CN114244353B - Quick start crystal oscillator based on secondary injection and phase-locked loop technology - Google Patents

Quick start crystal oscillator based on secondary injection and phase-locked loop technology Download PDF

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Publication number
CN114244353B
CN114244353B CN202111570166.3A CN202111570166A CN114244353B CN 114244353 B CN114244353 B CN 114244353B CN 202111570166 A CN202111570166 A CN 202111570166A CN 114244353 B CN114244353 B CN 114244353B
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phase
crystal oscillator
frequency
locked loop
voltage
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CN114244353A (en
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周波
李一凡
韩欣媛
郑恒
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Beijing Institute of Technology BIT
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
    • H03L7/089—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal the phase or frequency detector generating up-down pulses
    • H03L7/0891—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal the phase or frequency detector generating up-down pulses the up-down pulses controlling source and sink current generators, e.g. a charge pump
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/099—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop
    • H03L7/0995—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop the oscillator comprising a ring oscillator
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention relates to a quick start crystal oscillator based on a secondary injection and phase-locked loop technology, and belongs to the technical field of clock generation. The device comprises a quartz crystal oscillator, a phase frequency detector, a charge pump, a low-pass filter, a ring voltage-controlled oscillator, a tri-state gate and a digital control module; the quartz crystal oscillator adopts a Pierce structure; the phase frequency detector and the charge pump are of a fully differential structure; the low-pass filter adopts a third-order fully-differential passive RC structure; the voltage-controlled oscillator adopts a three-stage inverter chain cascade charge-discharge structure. The quartz crystal oscillator is connected with the phase frequency detector, the phase frequency detector is connected with the charge pump, the charge pump is connected with the low-pass filter, the low-pass filter is connected with the voltage-controlled oscillator, the voltage-controlled oscillator is connected with the phase frequency detector and the tri-state gate, and the tri-state gate is connected with two ends of the crystal resonator of the crystal oscillator. The phase-locked loop in the framework can enable the voltage-controlled oscillator to rapidly and accurately lock the frequency to the reference frequency, and the secondary injection technology enables the crystal oscillator to output stable reference frequency in a very short time, so that the starting time of the crystal oscillator is shortened from ms level to mu s level; the phase-locked loop works in an intermittent mode with low duty ratio, and the introduced power consumption is negligible; the differential frequency correction loop can reduce the size of a filter capacitor and the conversion gain of the VCO, optimize the hardware cost of a circuit, and improve the noise suppression and anti-interference capability of the crystal oscillator.

Description

Quick start crystal oscillator based on secondary injection and phase-locked loop technology
Technical Field
The invention relates to a quick start crystal oscillator based on a secondary injection and phase-locked loop technology, and belongs to the technical field of clock generation.
Background
The oscillator is used as an energy conversion device, and can convert direct-current electric energy into alternating-current electric energy with specific frequency through positive feedback under the condition of no input signal control, so as to provide clock signals for other circuits.
The quartz crystal has its natural frequency, when the alternating voltage frequency applied to the two ends of the quartz crystal is equal to the natural frequency, resonance phenomenon is generated, the internal current of the crystal oscillator is greatly enhanced, and the quartz crystal oscillator is an electronic device manufactured by utilizing the principle. The frequency stability of a quartz crystal oscillator can be easily orders of magnitude lower than 10 -8. Because of its high frequency stability, quartz crystal oscillators are widely used in electronic instruments requiring timing, such as satellite navigation, broadcast television, mobile communication, radar, etc.
The high frequency stability of a crystal oscillator results from the high quality factor of the quartz crystal, but the high quality factor results in a strict energy screening, which results in a slow onset of oscillation, typically on the order of milliseconds. Crystal oscillators are used to provide the accurate clock required for high frequency synthesis in all wireless systems, which are turned on for a short period of time and off in most cases, in order to reduce average power consumption, and which often require frequent start-up of the crystal oscillator; in this case, although a high quality factor of the quartz crystal is advantageous for obtaining excellent frequency stability, it also results in a higher energy loss during the start-up of the crystal oscillator.
In order to reduce the start-up time, an energy injection method for increasing the initial noise energy in the crystal resonator at the start-up is generally used, the oscillator principle is to select a noise signal with a resonance frequency from the initial noise and amplify the initial energy in the crystal by the energy injection method, so that the crystal starts to vibrate rapidly.
Disclosure of Invention
The invention provides a quick start crystal oscillator based on a secondary injection and phase-locked loop technology, and aims to improve the starting speed of the existing crystal oscillator. An automatic frequency calibration technology is adopted to realize the accuracy of the frequency of the injection signal during the second energy injection; meanwhile, in the automatic frequency calibration process, a phase-locked loop (PLL) technology is adopted, so that the accuracy of the frequency of the injection signal is ensured.
