CN218829900U - Circuit for improving phase demodulation leakage stray suppression of phase-locked loop - Google Patents
Circuit for improving phase demodulation leakage stray suppression of phase-locked loop Download PDFInfo
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Abstract
The utility model discloses a circuit for improving phase-locked loop phase demodulation leakage stray suppression belongs to phase-locked loop frequency synthesis technical field. The method comprises the following steps: the input end of the phase discriminator is used for receiving a reference signal; the input end of the annular filter is electrically connected with the output end of the phase discriminator; the input end of the voltage-controlled oscillator is electrically connected with the output end of the ring filter; the output end of the voltage-controlled oscillator outputs stable radio-frequency signals and is also electrically connected with the input end of the phase discriminator; and at least one group of LC low-pass filtering units connected in series are externally connected with the annular filter. The utility model discloses guaranteeing under the requirement of use occasion to phase-locked loop frequency modulation time, can obviously improve the suppression effect that loop filter leaked spurious suppression to the phase discrimination, and whole LC low pass filter's simple structure, convenient to use, economical type is high.
Description
Technical Field
The utility model belongs to the technical field of the phase-locked loop frequency synthesis, in particular to be used for one kind to improve phase-locked loop phase demodulation leakage stray suppression's circuit.
Background
The phase-locked loop frequency synthesis technology is widely applied to the technical fields of communication, radar, navigation, measurement, automatic control and space, and provides local oscillation signals for a radar transmitting system and an electronic receiving system. The phase-locked loop frequency synthesis circuit is a closed-loop phase error control system, and a typical phase-locked loop circuit consists of a phase discriminator, a loop filter (including an active loop filter or a passive loop filter) and a voltage-controlled oscillator.
The phase-locked loop filter loop plays a low-pass role in noise of the input reference signal, the phase discriminator and the frequency divider and plays a high-pass role in noise of the voltage-controlled oscillator, so that the noise of the input reference signal, the phase discriminator and the frequency divider can be effectively suppressed when the value of the filter loop bandwidth is small, and the noise of the voltage-controlled oscillator is effectively suppressed when the value of the filter loop bandwidth is large; the loop bandwidth of the phase-locked loop is generally 1/5-1/20 of the phase detection frequency, and the loop bandwidth can affect the phase detection leakage stray of the radio frequency output signal and the locking time of the radio frequency output. The suppression of the ring filter to the phase detection leakage stray in the phase-locked loop circuit is related to the loop bandwidth of the phase-locked loop, and the wider the loop bandwidth of the phase-locked loop is, the weaker the suppression capability of the phase detection leakage stray is, and the stronger the suppression capability of the phase detection leakage stray is otherwise. When designing a loop filter, the loop bandwidth should be comprehensively analyzed and selected according to the suppression requirements for different noises.
The loop bandwidth of the phase-locked loop is generally determined by the phase demodulation frequency of the phase-locked loop, and the too narrow loop can influence the frequency hopping time of the phase-locked loop, so that the loop bandwidth of the phase-locked loop cannot be reduced without limit in order to improve the phase demodulation leakage stray suppression in the phase-locked loop design process. The traditional loop filter has better inhibition on phase discrimination leakage stray, and can achieve more than 60 dBc; when the phase-locked loop has high phase-locked loop leakage suppression (more than 70 dBc) and the frequency hopping time is required, the loop bandwidth of the phase-locked loop cannot be narrowed greatly, so that the application problem of the traditional loop filter in the occasion with high phase-locked loop leakage spurious suppression requirement cannot be solved effectively.
SUMMERY OF THE UTILITY MODEL
The utility model discloses a solve the technical problem who exists among the above-mentioned background art, provide a circuit for improving phase-locked loop phase demodulation leakage stray suppression.
The utility model adopts the following technical scheme: a circuit for improving phase-locked loop phase-detection leakage spur rejection, comprising:
the input end of the phase discriminator is used for receiving a reference signal;
the input end of the annular filter is electrically connected with the output end of the phase discriminator;
the input end of the voltage-controlled oscillator is electrically connected with the output end of the ring filter; the output end of the voltage-controlled oscillator outputs stable radio-frequency signals and is also electrically connected with the input end of the phase discriminator;
wherein, the loop filter is externally connected with at least one group of LC low-pass filter units which are mutually connected in series.
Through the technical scheme, the annular filter is connected with at least one group of LC low-pass filtering units in series, so that the suppression effect of phase demodulation leakage stray suppression of the phase-locked loop is increased as much as possible under the condition that certain requirements on the frequency hopping time of the phase-locked loop are ensured.
In a further embodiment, the loop filter is an active loop filter.
In a further embodiment, the loop filter is a passive loop filter.
