CN111355451A - Up-conversion circuit - Google Patents
Up-conversion circuit Download PDFInfo
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- CN111355451A CN111355451A CN201811560359.9A CN201811560359A CN111355451A CN 111355451 A CN111355451 A CN 111355451A CN 201811560359 A CN201811560359 A CN 201811560359A CN 111355451 A CN111355451 A CN 111355451A
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
- H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing
- H03D7/16—Multiple-frequency-changing
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Abstract
The invention provides an up-conversion circuit, which comprises a local oscillator unit, a frequency mixing unit and a numerical control attenuation unit; the output end of the local oscillator unit sequentially passes through the low-pass filter and the amplifier and then is input to the frequency mixing unit together with the intermediate-frequency signal, the output end of the frequency mixing unit is connected with the input end of the numerical control attenuation unit, and the output end of the numerical control attenuation unit outputs an up-conversion signal. The up-conversion module for inhibiting the intermodulation signals realizes the frequency conversion of up-conversion through a twice frequency conversion scheme, and can effectively inhibit the intermodulation signals; the method has the advantages of high integration level, low phase noise, strong anti-interference capability and the like.
Description
Technical Field
The invention relates to the field of satellite communication systems, in particular to an up-conversion circuit.
Background
The satellite communication system comprises a receiving and communication part, wherein the down converter is mainly used for down-converting a radio frequency signal to an intermediate frequency signal so as to demodulate the intermediate frequency signal; the up-converter completes up-conversion of the intermediate frequency signal for signal transmission. For satellite system communication equipment, indexes such as gain, noise coefficient, phase noise, frequency stability and the like have important influence on the performance of the satellite communication system. The signal capacity is increased, the utilization rate of the wireless frequency spectrum is improved, and increasingly strict requirements are put forward on the performances and indexes of the frequency converter in the aspects of linearity, anti-interference capability, adaptability and the like.
In the design process of an up-conversion module, the selection of a proper frequency conversion structure is very critical, and different frequency conversion structures can influence the technical indexes, the functional indexes, the power consumption, the difficulty level, the research and development period and the production cost of a product. Therefore, it is an urgent problem to develop an up-conversion circuit.
Disclosure of Invention
The present invention provides an up-conversion circuit to solve the above technical problems.
In order to solve the technical problems, the invention adopts the technical scheme that:
an up-conversion circuit comprises a local oscillator unit, a frequency mixing unit and a numerical control attenuation unit; the output end of the local oscillator unit sequentially passes through a low-pass filter and an amplifier and then is input into a frequency mixing unit together with an intermediate frequency signal, the output end of the frequency mixing unit is connected with the input end of a numerical control attenuation unit, and the output end of the numerical control attenuation unit outputs an up-conversion signal;
the local oscillator unit comprises a phase detector PD, a voltage-controlled oscillator VOC and a programmable frequency divider, wherein one path of the voltage-controlled oscillator VOC is used as a local oscillator signal to be output, and the other path of the voltage-controlled oscillator VOC is sent to the phase detector PD to be phase-detected with an input 100MHz VCXO signal after passing through the programmable frequency divider and then fed back to a voltage control end of the VCO;
the frequency mixing unit comprises a frequency mixer and a second low-pass filter which are sequentially connected, an output signal of the amplifier and an intermediate frequency signal are input into the frequency mixer, and an output end of the second low-pass filter is connected with an input end of the numerical control attenuation unit;
the numerical control attenuation unit comprises a second radio frequency amplifier, a third attenuator, a second attenuator, a first low-pass filter, a first radio frequency amplifier and a first attenuator which are connected in sequence.
Further, the 100MHz VCXO signal is input to the phase detector PD after passing through the band pass filter.
Further, the first local oscillator frequency is 4824MHz, and the second local oscillator signal is 5774 MHz.