The invention is realized by the following technical scheme:
The fast start crystal oscillator based on the secondary injection and phase-locked loop technology comprises a crystal oscillator XTO, a phase-locked loop PLL (phase frequency detector PFD, a charge pump CP, a low pass filter LPF, a Ring voltage controlled oscillator Ring VCO), a tri-state gate TSG and a digital control module;
The crystal oscillator XTO is a three-point amplifier with a Pears structure and is realized by a low-voltage CMOS (complementary metal oxide semiconductor) to reduce the overall power consumption of the system;
The phase-locked loop circuit PLL comprises a Ring voltage-controlled oscillator Ring VCO, a phase frequency detector PFD, a charge pump CP and a low pass filter LPF;
The PFD is of a fully differential structure, called fully differential phase frequency detector, and is realized through a static CMOS logic gate circuit, so that the overall power consumption of the system is reduced;
The charge pump CP is implemented by adopting a fully differential CMOS push-pull structure, and is called a fully differential charge pump;
the low-pass filter LPF adopts a third-order fully-differential passive RC structure;
The Ring voltage-controlled oscillator Ring VCO is a three-stage pull-in current charge-discharge type Ring voltage-controlled oscillator and is composed of a voltage-current converter (V-to-I) and a three-stage cascading digital inverter chain;
The tri-state gate TSG is implemented by a static CMOS digital logic circuit.
The connection relation of each module in the quick start crystal oscillator based on the secondary injection and phase-locked loop technology is as follows:
The crystal oscillator XTO is connected with the reference frequency input end of the phase-locked loop PLL, the output end of the phase-locked loop PLL is connected with the tri-state gate TSG, the tri-state gate TSG is connected with the two ends X1 and X2 of the crystal resonator XTAL in the crystal oscillator XTO, and the digital control module is connected with the tri-state gate TSG and the phase-locked loop PLL.
The Ring-shaped voltage-controlled oscillator Ring VCO in the phase-locked loop PLL is connected with the phase frequency detector PFD, the phase frequency detector PFD is connected with the charge pump CP, the charge pump CP is connected with the low-pass filter LPF, the low-pass filter LPF is connected with the Ring-shaped voltage-controlled oscillator Ring VCO, and the digital control module is connected with the phase frequency detector PFD, the charge pump CP, the low-pass filter LPF and the Ring-shaped voltage-controlled oscillator Ring VCO.
The design process of the fast start crystal oscillator based on the secondary injection and phase-locked loop technology comprises the steps that the Ring voltage-controlled oscillator Ring VCO injects energy into the crystal resonator XTAL for the first time, the phase-locked loop PLL frequency is tracked, and the Ring voltage-controlled oscillator Ring VCO injects energy into the crystal resonator XTAL for the second time;
The method specifically comprises the following steps:
step one, the Ring VCO injects energy into the XTAL for the first time, and specifically includes the following sub-steps:
Step 1.1, under the action of a START signal START and a reset signal NRST, resetting each output signal of the digital control module, wherein the input ends V CP and V CN of the Ring voltage-controlled oscillator Ring VCO are both connected with a common mode voltage V CM, the Ring voltage-controlled oscillator Ring VCO STARTs working under the control of the digital control module, and outputs a signal S 1 with the frequency close to the natural frequency of the crystal resonator;
At this time, the tri-state gate TSG is in a conducting state under the control of the digital control module, and the signal S 1 is transmitted to the two ends X1 and X2 of the crystal resonator XTAL through the tri-state gate;
Step 1.2, the crystal oscillator XTO outputs a signal S 2 with the same frequency as S 1 under the action of the signal S 1, and uses the signal S 2 as a clock signal of the digital control module;
After the first energy injection is completed, the tri-state gate TSG is switched into a high-resistance state under the time logic control of the digital control module, the Ring voltage-controlled oscillator Ring VCO is disconnected with the crystal oscillator XTO, the crystal oscillator XTO outputs a signal X 2 with smaller amplitude, higher phase noise and more stable frequency, and a clock signal S 2 with full amplitude, higher phase noise and stable frequency is obtained after the signal X 2 passes through the intermediate frequency amplifier;
step two, phase-locked loop PLL frequency tracking, specifically comprising the following sub-steps:
Step 2.1, the crystal oscillator XTO outputs a signal X 2 with smaller amplitude, relatively higher phase noise and more stable frequency after the energy is injected for the first time, the signal is amplified by an intermediate frequency amplifier to generate a square wave signal S 2, and the signal S 2 is input into a phase-locked loop PLL to be used as the reference frequency of a phase frequency detector PFD;
At this time, the phase-locked loop PLL enters a working state under the control of the digital control module, the control voltage V CP、VCN of the Ring voltage controlled oscillator Ring VCO is connected to the low pass filter LPF, and the Ring voltage controlled oscillator Ring VCO outputs an initialization signal S 1;
Step 2.2, the PFD compares the Ring VCO signal S 1 with the reference signal S 2 and outputs the phase difference pulse signals UPN, UPP, DNP and DNN in full differential form;
Pulse signals UPN, UPP, DNP and DNN control a charge pump CP to output fully differential pulse currents CON and COP to a low-pass filter LPF, under the regulation of the pulse currents, the output voltage V CP、VCN of the low-pass filter LPF is continuously changed, and the voltage V CP、VCN controls the output frequency of a Ring voltage-controlled oscillator Ring VCO to be continuously changed;
step 2.3, under the action of automatic frequency calibration of a phase-locked loop (PLL), the output frequency of a Ring VCO is gradually locked to the expected output frequency (12 MHz);
After the frequency locking is completed, under the control of the digital control module, the switches D1 and D2 are disconnected, and the voltage V CP、VCN stored on the large capacitor has no charge leakage channel, so that the voltage is kept unchanged in a short time (longer than the second energy injection time), and the frequency of the Ring VCO output signal S 1 is locked;
Step three, the Ring VCO injects energy into the XTAL for the second time, specifically including the following sub-steps:
Step 3.1, the tri-state gate TSG is in a conducting state under the control of the digital control module, and the Ring VCO output signal S 1 is transmitted to the two ends X1 and X2 of the XTAL through the tri-state gate, so as to inject energy into the XTAL;
And 3.2, controlling the second energy injection time through a digital control module, switching the tri-state gate TSG to a high-resistance state after the second energy injection is completed, ending the working state of the phase-locked loop PLL, stopping the work of the phase frequency detector PFD, the charge pump CP and the Ring voltage controlled oscillator Ring VCO, resetting the output to a low potential, completing the quick start of the crystal oscillator XTO, and outputting a signal S 2 with high stability and low phase noise.