In a further embodiment, the LC low-pass filtering units are each provided with a transmission zero point; when the number of the LC low-pass filtering units is one, the transmission zero is connected with the active annular filter;
when the number of the LC low-pass filtering units is at least two, the LC low-pass filtering unit close to the phase discriminator is defined as the first LC low-pass filtering unit, the corresponding transmission zero point is connected with the active annular filter, and the other LC low-pass filtering units are connected in series by taking the transmission zero point as an input end.
Through the technical scheme, the output signal at the specific frequency is strongly inhibited.
In a further embodiment, the loop filter comprises: the filter comprises a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a resistor R1, a resistor R2, a resistor R3 and a filter A1;
one end of the resistor R1 is connected with the output end of the phase discriminator, and the other end of the resistor R1 is connected with the positive input of the filter A1; the negative electrode input of the filter A1 is connected with a reference voltage, the output end of the filter A1 is connected with one end of a resistor R3, and the other end of the resistor R3 is connected with the input end of the voltage-controlled oscillator; the filter further comprises a resistor R2, one end of the resistor R2 is connected with the anode input of the filter A1, the other end of the resistor R2 is connected with a capacitor C2, the other end of the capacitor C2 is connected with the output end of the filter A1, and two ends of a capacitor C3 are connected with two ends of the resistor R2 in parallel; one end of the capacitor C1 is connected with the output end of the phase discriminator, and the other end of the capacitor C1 is grounded; one end of the capacitor C4 is connected with the input end of the voltage-controlled oscillator, and the other end is grounded.
Through the technical scheme, the basic structure of the loop filter is designed, and the effect of the loop filter is to process the basic phase discrimination leakage stray suppression.
In a further embodiment, the LC low-pass filtering unit includes: a capacitor C5, a capacitor C6, a capacitor C7 and an inductor L1;
the connection relationship is that a capacitor C5 is connected with an inductor L1 in parallel, one end of the parallel connection is connected with the other end of a resistor R3 in the annular filter, and the other end of the parallel connection is connected with the input end of the voltage-controlled oscillator; one end of the capacitor C6 is connected with the input ends connected in parallel, and the other end of the capacitor C is grounded; one end of the capacitor C6 is connected with the output end which is connected in parallel, and the other end of the capacitor C6 is grounded; one end of the capacitor C5 connected in parallel with the inductor L1 is a position affecting a first transmission zero point.
Through the technical scheme, the suppression effect of the LC low-pass filtering unit on the whole annular filter is further enhanced.
In a further embodiment, the LC low-pass filtering units may be connected in series, and the input end of the LC low-pass filtering unit, whose capacitor and inductor form a parallel circuit, is connected to the output end of the LC low-pass filtering unit of the previous stage.
According to the technical scheme, according to the actual use condition, in order to meet the requirement of the annular filter on the suppression of the transmission zero point near a certain frequency, the suppression effect is enhanced by connecting a plurality of groups of LC low-pass filtering units in series.
In a further embodiment, the capacitors C4 and C6 are equivalently replaced by one capacitor, and the grounded capacitor of the output end of the LC low-pass filter unit of the previous stage and the grounded capacitor of the input end of the LC low-pass filter unit of the next stage can be equivalently replaced by one capacitor.
Through the technical scheme, according to the actual use effect, the capacitors are combined, the structure of the whole circuit is simplified, and the equipment cost of the whole circuit is reduced.
The utility model has the advantages that: the utility model discloses an improve loop filter of phase-locked loop phase demodulation leakage stray suppression, including active loop filter or passive loop filter, be provided with at least a set of LC low pass filter unit on active loop filter or the passive loop filter, LC low pass filter unit includes the LC low pass filter of at least one transmission zero point, and LC low pass filter's first transmission zero point is near phase demodulation frequency; according to the requirement of the use occasion on phase detection leakage stray suppression, a plurality of LC low-pass filtering units can be connected in series; compared with the traditional phase-locked loop active loop filter, the phase-locked loop active loop filter connected in series with the LC low-pass filtering unit can obviously improve the suppression effect of the loop filter on phase demodulation leakage stray suppression under the condition of ensuring the requirement of a use occasion on the frequency modulation time of the phase-locked loop, and the whole LC low-pass filter has the advantages of simple structure, convenience in use and high economy.
Drawings
Fig. 1 is a schematic block diagram of the basic components of a phase-locked loop circuit.
Fig. 2 is a conventional phase-locked loop active loop filter.
Fig. 3 is a phase-locked loop active loop filter in series with a one-stage LC low-pass filtering unit.
Fig. 4 is a phase locked loop active loop filter cascaded into a two stage LC low pass filter unit.
