may be three relationships, e.g., a and/or B, may represent: a exists alone, A and B exist together, and B exists alone.

The terms first and second and the like in the description and in the claims of embodiments of the application, are used for distinguishing between different objects and not necessarily for describing a particular sequential order of objects. For example, the first target object and the second target object, etc., are used to distinguish between different target objects, and are not used to describe a particular order of target objects.

In embodiments of the application, words such as "exemplary" or "such as" are used to mean serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" or "e.g." in an embodiment should not be taken as preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "such as" is intended to present related concepts in a concrete fashion.

In the description of the embodiments of the present application, unless otherwise indicated, the meaning of "a plurality" means two or more. For example, the plurality of processing units refers to two or more processing units; the plurality of systems means two or more systems.

In the description of embodiments of the present application, unless explicitly stated and limited otherwise, the term "coupled" is to be interpreted broadly, as for example, whether fixedly coupled, detachably coupled, or integrally coupled; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the embodiments of the present application will be understood by those of ordinary skill in the art according to specific circumstances.

The frequency modulation (Frequency Modulation, FM) function of an electronic device (such as a mobile phone) is an important function for many users, and the users can listen to broadcast signals through the FM function of the mobile phone to obtain external information. In practice, the electronic device needs to be provided with an FM antenna, and an FM analog signal is picked up by the FM antenna, and then the FM analog signal can be sent to an FM circuit to be demodulated into FM data, and then the FM data is sent to a System On Chip (SOC) end for processing, and finally sent to a user for listening. However, in general, an electronic device such as a mobile phone does not have an FM antenna built therein, but uses an earphone cord as an FM antenna to realize an FM function.

Currently, the most common headphones include 3.5mm headphones and TYPE-C interface headphones, wherein TYPE-C interface headphones include TYPE-C interface analog headphones and TYPE-C interface digital headphones. Because the digital earphone of the TYPE-C interface has the advantages of better tone quality and the like, the traditional 3.5mm earphone and the analog earphone of the TYPE-C interface are gradually replaced.

Next, when a digital earphone (hereinafter referred to as a TYPE-C digital earphone) of a TYPE-C interface is used as an FM antenna, a scheme in which the TYPE-C digital earphone is matched with an FM circuit of an electronic device to realize an FM function will be described.

Referring to fig. 1, fig. 1 is a schematic structural diagram of an electronic system according to an embodiment of the present application. As shown in fig. 1, an electronic system 01 provided in the embodiment of the present application includes an earphone 10 and an electronic device 20, where the earphone 10 is a digital earphone, and the electronic device 20 may be a mobile phone, a computer, a tablet computer, a personal digital assistant (PDA for short), a vehicle-mounted computer, a television, an intelligent wearable device, an intelligent home device, etc., and the embodiment of the present application does not particularly limit a specific form of the electronic device 20, and the embodiment of the present application is illustrated by taking the electronic device 20 as an example of the mobile phone.

The side of the electronic device 20 is provided with an external interface (e.g. a USB TYPE-C interface, which may be referred to as a first TYPE-C interface for distinction) 21, and the external interface 21 may be used as a charging interface or an earphone interface. Referring to fig. 2, fig. 2 is a schematic structural diagram of a digital earphone, where the TYPE-C digital earphone includes an external interface (e.g., a USB TYPE-C interface, for distinction, may be referred to as a second TYPE-C interface) 11, the second TYPE-C interface 11 of the TYPE-C digital earphone corresponds to the external interface 21 of the electronic device 20, and the second TYPE-C interface 11 of the TYPE-C digital earphone may be directly inserted into the external interface 21 of the electronic device 20 to receive a phone, play music, etc. through the TYPE-C digital earphone, and an FM function is implemented through the FM circuit cooperation of the TYPE-C digital earphone and the electronic device.