Advantageous effects
Compared with the existing crystal oscillator design method, the quick start crystal oscillator based on the secondary injection and phase-locked loop technology has the following beneficial effects:
1. the crystal oscillator XTO adopts a Pierce structure three-point amplifier, and is realized by a low-voltage CMOS, so that the overall power consumption of the system is reduced;
2. The secondary injection technology adopts an automatic frequency calibration technology, so that the signal frequency can be obviously close to the XTAL resonance frequency of the quartz crystal resonator, and the injection energy and the injection efficiency are effectively improved;
3. The automatic frequency calibration technology adopts a phase-locked loop (PLL) technology, works in a gap type working mode with extremely low duty ratio, and can reduce the chip cost and obviously reduce the power consumption of a frequency calibration system on the premise of meeting the frequency error requirement;
4. compared with the primary energy injection technology, the crystal oscillator adopting the secondary injection technology and the phase-locked loop technology can obviously increase the initial energy in the crystal resonator and effectively reduce the starting time of the quartz crystal oscillator; optimizing the start-up time from ms level to μs level;
5. the differential PFD, CP and LPF structure not only reduces the size of the filter capacitor by more than 50%, but also reduces the conversion gain of the VCO by half, optimizes the hardware cost and noise performance of the circuit, suppresses the common mode noise of the phase-locked loop, and improves the anti-interference capability of the crystal oscillator.
Drawings
FIG. 1 is a system block diagram of a fast start crystal oscillator based on a two-shot and phase-locked loop technique of the present invention;
FIG. 2 is a schematic diagram of the XTO circuit of the crystal oscillator in the fast start crystal oscillator based on the two-shot and phase-locked loop technique according to the invention;
fig. 3 is a circuit diagram of a PFD circuit in a fast start crystal oscillator based on a two-shot and phase-locked loop technique according to the present invention;
FIG. 4 is a block diagram of a charge pump CP circuit in a fast start crystal oscillator based on a two-shot and phase locked loop technique of the present invention;
FIG. 5 is a block diagram of the LPF circuit of a fast start crystal oscillator based on the two-shot and phase-locked loop technique of the present invention;
FIG. 6 is a circuit diagram of a voltage-to-current converter (V-to-I) in a fast start crystal oscillator based on a two-shot and phase locked loop technique according to the present invention;
FIG. 7 is a circuit block diagram of a three-stage ring oscillator in a fast start crystal oscillator based on a two-shot and phase locked loop technique in accordance with the present invention;
FIG. 8 is a schematic diagram of a three-state gate TSG circuit in a fast start crystal oscillator based on a two-shot and phase-locked loop technique in accordance with the present invention;
FIG. 9 is a schematic diagram of the current of an equivalent dynamic branch circuit when the crystal injection energy in a crystal oscillator is rapidly started based on the two-shot and phase-locked loop technique according to the present invention;
FIG. 10 is a timing diagram of the PLL output frequency lock in a fast start crystal oscillator based on the two-shot and PLL technique of the present invention;
fig. 11 is a timing diagram of the XTO output signal of a fast start crystal oscillator based on the two-shot and phase-locked loop technique according to the present invention;
fig. 12 is a signal timing diagram of two ends X1 and X2 of the crystal resonator XTAL without a fast start module in a fast start crystal oscillator based on the two-shot and phase-locked loop technique according to the present invention;
fig. 13 is a phase noise diagram of the XTO output signal of the crystal oscillator in the fast start crystal oscillator based on the two-shot and phase locked loop technique according to the present invention;
Detailed Description
The following describes the circuit modules and the working process of the fast start crystal oscillator based on the secondary injection and phase-locked loop technology in detail by referring to the embodiments and the drawings.