Further, the product model of the band-pass filter is ZBF-L70-36-3784B3A, the product model of the phase detector PD is HMC704, the product model of the voltage-controlled oscillator is ROS-5150-119+, the product model of the low-pass filter is LFCN-95, the product model of the amplifier is ERA-5SM +, the product model of the mixer is HMC219AMS8, the product model of the second low-pass filter and the first low-pass filter is LFCN-5000, the product model of the second radio-frequency amplifier is NBB-500, the product model of the third attenuator is HMC470LP3, the product models of the first attenuator and the second attenuator are PAT1220-3dB, and the product model of the first radio-frequency amplifier is NBB-310.
The invention has the advantages and positive effects that: the up-conversion module for inhibiting the intermodulation signals realizes the frequency conversion of up-conversion through a twice frequency conversion scheme, and can effectively inhibit the intermodulation signals; the method has the advantages of high integration level, low phase noise, strong anti-interference capability and the like.
Drawings
FIG. 1 is a functional block diagram of the present invention;
fig. 2 is a simulation diagram of local oscillator phase noise.
In the figure:
1. a band-pass filter; 2. a phase discriminator PD; 3. a voltage controlled oscillator; 4. a low-pass filter; 5. an amplifier; 6. a mixer; 7. a second low-pass filter; 8. a second radio frequency amplifier; 9. a third attenuator; 10. a second attenuator; 11. a first low-pass filter; 12. a first radio frequency amplifier; 13. a first attenuator; 14. a programmable frequency divider.
Detailed Description
The following detailed description of specific embodiments of the invention refers to the accompanying drawings.
As shown in fig. 1, an up-conversion circuit includes a local oscillation unit, a frequency mixing unit, and a numerical control attenuation unit; the output end of the local oscillation unit sequentially passes through the low-pass filter 4 and the amplifier 5 and then is input to the frequency mixing unit together with the intermediate frequency signal, the output end of the frequency mixing unit is connected with the input end of the numerical control attenuation unit, and the output end of the numerical control attenuation unit outputs an up-conversion signal. The local oscillator unit comprises a phase detector PD2, a voltage-controlled oscillator VOC3 and a programmable frequency divider 14, wherein one path of the voltage-controlled oscillator VOC3 is used as a local oscillator signal to be output, and the other path of the voltage-controlled oscillator VOC3 passes through the programmable frequency divider 14 and then is sent to the phase detector PD2 together with an input 100MHz VCXO signal to be output in a phase detection mode and then is fed back to a voltage control end of the VCO. The 100MHz VCXO signal is input to a phase detector PD2 after passing through a band-pass filter 1. The frequency mixing unit comprises a frequency mixer 6 and a second low-pass filter 7 which are connected in sequence, an output signal and an intermediate frequency signal of the amplifier 5 are input into the frequency mixer 6, and an output end of the second low-pass filter 7 is connected with an input end of the numerical control attenuation unit. The numerical control attenuation unit comprises a second radio frequency amplifier 8, a third attenuator 9, a second attenuator 10, a first low-pass filter 11, a first radio frequency amplifier 12 and a first attenuator 13 which are connected in sequence.
The product model of the band-pass filter 1 is ZBF-L70-36-3784B3A, the product model of the phase detector PD2 is HMC704, the product model of the voltage-controlled oscillator 3 is ROS-5150-119+, the product model of the low-pass filter 4 is LFCN-95, the product model of the amplifier 5 is ERA-5SM +, the product model of the mixer 6 is HMC219AMS8, the product model of the second low-pass filter 7 and the first low-pass filter 11 is LFCN-5000, the product model of the second radio-frequency amplifier 8 is NBB-500, the product model of the third attenuator 9 is HMC470LP3, the product models of the first attenuator 13 and the second attenuator 10 are PAT1220-3dB, and the product model of the first radio-frequency amplifier 12 is NBB-310.