Referring to fig. 3, fig. 3 is a schematic structural diagram of the USB Type-C interface. As shown in fig. 3, the USB Type-C interface (USB class C interface defined by the USB association) may use any USB transmission protocol, such as USB 2.0 protocol, USB 3.0 protocol or USB 3.1 protocol, to support functions of charging, data transmission, display output, and the like of the USB standard. The USB Type-C interface does not distinguish between front and back sides (i.e., a-side and B-side), and is an interface that supports double-sided insertion. The A face and the B face of the USB Type-C interface comprise: 4 VBUS pins for power, 4 GND pins for ground (ground pins), two CC pins (CC 1 pin and CC2 pin), 4 pairs of TX pins and RX pins, 2 pairs of D+ (also may be referred to as DP or data positive signal) pins and D- (also may be referred to as DM or data negative signal) pins, and a pair of SBU pins (SBU 1 pin and SBU2 pin).

Wherein the VBUS pin and the GND pin are return paths for power and signals. The CC pins may be used to determine whether the direction of device insertion is forward or reverse, determine different peripheral types by detecting different resistance values of the peripheral, configure different modes, and so on. The D+ pin and the D-pin are used for transmitting data and being compatible with other USB standards, and can be connected with a main chip of a main board of a mobile phone and other equipment. The TX pin and the RX pin are differential data transmission pins for data transmission. The SBU1 pins and the SBU2 pins are auxiliary pins, and have different applications in different application scenarios, and this embodiment will not be described in detail.

Referring to fig. 4, fig. 4 is a circuit diagram of an electronic device, and as shown in fig. 4, the electronic device 20 includes an external interface 21, an FM circuit 22, and a processing module 23. The external interface 21 is a USB Type-C interface. The processing module 23 may be a processing chip with a processing function, such as a System On Chip (SOC) chip or a power management chip (power management unit, PMU) of the electronic device 20, which is not limited in the present application. The d+ pin and the D-pin of the external interface 21 are electrically connected to the processing module 23, and when the external device is inserted into the external interface 21, the d+ pin and the D-pin of the external device are connected to the d+ pin and the D-pin of the electronic device 20, and the processing module 23 (which may be integrated with a USB protocol chip inside) may perform USB protocol interaction (transmit a USB protocol signal, that is, USB data) with the external device (which may be internally provided with a USB protocol chip that may perform protocol interaction with a USB protocol chip in the processing module 23) through the d+ pin and the D-pin, so as to determine a type of the external device at the external interface 21, such as a digital earphone, an analog earphone, or a USB connection line.

It should be noted here that, in the electronic device 20, a USB protocol chip for performing USB protocol interaction may be integrated into the processing module 23, or may be separately provided, which is not limited by the embodiment of the present application. The embodiment of the present application is described by taking the example that the USB protocol chip for performing USB protocol interaction may be integrated in the processing module 23.

The FM circuit 22 includes a pass FM filter 221, a blocking FM filter 222, and an FM signal demodulation chip 223, one end of the pass FM filter 221 is connected to the GND pin of the external interface 21, the other end of the pass FM filter 221 is connected to the FM signal demodulation chip 223, and the FM signal demodulation chip 223 is also connected to the processing module 23.

The pass FM filter 221 can propagate FM signals and block non-FM signals, and the block FM filter 222 can filter out FM signals and be used as the main ground. The FM signal demodulation chip 223 is capable of demodulating the received FM signal.

In some embodiments, the pass FM filter 221 may be a bandpass filter whose center frequency may be designed to be the center frequency of the FM band and whose passband bandwidth is designed to cover the FM band to pass FM signals. Then, the impedance of the FM filter 221 to the signal of the FM signal related band is small, while the impedance of the signal of the other band is large. For example, the pass FM filter 221 may be an 80 MHz-100 MHz band pass filter.

The pass FM filter 221 may be designed using resistors, capacitors, inductors, etc. in concert or using application specific integrated circuits. Illustratively, the pass FM filter 221 may be a pi filter or the like.

In some embodiments, the band reject filter 222 may be a band reject filter whose center frequency may be designed to be the center frequency of the FM band and the reject band bandwidth is designed to cover the FM band. Then, the impedance of the FM filter 222 to the signal in the frequency band associated with the FM signal is relatively high, while the impedance of the signal in the other frequency band is relatively low.