Example 1
A fast start crystal oscillator based on the secondary injection and phase-locked loop technology can be applied to a circuit which needs to rapidly provide a reference clock, and the overall power consumption of the circuit is reduced.
The block diagram of the invention is shown in fig. 1, and the fast start crystal oscillator based on the secondary injection and phase-locked loop technology mainly comprises a crystal oscillator XTO, a phase-locked loop PLL (phase frequency detector PFD, a charge pump CP, a low pass filter LPF, a Ring voltage controlled oscillator Ring VCO), a tri-state gate TSG and a digital control module.
The crystal oscillator XTO is a three-point amplifier with a Pears structure and is realized by a low-voltage CMOS (complementary metal oxide semiconductor) to reduce the overall power consumption of the system;
The phase-locked loop circuit PLL comprises a Ring voltage-controlled oscillator Ring VCO, a phase frequency detector PFD, a charge pump CP and a low pass filter LPF;
The PFD is of a fully differential structure, called fully differential phase frequency detector, and is realized through a static CMOS logic gate circuit, so that the overall power consumption of the system is reduced;
The charge pump CP is implemented by adopting a fully differential CMOS push-pull structure, and is called a fully differential charge pump;
the low-pass filter LPF adopts a third-order fully-differential passive RC structure;
The Ring voltage-controlled oscillator Ring VCO is a three-stage pull-in current charge-discharge type Ring voltage-controlled oscillator and is composed of a voltage-current converter (V-to-I) and a three-stage cascading digital inverter chain;
The tri-state gate TSG is implemented by a static CMOS digital logic circuit.
The connection relation of each module in the quick start crystal oscillator based on the secondary injection and phase-locked loop technology is as follows:
The crystal oscillator XTO is connected with the reference frequency input end of the phase-locked loop PLL, the output end of the phase-locked loop PLL is connected with the tri-state gate TSG, the tri-state gate TSG is connected with the two ends X1 and X2 of the crystal resonator XTAL in the crystal oscillator XTO, and the digital control module is connected with the tri-state gate TSG and the phase-locked loop PLL. The Ring-shaped voltage-controlled oscillator Ring VCO in the phase-locked loop PLL is connected with the phase frequency detector PFD, the phase frequency detector PFD is connected with the charge pump CP, the charge pump CP is connected with the low-pass filter LPF, the low-pass filter LPF is connected with the Ring-shaped voltage-controlled oscillator Ring VCO, and the digital control module is connected with the phase frequency detector PFD, the charge pump CP, the low-pass filter LPF and the Ring-shaped voltage-controlled oscillator Ring VCO.
The design process based on the secondary injection technology and the phase-locked loop relies on comprises the steps of injecting energy into the crystal resonator XTAL for the first time by the Ring VCO, tracking the frequency of the phase-locked loop PLL, and injecting energy into the crystal resonator XTAL for the second time by the Ring VCO;
The method specifically comprises the following steps:
Step A, the Ring VCO injects energy into the XTAL for the first time, and the method specifically comprises the following sub-steps:
Under the action of a START signal START and a reset signal NRST, the digital control module resets each output signal, the input ends V CP and V CN of the Ring voltage-controlled oscillator Ring VCO are both connected with a common mode voltage V CM, the Ring voltage-controlled oscillator Ring VCO STARTs working under the control of the digital control module, and the output frequency of the Ring voltage-controlled oscillator VCO is close to a signal S 1 of the natural frequency of the crystal resonator;
In particular, in this embodiment, the signal S 1 has a frequency of 11.8859MHz and an error of less than 10% from the 12MHz resonance frequency of the crystal resonator;
At this time, the tri-state gate TSG is in a conducting state under the control of the digital control module, and the signal S 1 is transmitted to the two ends X1 and X2 of the crystal resonator XTAL through the tri-state gate;
Step a.2, the crystal oscillator XTO outputs a signal S 2 with the same frequency as S 1 under the action of the signal S 1, and uses the signal S 2 as a clock signal of the digital control module;
After the first energy injection is completed, the tri-state gate TSG is switched into a high-resistance state under the time logic control of the digital control module, the Ring voltage-controlled oscillator Ring VCO is disconnected with the crystal oscillator XTO, the crystal oscillator XTO outputs a signal X 2 with smaller amplitude, higher phase noise and more stable frequency, and a clock signal S 2 with full amplitude, higher phase noise and stable frequency is obtained after the signal X 2 passes through the intermediate frequency amplifier;
In particular to the present embodiment, the frequency of the signal S 2 is 12.0012MHz;
Step B, phase-locked loop PLL frequency tracking, specifically comprising the following sub-steps:
Step B.1, the crystal oscillator XTO outputs a signal X 2 with smaller amplitude, relatively higher phase noise and more stable frequency after the energy is injected for the first time, the signal is amplified by an intermediate frequency amplifier to generate a square wave signal S 2, and the signal S 2 is input into a phase-locked loop PLL to be used as the reference frequency of a phase frequency detector PFD;