This design has chooseed for use twice frequency conversion structure, through frequency conversion to 4824MHz for the first time, can make the filtering realize easily like this, and local oscillator signal can not fall on in the L wave band: otherwise, the broadband transmission signal brings many problems, such as poor image rejection, poor phase noise, false signal interference, etc., and in order to avoid these problems, two frequency conversions must be adopted. Through up-conversion, the intermediate frequency signal is up-converted to the X frequency band and then down-converted. The frequency conversion scheme solves the problems of image rejection and false interference, but the local oscillation frequency is increased, and the difficulty of local oscillation design is increased.
Due to the fact that the board card is small in size and high in circuit density, the design is mainly concerned about reducing internal intermodulation products, shielding of electromagnetic compatibility and reducing power consumption; the total power consumption of the single board can be controlled within 5W by adopting a high-efficiency power supply conversion chip, a low-power consumption radio frequency amplifier and a frequency synthesizer; to achieve small step tuning of the signal while achieving better phase noise, both LO1 and LO2 are implemented using F-N frequency synthesis techniques.
As can be seen from the schematic block diagram of the local oscillation unit, one path of the 4824MHz VCO is output as a local oscillation signal, and the other path of the VCO passes through the programmable frequency divider and then is sent to a Phase Detector (PD) together with an input 100MHz VCXO signal for phase detection output and then is fed back to a voltage control end of the VCO. An HMC704 series phase-locked component is to be employed.
A simulation of phase noise at the high-side operating frequency (7GHz) of LO1 is shown in fig. 2.
As can be seen from the simulation results: the output frequency is at 7GHz, the phase noise is-98 dbc/Hz (1kHz), and the visible phase noise of-104 dbc/Hz (10kHz) can meet the index requirement.
The phase locked loop aims to eliminate frequency errors. The principle is to eliminate the frequency difference with a phase error. When the circuit is balanced, the frequency difference can be reduced to zero, and phase tracking and frequency tracking are realized. The quality and stability of the whole machine signal mainly depend on the local oscillator; the purity of the signal depends on the choice of the local oscillator signal.
The phase noise of the local oscillator signal consists of two parts, namely a high-pass part and a low-pass part. In the high-pass part, the main determinant of its phase noise is the phase noise of the voltage controlled oscillator. For the low-pass part, the phase noise is mainly determined by the noise of each device, such as the pll chip, the reference source and the loop filter, and the frequency division ratio of the feedback branch.
In order to obtain an excellent phase noise index, a design preliminary stage is started from the aspect of device selection. And for the equipment with frequency conversion more than twice, function division is carried out, so that one local oscillator finishes large-step frequency and two local oscillators finish small-step frequency. Therefore, the frequency dividing ratio of each local oscillator of the whole machine can be reduced, so that good phase noise of the whole machine system is obtained, and the deterioration of the phase noise is reduced. Finally, the bandwidth of the phase-locked loop filter is reasonably selected, the phase noise of each device of the low-pass part in the loop and the phase noise of the voltage-controlled oscillator have an intersection point, and the frequency of the loop filter can be selected at the intersection point, so that the best phase noise index can be obtained. Phase noise is affected by other components in the loop in addition to the phase locked loop. First is the amplifier. The output signal power of the voltage-controlled oscillator is limited and the requirement of the mixer on the local oscillator signal power must be met. Meanwhile, the output signal of the voltage-controlled oscillator is input into the feedback loop through the frequency divider, which also affects the local oscillator signal power. The output power must be regulated by means of amplification, attenuation, etc. The attenuator is a passive device, so that the attenuator has little influence on phase noise and is mainly noise introduced by the amplifier. Ideally, the amplifier output signal is equal in phase noise to the input signal. Followed by a mixer. The mixer ideally experiences no degradation in phase noise across the mixer, which is the sum of the phase noise of the input signal. The power of the local and rf signals will have an effect on the phase noise, and when the power of the local and rf signals is within the required power range of the mixer, the introduced noise is zero or very low. The device selection is well done, and the power value of each stage of circuit is well controlled, so that the deterioration caused by too low power and the saturation distortion caused by too high power are prevented.