The FM-rejection filter 222 may be a magnetic bead, etc., which has a higher resistivity and permeability, and may be equivalent to series connection of a resistor and an inductor, but the resistance and the inductance both change with frequency, and the magnetic bead exhibits resistance at high frequency and can maintain a higher impedance in a wider frequency range, so that FM signals with higher frequency can be effectively filtered by selecting a magnetic bead with a suitable parameter.

In the scenario that the TYPE-C digital earphone is used as the FM antenna, the TYPE-C interface of the TYPE-C digital earphone is inserted into the external interface 21 of the electronic device 20, and the GND pin of the TYPE-C digital earphone is connected to the GND pin of the electronic device 20, that is, the ground wire (the signal wire connected to the GND pin of the TYPE-C digital earphone) of the TYPE-C digital earphone is used as the FM antenna, and the d+ pin and the D-pin of the TYPE-C digital earphone are connected to the d+ pin and the D-pin of the electronic device 20. Specifically, the processing module 23 performs USB protocol interaction (transmitting USB protocol signals, that is, USB data) with the external device through the d+ pin and the D-pin, so as to determine that the external interface 21 is a digital earphone, meanwhile, the FM antenna (the ground wire of the TYPE-C digital earphone) picks up the FM analog signal, the FM analog signal (analog) is propagated to the FM signal demodulation chip 223 by the FM filter 221, and the FM signal demodulation chip 223 demodulates the FM analog signal into FM data (for example, the FM analog signal is converted into the FM digital signal) and then sends the FM digital signal to the processing module 23 for processing, and finally sends the FM digital signal to the user for listening.

It will be appreciated that when the TYPE-C analog earphone is used as the FM antenna, and the TYPE-C interface of the TYPE-C analog earphone is plugged into the external interface 21 of the electronic device 20, the FM function, that is, the local antenna on the SBU pin, may be implemented by connecting other pins (such as SBU pins) of the TYPE-C analog earphone with other pins (such as SBU pins) of the electronic device 20. When the TYPE-C digital earphone is used as the FM antenna, the SBU pin of the external interface 21 of the electronic equipment 20 is suspended.

Through researches, when the ground wire of the TYPE-C digital earphone is used as an FM antenna to realize the FM function, larger noise exists on the ground wire, and the FM function cannot be realized better. Through further analysis and actual measurement, noise on the ground wire of the TYPE-C digital earphone mainly originates from high-frequency components of the USB protocol signal, but because the noise frequency falls in the frequency band of the FM signal, the conventional filter circuit cannot effectively distinguish the FM signal from the noise, for example, the frequency of the USB protocol signal is 1.2 MHz, 12 MHz and the like, the frequency range of the FM signal is 88 MHz to 100 MHz, the high-frequency components of the USB protocol signal are more than 90, so that the frequency of the USB protocol signal is not in the frequency range of 88 MHz to 100 MHz of the FM signal, and the high-frequency components of the USB protocol signal are in the frequency range of 88 MHz to 100 MHz of the FM signal.

Based on the above, the embodiment of the application also provides an FM circuit which can filter out high-frequency noise overlapped with the FM frequency band on the FM antenna of the TYPE-C digital earphone, improve the quality of FM signals and promote the user experience.