At this time, the phase-locked loop PLL enters a working state under the control of the digital control module, the control voltage V CP、VCN of the Ring voltage controlled oscillator Ring VCO is connected to the low pass filter LPF, and the Ring voltage controlled oscillator Ring VCO outputs an initialization signal S 1;
Specifically, in this embodiment, the center frequency of the signal S 1 is 12MHz, the frequency range is 10MHz to 14MHz, and the frequency of the signal S 2 is 12.0012MHz;
Step B.2, the phase frequency detector PFD compares the Ring VCO signal S 1 with the reference signal S 2 and outputs the phase difference pulse signals UPN, UPP, DNP and DNN which are in full differential form and are complementary;
Pulse signals UPN, UPP, DNP and DNN control a charge pump CP to output fully differential pulse currents CON and COP to a low-pass filter LPF, under the regulation of the pulse currents, the output voltage V CP、VCN of the low-pass filter LPF is continuously changed, and the voltage V CP、VCN controls the output frequency of a Ring voltage-controlled oscillator Ring VCO to be continuously changed;
Step B.3, under the action of automatic frequency calibration of a phase-locked loop (PLL), the output frequency of a Ring VCO is gradually locked to the expected output frequency (12 MHz);
After the frequency locking is completed, under the control of the digital control module, the switches D1 and D2 are disconnected, and the voltage V CP、VCN stored on the large capacitor has no charge leakage channel, so that the voltage is kept unchanged in a short time (longer than the second energy injection time), and the frequency of the Ring VCO output signal S 1 is locked;
in particular to the present embodiment, the frequency of the signal S 1 is 12.0062MHz;
step C, the Ring VCO injects energy into the XTAL for the second time, which comprises the following steps:
step C.1, the tri-state gate TSG is in a conducting state under the control of the digital control module, the Ring voltage-controlled oscillator Ring VCO output signal S 1 is transmitted to the two ends X1 and X2 of the crystal resonator XTAL through the tri-state gate, and energy is injected into the crystal resonator XTAL;
In particular, in this embodiment, the frequency of the signal S 1 is 12.0062MHz, and the error from the standard frequency 12MHz is less than 0.05%;
And C.2, controlling the time of the second energy injection through a digital control module, switching the tri-state gate TSG to a high-resistance state after the second energy injection is completed, ending the working state of the phase-locked loop PLL, stopping the work of the phase frequency detector PFD, the charge pump CP and the Ring voltage-controlled oscillator Ring VCO, resetting the output to a low potential, completing the quick start of the crystal oscillator XTO, and outputting a signal S 2 with high stability and low phase noise.
In particular, in this embodiment, the frequency of the output signal S 2 is 12.0005MHz, which is less than 0.05% in frequency error compared to the resonant frequency 12MHz of the crystal resonator XTAL, and the phase noise is about-125 dBc/Hz at a frequency offset of 1 kHz.
Example 2
As shown in fig. 2, the crystal oscillator XTO has a pierce three-point structure and is composed of a MOS transistor, a resistor, and a capacitor. Wherein I B is standard reference current, M 9、M8、M10 forms a simple MOS current mirror, M 2、M3、M4、M5 forms a low-voltage common-source common-gate current mirror, current is provided for a core amplifying tube M 1, and M 6、M7 provides bias voltage for a common-gate end of the low-voltage common-source common-gate current mirror; cc. Rc and M 12、M11 together form an intermediate frequency amplifier, cc filters the direct current value of the voltage of the drain terminal of M 1, and Rc and M 12、M11 determine direct current bias again for the output voltage; the crystal model XTAL, the capacitor C 1、C2 and the resistor Rosc are arranged outside the chip, the pin X 1、X2 is connected into the chip, the capacitor C 1、C2 and the quartz crystal XTAL form a frequency selection network together, and the feedback resistor Rosc enables the direct current voltages of the gate end and the drain end of the crystal oscillator core tube M 1 to be the same, so that a direct current working point is formed.
The phase frequency detector PFD structure is shown in fig. 3. The combined logic circuit formed by the NAND gate compares the phases between the reference signal S 2 and the feedback signal S 1 in real time, realizes the charge and discharge functions of the later stage charge pump, and converts the phase difference between S 2 and S 1 into a charge and discharge current in a narrow pulse form; meanwhile, in order to eliminate dead zone characteristics of the charge pump and dynamic current mismatch errors of the charge pump, a delay unit module and a delay matching module are introduced, so that static and dynamic charge-discharge matching characteristics of the charge pump are ensured.
The circuit implementation of the fully differential charge pump CP is shown in fig. 4. When the reference frequency phase is advanced from the feedback frequency phase, the upn=dnp=0 and upp=dnn=1 of the phase frequency detector output. The charge pump charges the low-pass filter at the rear stage with narrow pulse, and the output voltage is continuously enhanced. Otherwise, discharge is performed to weaken the output voltage. That is, the charge pump and its LPF convert the phase difference information input by the PFD into a smoothed voltage control value. Compared with a single-end structure, the fully differential charge pump is insensitive to current mismatch, has larger output swing amplitude, and can realize better in-band spurious suppression effect.