The local oscillator frequency is selected such that the reference signal frequency is 100MHz, and thus, there is also a higher harmonic of 100MHz in the reference signal. Other frequency band converters have encountered such problems: the product adopts the mode of frequency conversion twice, and the frequency down-conversion of the S frequency band radio frequency signal is to 70MHz, one intermediate frequency is 900MHz, and two local oscillator signals are 970 MHz. However, the 9 th harmonic signal of the 100MHz reference source enters into the second mixing along with the link and generates a false signal with the second local oscillator. In order to avoid similar interference signals, in the local oscillator frequency selection process, the integral multiple of 100MHz is required to be avoided, and the phenomenon that the local oscillator frequency is overlapped with the higher harmonic frequency due to the poor higher harmonic suppression of the reference signal to form a false signal is avoided. Therefore, the first local oscillator frequency is 4824MHz and the second local oscillator signal is 5774 MHz.
The frequency conversion from 70MHz to 950MHz to 2150MHz can adopt a one-time frequency conversion scheme: the frequency conversion relationship is as follows: local oscillation frequency: 1020 MHz-2120 MHz or 880 MHz-2080 MHz. Obviously, the frequency conversion scheme has a simple relationship, but the local oscillation signal falls in an L-band and cannot be filtered. Therefore, the scheme of primary frequency conversion cannot be realized, and a secondary frequency conversion mode must be adopted.
The final frequency conversion can be completed through two times of up-conversion. This makes filtering easy to implement and the local oscillator signal does not fall within the L-band. However, since the frequency after frequency conversion is very high, it is difficult to control the gain, so this solution is still not the optimal solution.
In another way, the frequency is first up-converted to the X frequency band and then down-converted, and the frequency relationship is as follows:
frequency conversion relation table:
| intermediate frequency | |
An intermediate frequency | |
|
| 70 | 4894 | 4824 | 5774 | 950 |
Therefore, the intermediate frequency is reduced to be below 8GHz, and the problem of out-of-band rejection of the mixer and the filter can be solved well. Meanwhile, MGC and amplification filtering are carried out at the frequency of 7GHz, so that the realization is easier. Therefore, the frequency conversion of up-conversion is realized by adopting a secondary frequency conversion scheme, and intermodulation signals can be effectively suppressed.
The gain indexes at all levels are distributed as follows:
a filter: fixed gain-1 dB, noise coefficient less than or equal to 1dB
A low noise amplifier: fixing the gain: 16dB, noise figure: 4dB
A mixer: frequency conversion loss: 6dB, noise figure: 6dB
An intermediate frequency filter: fixing the gain: 2dB, noise figure: 2dB
Low noise amplifier (two stage): fixing the gain: 15dB, noise figure: 4dB
A mixer: frequency conversion loss: 6dB, noise figure: 6dB
A low noise amplifier: fixing the gain: 22dB, noise figure: 4dB
A local oscillation frequency: 4824MHz
Output power: not less than 15dBm
Phase noise: -85dBc/1kHz
Second local oscillator frequency: 5774 MHz-6974 MHz
Output power: not less than 13dBm
Phase noise: -85dBc/1kHz
The local oscillator has two implementation modes: one form is the PDRO local oscillator, which is generally adopted for high frequency local oscillators in order to achieve better phase noise figure. However, the local oscillator in the form has the defects of poor stability, high design difficulty and design cost, narrow bandwidth and difficulty in realizing 1400MHz bandwidth; the other is a normal PLL version. The local oscillator has good stability and high reliability, adopts the design of an integrated chip and has a simple circuit structure. With the improvement of the maturity of the design of the integrated circuit, the radio frequency chip, especially the PLL chip and the VCO chip, has good phase noise indexes, good stability and reliability, and the bandwidth reaches an octave. The schematic diagram is shown in the figure.