Referring to fig. 5, fig. 5 is a circuit diagram of an electronic device according to an embodiment of the present application. As shown in fig. 5, unlike the FM circuit shown in fig. 4, the FM circuit 22 in the electronic device 20 shown in fig. 5 includes not only the pass FM filter 221, the blocking FM filter 222, and the FM signal demodulation chip 223, but also a noise processing unit and two other pass FM filters. Specifically, the FM circuit 22 includes a first connection terminal (also referred to as a ground connection terminal) P1, a second connection terminal P2, a third connection terminal P3 (the second connection terminal P2 and the third connection terminal P3 are collectively referred to as protocol signal connection terminals), a fourth connection terminal (also referred to as output connection terminals) P4, a three-pass FM filter, an anti-FM filter 222, a noise processing unit 226, and an FM signal demodulation chip 223. For distinction, the three-pass FM filters are a first-pass FM filter (i.e., the pass FM filter in fig. 4) 221, a second-pass FM filter 224, and a third-pass FM filter 225, respectively. The noise processing unit 226 includes a first input terminal IN1, a second input terminal IN2, a third input terminal IN3, and an output terminal OUT. The first connection terminal P1 is connected to the GND pin of the external interface 21, one end of the first pass FM filter 221, and one end of the resistance FM filter 222, respectively, and the other end of the first pass FM filter 221 is connected to the first input terminal IN1 of the noise processing unit 226, and the other end of the resistance FM filter 222 is grounded. The second connection end P2 is respectively connected to the D-pin of the external interface 21, one end of the second through FM filter 224, and the processing module 23, the third connection end P3 is respectively connected to the d+ pin of the external interface 21, one end of the third through FM filter 225, and the processing module 23, the other end of the second through FM filter 224 is connected to the second input end IN2 of the noise processing unit 226, the other end of the third through FM filter 225 is connected to the third input end IN3 of the noise processing unit 226, the output end OUT of the noise processing unit 226 is connected to the FM signal demodulation chip 223, the FM signal demodulation chip 223 is also connected to the fourth connection end P4, and the fourth connection end P4 is connected to the processing module 23.

The second pass FM filter 224 and the third pass FM filter 225 described above are each capable of propagating FM signals while blocking non-FM signals. Since the high frequency components of the USB protocol signal (also referred to as interference signals in the FM signal band) fall within the FM signal band, and the USB protocol signal does not fall within the FM signal band, the second pass FM filter 224 and the third pass FM filter 225 are able to propagate the high frequency components of the USB protocol signal (while avoiding the sampling trace branching from degrading the USB signal eye) while preventing the USB protocol signal.

In the scenario that the TYPE-C digital earphone is used as the FM antenna, the TYPE-C interface of the TYPE-C digital earphone is inserted into the external interface 21 of the electronic device 20, and the GND pin of the TYPE-C digital earphone is connected to the GND pin of the electronic device 20, that is, the ground wire (the signal wire connected to the GND pin of the TYPE-C digital earphone) of the TYPE-C digital earphone is used as the FM antenna, and the d+ pin and the D-pin of the TYPE-C digital earphone are connected to the d+ pin and the D-pin of the electronic device 20. Specifically, the processing module 23 performs USB protocol interaction (transmitting a USB protocol signal, i.e. USB data) with the TYPE-C digital earphone through the d+ pin and the D-pin, so as to determine that the external interface 21 is the digital earphone, and at the same time, the FM analog signal picked up by the FM antenna (the ground wire of the TYPE-C digital earphone) is transmitted to the first pass FM filter 221 through the GND pin of the external interface 21. As can be seen from the foregoing, the noise on the ground line of the TYPE-C digital earphone mainly originates from the high frequency component of the USB protocol signal, and the noise frequency falls within the FM signal band, so the signal propagated by the first pass FM filter 221 includes not only the useful FM signal but also the interference signal within the FM band (i.e., the high frequency component of the USB protocol signal), that is, the noise processing unit 226 receives the useful FM analog signal propagated by the first pass FM filter 221 and the interference signal within the FM band through the first input terminal IN 1. While the processing module 23 performs USB protocol interaction with the TYPE-C digital earphone through the d+ pin and the D-pin, the noise processing unit 226 receives, through the second input terminal IN2, an interference signal IN the FM band propagated by the second through FM filter 224, and receives, through the third input terminal IN3, an interference signal IN the FM band propagated by the third through FM filter 225. The noise processing unit 226 processes the FM analog signal received by the first input terminal IN1 and the interference signal IN the FM frequency band, the interference signal received by the second input terminal IN2, and the interference signal IN the FM frequency band received by the third input terminal IN3, for example, subtracting the FM analog signal received by the second input terminal IN1 and the interference signal IN the FM frequency band received by the second input terminal IN2 and the interference signal IN the FM frequency band received by the third input terminal IN3 from each other, so as to obtain an FM analog signal (analog) for filtering the interference signal IN the FM frequency band (i.e., the high frequency component of the USB protocol signal). The FM analog signal (analog) not including the interference signal propagates to the FM signal demodulation chip 223, and the FM signal demodulation chip 223 demodulates the FM analog signal into FM data, and then sends the FM data to the processing module 23 for processing, and finally sends the FM data to the user for listening.