The third order low pass filter LPF is shown in fig. 5. In the pll circuit, the digital circuit and the charge pump circuit generate switching noise close to the frequency of the reference signal S 2, so in practical application, an additional third-order filter is required to be added on the basis of the second-order passive low-pass filter to attenuate unwanted spurious noise. Compared with a single-ended structure, the differential structure has the advantages that the capacitance value in the differential structure is only one half of that of the single-ended structure, the hardware area can be effectively reduced, meanwhile, the differential structure can effectively inhibit common mode noise, and the conversion gain of the back-stage VCO is reduced.
The voltage-to-current converter circuit in the Ring voltage controlled oscillator Ring VCO is shown in fig. 6. When the voltage V CN is unequal to the voltage V CP, the potentials at the two ends of the resistor R are unequal to generate current, so that the output current of the current mirror is changed, the change amount of the output current is in direct proportion to the voltage difference between the V CP and the V CN, and the linear conversion from the input voltage difference to the output current value is realized.
As shown in FIG. 7, the three-stage ring oscillator in the ring voltage-controlled oscillator is characterized in that I B is a reference current, M 7、M9、M11、M13、M15 tubes form a group of NMOS pull-down current mirrors, M 8、M10、M12、M14 tubes form a group of complementary PMOS up-current mirrors, W/L of corresponding NMOS tubes are identical, and W/L of corresponding PMOS tubes are identical, so that the matching performance is improved; the NMOS tube and the PMOS tube in the three-stage inverter have the same L and the W ratio of about 2/3, so as to improve the symmetry of level conversion. If the equivalent parasitic capacitance of each inverter is C L, the power supply voltage is V DD, and the current source is I B, the output frequency of the three-stage ring oscillator is:
fosc＝IB/(3CLVDD)
The output frequency f osc is proportional to the current I B and I B is proportional to the input voltage difference, thereby achieving a linear conversion of the input voltage to the output frequency. In the second injection, the switch D 1、D2 is turned off, the output voltage V CP、VCN of the low-pass filter is fixed, and the error between the frequency of the output signal S 1 of the voltage-controlled oscillator and the resonance frequency 12MHz of the quartz crystal is 0.0062MHz at maximum, and the error is about equal to 0.05%.
As shown in fig. 8, the tri-state gate TSG is formed of a CMOS tube; when EN is high, the M 1 pipe is turned on, the M 2 pipe is turned off, the M 3 pipe is turned off, and the M 4 pipe is turned on, at the moment, the tri-state gate is equivalent to the cascade connection of two stages of inverters, and the output signal OUT is equal to the input signal IN; when EN is low, the M 2 pipe is conducted, the M 8 pipe is cut off, the M 3 pipe is conducted, the M 7 pipe is cut off, and the output state of the tri-state gate is high resistance. Wherein the M 7、M8 pipe is an output stage and is connected to two ends of the crystal resonator; in order to drive the load capacitor with 20pF, the width-to-length ratio of the MOS tube needs to be improved, but the leakage capacity of the MOS tube is deteriorated when the width-to-length ratio is improved, so that the driving capacity and the leakage capacity need to be balanced to determine the width-to-length ratio of the MOS tube of the output stage.
The time-dependent change relation of the branch current when the crystal is injected with energy is shown in fig. 9, when the frequency of the injection signal is omega i, the amplitude is v i, the inherent frequency of the quartz crystal is omega s, and the equivalent dynamic inductance is L S, the time-dependent change formula of the current is deduced as follows:
Since the input frequency is not equal to the natural frequency, the envelope also presents sinusoidal variation based on the variation of the frequency f s, and the variation frequency of the envelope is |f s-fi |/2, so that the current envelope generates a zero point every 1/|f s-fi |, the energy injected by the quartz crystal at the zero point is counteracted to be zero, and if the injection of the energy is stopped at the moment, the effect of increasing the initial noise energy cannot be achieved. As can be seen from the graph, the current envelope amplitude reaches a maximum value when the energy injection time is 1/(2|f s-fi |). In this example, the frequency error of the second implant is 0.05% (0.006 MHz), the implant time is 83 μs at maximum, and 13.5 μs is taken down to reduce the total start-up time on the basis of satisfying amplitude; the frequency error of the first injection is less than 10% (or less than 1.2 MHz), the injection time is about 0.5 mu s or an odd multiple thereof, and 1.5 mu s is taken.