The main limiting factor of the common PLL type local oscillator is the phase noise of the VCO. At present, the phase noise of the VCO with the frequency of 7GHz can reach-115 dBc/Hz @100KHz, and the index can meet the design requirement in the technical scheme.
The up-conversion module for inhibiting the intermodulation signals realizes the frequency conversion of 70MHz-L frequency band signals through twice frequency conversion, and has high integration level, low phase noise and strong anti-interference capability. Because the devices for realizing the frequency conversion and amplification functions are nonlinear devices, interference signals such as harmonic signals, intermodulation signals and the like can be generated. At the same time, a large number of signals of different frequency bands exist in space. These signals generate interference signals through intermodulation, frequency multiplication, etc., and the interference signals affect the demodulation accuracy. In order to eliminate or reduce interference signals, filtering technology is required to filter radio frequency signals and variable frequency link signals during reasonable frequency spectrum processing, so that the purity of the signals is improved.
The embodiments of the present invention have been described in detail, but the description is only for the preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made within the scope of the present invention should be covered by the present patent.
Claims (4)
1. An up-conversion circuit, characterized by: the device comprises a local oscillation unit, a frequency mixing unit and a numerical control attenuation unit; the output end of the local oscillator unit sequentially passes through a low-pass filter and an amplifier and then is input into a frequency mixing unit together with an intermediate frequency signal, the output end of the frequency mixing unit is connected with the input end of a numerical control attenuation unit, and the output end of the numerical control attenuation unit outputs an up-conversion signal;
the local oscillator unit comprises a phase detector PD, a voltage-controlled oscillator VOC and a programmable frequency divider, wherein one path of the voltage-controlled oscillator VOC is used as a local oscillator signal to be output, and the other path of the voltage-controlled oscillator VOC is sent to the phase detector PD to be phase-detected with an input 100MHz VCXO signal after passing through the programmable frequency divider and then fed back to a voltage control end of the VCO;
the frequency mixing unit comprises a frequency mixer and a second low-pass filter which are sequentially connected, an output signal of the amplifier and an intermediate frequency signal are input into the frequency mixer, and an output end of the second low-pass filter is connected with an input end of the numerical control attenuation unit;
the numerical control attenuation unit comprises a second radio frequency amplifier, a third attenuator, a second attenuator, a first low-pass filter, a first radio frequency amplifier and a first attenuator which are connected in sequence.
2. An up-conversion circuit according to claim 1, characterized in that: the 100MHz VCXO signal is input to the phase discriminator PD after passing through the band-pass filter.
3. An up-conversion circuit according to claim 1 or 2, characterized in that: the first local oscillator frequency is 4824MHz, and the second local oscillator signal is 5774 MHz.
4. An up-conversion circuit according to claim 1, characterized in that: the product model of the band-pass filter is ZBF-L70-36-3784B3A, the product model of the phase detector PD is HMC704, the product model of the voltage-controlled oscillator is ROS-5150-.
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| CN201811560359.9A CN111355451A (en) | 2018-12-20 | 2018-12-20 | Up-conversion circuit |
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|---|---|---|---|
| CN201811560359.9A CN111355451A (en) | 2018-12-20 | 2018-12-20 | Up-conversion circuit |
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| CN111355451A true CN111355451A (en) | 2020-06-30 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114237343A (en) * | 2021-12-24 | 2022-03-25 | 中国电子科技集团公司第十四研究所 | Ultra-wideband waveform generation method based on dual-channel DAC |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114237343A (en) * | 2021-12-24 | 2022-03-25 | 中国电子科技集团公司第十四研究所 | Ultra-wideband waveform generation method based on dual-channel DAC |
| CN114237343B (en) * | 2021-12-24 | 2023-09-08 | 中国电子科技集团公司第十四研究所 | Ultra-wideband waveform generation method based on dual-channel DAC |
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