In summary, in the FM circuit provided by the embodiment of the application, the USB protocol signals on the d+ pin and the D-pin of the TYPE-C digital earphone are bandpass filtered by the second passband FM filter 224 and the third passband FM filter 225, and the high frequency noise in the FM signal band is sampled and then input to the noise processing unit 226; the ground wire of the TYPE-C digital earphone is connected to the first pass FM filter 221 and the anti-FM filter 222 through the GND pin of the electronic device 20, the signal on the ground wire of the TYPE-C digital earphone is divided into two paths, one path is used as the main ground after filtering the FM signal by the anti-FM filter 222, and the other path is used to retain the FM signal (including the useful FM signal and the interference signal in the FM frequency band) after using the first pass FM filter 221 and inputs the FM signal into the noise processing unit 226. In the noise processing unit 226, the FM signal subtracts the high frequency noise transmitted on the d+ pin and the D-pin to obtain an FM antenna signal with the USB harmonic component filtered, and the FM signal is passed through the FM signal demodulation chip 223 to implement the FM function. The FM circuit provided by the embodiment of the application filters out high-frequency noise overlapped with the FM frequency band on the FM antenna of the TYPE-C digital earphone, avoids the problem that the FM function cannot be better realized due to larger noise on the ground wire when the ground wire of the TYPE-C digital earphone is used as the FM antenna to realize the FM function, improves the quality of FM signals and improves the user experience.

In some embodiments, the second pass FM filter 224 and the third pass FM filter 225 may be bandpass filters whose center frequencies may be designed to be the center frequencies of the FM frequency band, and whose passband bandwidths are designed to cover the FM frequency band to pass high frequency components of the USB protocol signals that fall within the FM signal frequency band. Then, the second through FM filter 224 and the third through FM filter 225 have small impedance for the high frequency components of the USB protocol signal that fall within the FM signal band, while the impedance for the signals of the other bands is large. For example, the second pass FM filter 224 and the third pass FM filter 225 may be 80mhz to 100mhz band pass filters.

The second pass FM filter 224 and the third pass FM filter 225 may be co-designed using resistors, capacitors, inductors, etc. or using application specific integrated circuits. Illustratively, the second pass FM filter 224 and/or the third pass FM filter 225 may be pi filters or the like.

Here, the structures of the first pass FM filter 221, the second pass FM filter 224, and the third pass FM filter 225 may be identical; may also be different; it is also possible that the two pass FM filters have the same structure, e.g., the second pass FM filter 224 and the third pass FM filter 225 have the same structure, and the first pass FM filter 221 has a different structure from the second pass FM filter 224 and the third pass FM filter 225. Embodiments of the present application are not limited in this regard as long as it is capable of propagating FM signals while blocking non-FM signals.

For a specific structure of the noise processing unit 226, in some embodiments, referring to fig. 6, fig. 6 is a circuit diagram of a noise processing unit according to an embodiment of the present application. As shown IN fig. 6, the noise processing unit 226 includes, IN addition to the first input terminal IN1, the second input terminal IN2, the third input terminal IN3, and the output terminal OUT described above, a first input resistor unit R1, a second input resistor unit R2, a third input resistor unit R3, a fourth input resistor unit R4, a feedback resistor unit Rf, and an operational amplifier a, one end of the first input resistor unit R1 is connected to the third input terminal IN3, one end of the second input resistor unit R2 is connected to the second input terminal IN2, one end of the third input resistor unit R3 is connected to the first input terminal IN1, the other end of the first input resistor unit R1 is connected to one end of the feedback resistor unit Rf, the other end of the second input resistor unit R2, and an inverting terminal of the operational amplifier a, the other end of the feedback resistor unit Rf is connected to the output terminal OUT of the noise processing unit 226 and the output terminal of the operational amplifier a, respectively, the other end of the third input resistor unit R3 is connected to one end of the fourth input resistor unit R4 and the other end of the operational amplifier a, and the other end of the input resistor unit R4 is grounded.