In the phase-locked loop PLL frequency locking process, the output signal of the annular voltage-controlled oscillator is shown in figure 10, the VCO output frequency is locked to 12MHz after automatic frequency calibration, and the error between the VCO output frequency and the natural frequency is about 0; the correction time in fig. 10 lasts from 3 mus to 9 mus, i.e. the PLL loop completes the frequency and phase locking within 6 mus;
fig. 11 shows simulation results of the output signal of the crystal oscillator during the secondary injection. In circuit verification, the natural frequency of the crystal resonator is 12MHz; the output signal S 2 of the XTO of the crystal oscillator is controlled by the injection signal S 1 during the first injection, and the output frequency is 11.8859MHz; the tri-state gate in the automatic frequency calibration stage presents a high resistance state, the crystal oscillator independently works, and the output frequency is 12.0012MHz; in the second injection process, the injection signal frequency is 12.0062MHz, the output frequency of the crystal oscillator after the injection is finished is 12.0005MHz, and the starting time of the crystal oscillator by adopting a secondary injection technology and a phase-locked loop technology is less than 30 mu s.
Fig. 12 shows the results of the voltage simulation across X1, X2 of the crystal resonator XTAL without the fast start module. By observing the simulation result, the starting time of the crystal oscillator without the quick start module is more than 2ms.
The phase noise of the output signal of the crystal oscillator XTO is shown in FIG. 13, and the simulation result shows that the phase noise is less than-112 dBc/Hz at 100Hz frequency offset and about-125 dBc/Hz at 1kHz frequency offset.
The foregoing is a preferred embodiment of the present invention, and the present invention should not be limited to the embodiment and the disclosure of the drawings. All equivalents and modifications that come within the spirit of the disclosure are desired to be protected.

Claims (11)

1. A quick start crystal oscillator based on a secondary injection and phase-locked loop technology is characterized in that: the digital control system comprises a crystal oscillator XTO, a phase-locked loop PLL, a tri-state gate TSG and a digital control module; the phase-locked loop circuit PLL comprises a Ring voltage-controlled oscillator Ring VCO, a phase frequency detector PFD, a charge pump CP and a low pass filter LPF; the Ring voltage-controlled oscillator Ring VCO is a three-stage pull-in current charge-discharge type Ring voltage-controlled oscillator, and is composed of a voltage-current converter and a three-stage cascaded digital inverter chain;
The connection relation of each module in the quick start crystal oscillator based on the secondary injection and phase-locked loop technology is as follows:
the crystal oscillator XTO is connected with a reference frequency input end of a phase-locked loop (PLL), an output end of the PLL is connected with a three-state gate (TSG), the three-state gate (TSG) is connected with two ends X1 and X2 of a crystal resonator (XTAL) in the crystal oscillator XTO, and the digital control module is connected with the three-state gate (TSG) and the PLL;
The Ring-shaped voltage-controlled oscillator Ring VCO in the phase-locked loop PLL is connected with the phase frequency detector PFD, the phase frequency detector PFD is connected with the charge pump CP, the charge pump CP is connected with the low-pass filter LPF, the low-pass filter LPF is connected with the Ring-shaped voltage-controlled oscillator Ring VCO, and the digital control module is connected with the phase frequency detector PFD, the charge pump CP, the low-pass filter LPF and the Ring-shaped voltage-controlled oscillator Ring VCO;
The design process based on the secondary injection technology and the phase-locked loop dependence comprises the steps of injecting energy into the crystal resonator XTAL for the first time by the Ring VCO, tracking the frequency of the phase-locked loop PLL, and injecting energy into the crystal resonator XTAL for the second time by the Ring VCO;
The method specifically comprises the following steps:
step one, the Ring VCO injects energy into the XTAL for the first time, and specifically includes the following sub-steps:
Step 1.1, under the action of a START signal START and a reset signal NRST, the digital control module outputs reset signals, the input ends V CP and V CN of the Ring voltage-controlled oscillator Ring VCO are both connected with a common mode voltage V CM, the Ring voltage-controlled oscillator Ring VCO STARTs working under the control of the reset signals, and the output frequency is close to a signal S 1 of the natural frequency of the crystal resonator;
At this time, the tri-state gate TSG is in a conducting state under the control of the digital control module, and the signal S 1 is transmitted to the two ends X1 and X2 of the crystal resonator XTAL through the tri-state gate;
Step 1.2, the crystal oscillator XTO outputs a signal S 2 with the same frequency as S 1 under the action of the signal S 1, and uses the signal S 2 as a clock signal of the digital control module;
After the first energy injection is completed, the tri-state gate TSG is switched into a high-resistance state under the time logic control of the digital control module, the Ring voltage-controlled oscillator Ring VCO is disconnected with the crystal oscillator XTO, the crystal oscillator XTO outputs a signal X 2 with smaller amplitude, higher phase noise and more stable frequency, and a clock signal S 2 with full amplitude, higher phase noise and stable frequency is obtained after the signal X 2 passes through the intermediate frequency amplifier;
step two, phase-locked loop PLL frequency tracking, specifically comprising the following sub-steps:
Step 2.1, the crystal oscillator XTO outputs a signal X 2 with smaller amplitude, relatively higher phase noise and more stable frequency after the energy is injected for the first time, the signal is amplified by an intermediate frequency amplifier to generate a square wave signal S 2, and the signal S 2 is input into a phase-locked loop PLL to be used as the reference frequency of a phase frequency detector PFD;
At this time, the phase-locked loop PLL enters a working state under the control of the digital control module, the control voltage V CP、VCN of the Ring voltage controlled oscillator Ring VCO is connected to the low pass filter LPF, and the Ring voltage controlled oscillator Ring VCO outputs an initialization signal S 1;
Step 2.2, the PFD compares the Ring VCO signal S 1 with the reference signal S 2 and outputs the phase difference pulse signals UPN, UPP, DNP and DNN in full differential form;
Pulse signals UPN, UPP, DNP and DNN control a charge pump CP to output fully differential pulse currents CON and COP to a low-pass filter LPF, under the regulation of the pulse currents, the output voltage V CP、VCN of the low-pass filter LPF is continuously changed, and the voltage V CP、VCN controls the output frequency of a Ring voltage-controlled oscillator Ring VCO to be continuously changed;
Step 2.3, under the action of automatic frequency calibration of a phase-locked loop (PLL), the output frequency of a Ring VCO is gradually locked to a desired output frequency, namely 12MHz;
After the frequency locking is completed, under the control of the digital control module, the switches D1 and D2 are disconnected, and the voltage V CP、VCN stored on the large capacitor has no charge leakage channel, so that the voltage is kept unchanged in a short time, the time of the voltage is longer than the second energy injection time, and the frequency of the Ring VCO output signal S 1 is locked;
Step three, the Ring VCO injects energy into the XTAL for the second time, specifically including the following sub-steps:
Step 3.1, the tri-state gate TSG is in a conducting state under the control of the digital control module, and the Ring VCO output signal S 1 is transmitted to the two ends X1 and X2 of the XTAL through the tri-state gate, so as to inject energy into the XTAL;
And 3.2, controlling the second energy injection time through a digital control module, switching the tri-state gate TSG to a high-resistance state after the second energy injection is completed, ending the working state of the phase-locked loop PLL, stopping the work of the phase frequency detector PFD, the charge pump CP and the Ring voltage controlled oscillator Ring VCO, resetting the output to a low potential, completing the quick start of the crystal oscillator XTO, and outputting a signal S 2 with high stability and low phase noise.
2. The fast start crystal oscillator according to claim 1, wherein the fast start crystal oscillator is based on a two-shot and phase locked loop technique, wherein: the crystal oscillator XTO is a pierce-structured three-point amplifier, implemented by low-voltage CMOS, for reducing the overall power consumption of the system.
3. The fast start crystal oscillator according to claim 1, wherein the fast start crystal oscillator is based on a two-shot and phase locked loop technique, wherein: the phase frequency detector PFD is of a fully differential structure, called a fully differential phase frequency detector, and is realized through a static CMOS logic gate circuit so as to reduce the overall power consumption of the system.
4. The fast start crystal oscillator according to claim 1, wherein the fast start crystal oscillator is based on a two-shot and phase locked loop technique, wherein: the charge pump CP is implemented using a fully differential CMOS push-pull structure, referred to as a fully differential charge pump.
5. The fast start crystal oscillator according to claim 1, wherein the fast start crystal oscillator is based on a two-shot and phase locked loop technique, wherein: the low pass filter LPF employs a third-order fully differential passive RC structure.
6. The fast start crystal oscillator according to claim 1, wherein the fast start crystal oscillator is based on a two-shot and phase locked loop technique, wherein: the tri-state gate TSG is implemented by static CMOS digital logic.
7. The fast start crystal oscillator according to claim 1, wherein the fast start crystal oscillator is based on a two-shot and phase locked loop technique, wherein: in step 1.1, the resonant frequency error of the Ring VCO output signal S 1 and the crystal resonator XTAL is less than 10%.
8. The fast start crystal oscillator according to claim 1, wherein the fast start crystal oscillator is based on a two-shot and phase locked loop technique, wherein: in step 3.1, the resonant frequency error of the Ring VCO output signal S 1 and the XTAL is less than 0.05%.
9. The fast start crystal oscillator according to claim 1, wherein the fast start crystal oscillator is based on a two-shot and phase locked loop technique, wherein: in step 3.2, the resonant frequency error between the crystal oscillator XTO output high-stability low-phase noise signal S 2 and the crystal resonator XTAL is less than 0.05%o, and the phase noise is-125 dBc/Hz at 1kHz frequency offset.
10. The fast start crystal oscillator according to claim 1, wherein the fast start crystal oscillator is based on a two-shot and phase locked loop technique, wherein: the differential PFD, CP and LPF structure not only reduces the size of the filter capacitor by more than 50%, but also reduces the conversion gain of the VCO by half, optimizes the hardware cost and noise performance of the circuit, suppresses the common mode noise of the phase-locked loop, and improves the anti-interference capability of the crystal oscillator.
11. The fast start crystal oscillator according to claim 1, wherein the fast start crystal oscillator is based on a two-shot and phase locked loop technique, wherein: optimizing the starting time of the crystal oscillator from ms level to mu s level in the secondary injection mode; the power consumption introduced by the phase-locked loop gap type low duty cycle operating mechanism is negligible.
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