The noise processing unit 226 receives the voltage of the interference signal IN the FM band propagated by the second FM filter 224 through the second input terminal IN2, the voltage of the interference signal IN the FM band propagated by the third FM filter 225 through the third input terminal IN3, the voltage of the FM analog signal propagated by the first FM filter 221 and the voltage of the interference signal IN the FM band received by the first input terminal IN1, vin2, and Vout at the output terminal OUT of the noise processing unit 226.

By utilizing the characteristics of the operational amplifier, such as the virtual short (the voltages of the same phase end and the opposite phase end) and the virtual break (the current flowing into and out of the input pin of the operational amplifier is 0), and the kirchhoff law, and the related knowledge of the circuit superposition theorem and the subtracting operation circuit, the following can be obtained: vout=Rf (Vin 1/R1-Vin3/R3-Vin 2/R2).

That is, after the processing of the operational amplifier a, the filtered FM antenna signal Vout is obtained, where the FM antenna signal Vout is an FM analog signal, an FM analog signal (analog) that does not include an interference signal in the FM band propagates to the FM signal demodulation chip 223, and the FM signal demodulation chip 223 demodulates the FM analog signal into FM data (e.g., converts the FM analog signal into an FM digital signal), and then sends the FM digital signal to the processing module 23 for processing, and finally sends the FM digital signal to the user for listening.

For the resistances of the first, second, third, and fourth input resistance units R1, R2, R3, R4, in some embodiments, the resistances of the first, second, third, and fourth input resistance units R1, R2, R3, R4 satisfy: rf > > R1// R2 (i.e. the resistance of the feedback resistance unit Rf is much greater than the resistance of the first input resistance unit R1 and the second input resistance unit R2 after being connected in parallel); r1> > R4 (i.e. the resistance of the first input resistor unit R1 is much larger than the resistance of the fourth input resistor unit R4).

The above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the application.

Claims

1. A frequency modulated broadcast circuit, comprising: the system comprises a ground wire connection end, a protocol signal connection end, an output connection end, a first pass FM filter unit, a second pass FM filter unit, a resistance FM filter unit, a noise processing unit and an FM signal demodulation chip;

The ground wire connecting end is respectively connected with one end of the first pass FM filter unit and one end of the resistance FM filter unit, the protocol signal connecting end is connected with one end of the second pass FM filter unit, the other end of the first pass FM filter unit and the other end of the second pass FM filter unit are respectively connected with the input end of the noise processing unit, the other end of the resistance FM filter unit is grounded, and the FM signal demodulation chip is respectively connected with the output end and the output connecting end of the noise processing unit;

The second through FM filter unit is used for transmitting interference signals in an FM frequency band generated when the protocol signal connection end transmits the protocol signals to the noise processing unit;

The first pass FM filter unit is used for transmitting an FM signal picked up by the ground wire of the TYPE-C digital earphone received by the ground wire connection end to the noise processing unit, wherein the FM signal transmitted by the first pass FM filter unit comprises a useful FM signal and an interference signal in an FM frequency band;

the noise processing unit is used for processing the FM signal and the interference signal in the FM frequency band to obtain the useful FM signal;

the FM signal demodulation chip is used for demodulating the useful FM signal into FM data and outputting the FM data through the output connection end.

2. The fm broadcast circuit of claim 1, wherein the protocol signal connection comprises a first protocol signal connection and a second protocol signal connection;

The first pass FM filter unit comprises a first pass FM filter, and the second pass FM filter unit comprises a second pass FM filter and a third pass FM filter;

The ground wire connecting end is connected with one end of the first pass FM filter, the first protocol signal connecting end is connected with one end of the second pass FM filter, the second protocol signal connecting end is connected with one end of the third pass FM filter, and the other end of the first pass FM filter, the other end of the second pass FM filter and the other end of the third pass FM filter are respectively connected with the input end of the noise processing unit;

the second through FM filter is used for transmitting interference signals in an FM frequency band generated when the first protocol signal connection end receives a protocol signal to the noise processing unit;

The third three-way FM filter is used for transmitting interference signals in an FM frequency band generated when the second protocol signal connection end receives a protocol signal to the noise processing unit;

The first pass FM filter unit is used for transmitting the FM signal picked up by the ground wire of the TYPE-C digital earphone received by the ground wire connection end to the noise processing unit, wherein the FM signal transmitted by the first pass FM filter unit comprises a useful FM signal and an interference signal in an FM frequency band.

3. The FM broadcast circuit of claim 2, wherein the first pass FM filter, the second pass FM filter, and the third pass FM filter are identical in structure.

4. The fm broadcast circuit according to claim 2, wherein the noise processing unit includes a first input terminal, a second input terminal, a third input terminal, an output terminal, a first input resistor unit, a second input resistor unit, a third input resistor unit, a fourth input resistor unit, a feedback resistor unit, and an operational amplifier, one end of the first input resistor unit is connected to the third input terminal, one end of the second input resistor unit is connected to the second input terminal, one end of the third input resistor unit is connected to the first input terminal, the other end of the first input resistor unit is connected to one end of the feedback resistor unit, the other end of the second input resistor unit, and an inverting terminal of the operational amplifier, the other end of the feedback resistor unit is connected to an output terminal of the noise processing unit and an output terminal of the operational amplifier, respectively, the other end of the third input resistor unit is connected to one end of the fourth input resistor unit and an input terminal of the operational amplifier, and the other end of the fourth input resistor unit is grounded.

5. The fm broadcast circuit of claim 4, wherein the feedback resistor unit has a resistance substantially greater than a resistance of the first input resistor unit and the second input resistor unit in parallel; and/or the resistance value of the first input resistance unit is far greater than the resistance value of the fourth input resistance unit.

6. A fm broadcast circuit as claimed in claim 4, wherein the voltage Vout at the output of the noise handling unit satisfies: vout=rf (Vin 1/R1-Vin3/R3-Vin 2/R2);

Wherein Vin3 is the voltage of the interference signal in the FM frequency band propagated by the third pass FM filter, vin2 is the voltage of the interference signal in the FM frequency band propagated by the second pass FM filter, vin1 is the voltage of the useful FM signal propagated by the first pass FM filter and the interference signal in the FM frequency band, rf is the resistance of the feedback resistor unit, R1 is the resistance of the first input resistor unit, R2 is the resistance of the second input resistor unit, and R3 is the resistance of the third input resistor unit.

7. The frequency modulated broadcast circuit of claim 2, wherein the first pass FM filter, the second pass FM filter, and/or the third pass FM filter comprise band pass filters.

8. An electronic device comprising an external interface, a processing module and the fm broadcast circuit of any of claims 1-7;

the external interface comprises a grounding pin and a protocol pin;

The ground wire connecting end of the frequency modulation broadcasting circuit is connected with the grounding pin of the external interface, the protocol signal connecting end of the frequency modulation broadcasting circuit is respectively connected with the protocol pin of the external interface and the processing module, and the output connecting end of the frequency modulation broadcasting circuit is connected with the processing module;

When the TYPE-C digital earphone is inserted into the external interface, the processing module is used for transmitting protocol signals with the TYPE-C digital earphone through the protocol signal connecting end of the frequency modulation broadcasting circuit and the protocol pin of the external interface so as to perform protocol interaction; and the receiving antenna is also used for processing the FM data output by the output connection end so as to enable the TYPE-C digital earphone to be used as a receiving antenna of an FM signal to realize an FM function.

9. The electronic device of claim 8, wherein the external interface comprises a USB Type-C interface.

10. The electronic device of claim 9, wherein the protocol signal connection comprises a first protocol signal connection and a second protocol signal connection; the first protocol signal connection end is a D-pin of the USB Type-C interface, and the second protocol signal connection end is a D+ pin of the USB Type-C interface.