Detailed Description
Example 1
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the examples of the present invention. As shown in fig. 1, a typical phase-locked loop circuit is composed of a phase detector, a loop filter (including an active loop filter or a passive loop filter), and a voltage-controlled oscillator, wherein the phase detector compares phases of a reference input signal and a feedback radio frequency signal to provide a phase-detection error voltage or current; after filtering processing is carried out by the annular filter, a relatively stable voltage value is generated to control the output frequency of the voltage-controlled oscillator, finally, the frequency of the feedback radio frequency signal is synchronous with the frequency of the input reference signal to enter a loop locking state, and the voltage-controlled oscillator outputs stable radio frequency after the loop is locked. The loop filter is an important component of the phase-locked loop, is connected in series between the phase discriminator and the voltage-controlled oscillator, plays important roles of maintaining loop stability, controlling loop in-band and out-band noise, suppressing sideband stray interference and the like, and is the key of the design of the frequency synthesizer of the phase-locked loop.
In this embodiment, an active ring filter is taken as an example for explanation; as shown in fig. 2, the loop filter includes: the filter comprises a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a resistor R1, a resistor R2, a resistor R3 and a filter A1;
one end of the resistor R1 is connected with the output end of the phase discriminator, and the other end of the resistor R1 is connected with the positive input of the filter A1; the negative electrode input of the filter A1 is connected with a reference voltage, the output end of the filter A1 is connected with one end of a resistor R3, and the other end of the resistor R3 is connected with the input end of the voltage-controlled oscillator; the filter further comprises a resistor R2, one end of the resistor R2 is connected with the anode input of the filter A1, the other end of the resistor R2 is connected with a capacitor C2, the other end of the capacitor C2 is connected with the output end of the filter A1, and two ends of a capacitor C3 are connected with two ends of the resistor R2 in parallel; one end of the capacitor C1 is connected with the output end of the phase discriminator, and the other end of the capacitor C1 is grounded; one end of the capacitor C4 is connected with the input end of the voltage-controlled oscillator, and the other end is grounded. The traditional active ring filter has better inhibition on phase discrimination leakage stray, and can achieve more than 60 dBc; when the phase-locked loop has high phase-locked loop leakage suppression (more than 70 dBc) and the frequency hopping time is required, the loop bandwidth of the phase-locked loop cannot be narrowed greatly, so that the application problem of the traditional loop filter in the occasion with high phase-locked loop leakage spurious suppression requirement cannot be solved effectively.
Example 2
Based on the fact that the application problem of the traditional active ring filter in the embodiment 1 in the occasion with high requirements on phase-locked loop phase demodulation leakage stray suppression is difficult to solve, in the implementation, an LC low-pass filtering unit is arranged to enhance the suppression effect; the specific implementation mode is that the LC low-pass filtering unit at least comprises one transmission zero point, and the first transmission zero point is positioned near the phase discrimination frequency; as shown in fig. 3, the LC low pass filter unit includes: a capacitor C5, a capacitor C6, a capacitor C7 and an inductor L1; the connection relationship is that a capacitor C5 is connected with an inductor L1 in parallel, one end of the parallel connection is connected with the other end of a resistor R3 in the annular filter, and the other end of the parallel connection is connected with the input end of the voltage-controlled oscillator; one end of the capacitor C6 is connected with the input ends connected in parallel, and the other end of the capacitor C is grounded; one end of the capacitor C6 is connected with the output end which is connected in parallel, and the other end of the capacitor C6 is grounded; one end of the capacitor C5 connected in parallel with the inductor L1 is a position affecting a first transmission zero point. In order to ensure the suppression effect of the LC low-pass filtering unit on the active annular filter, a plurality of LC low-pass filtering units can be connected in series to enhance the effect; the LC low-pass filtering units may be connected in series, and the input end of the parallel circuit formed by the capacitor and the inductor is connected to the output end of the upper LC low-pass filtering unit, in this embodiment, taking the phase-locked loop active loop filter of the two LC low-pass filtering units as an example, as shown in the connection relationship in fig. 4, the LC low-pass filtering units have the same structure, and the common requirement is that: the transmission zero of an LC low-pass filter consisting of a capacitor C5, a capacitor C6, a capacitor C7 and an inductor L1 is positioned near the phase discrimination frequency of the phase-locked loop; meanwhile, the influence of the LC low-pass filter on the phase margin of the original source loop is required to be as small as possible. The transmission zero of an LC low-pass filter consisting of a capacitor C8, a capacitor C9, a capacitor C10 and an inductor L2 is positioned near the phase discrimination frequency of the phase-locked loop; meanwhile, the influence of the phase margin introduced by the LC low-pass filter on the original source loop is required to be as small as possible.
Example 3
Combine embodiment 1 and embodiment 2 right the utility model discloses suppression effect when in actual use carries out contrast detection to phase-locked loop output 2 ~ 2.8GHz verifies the circuit as the example, and phase-locked loop reference input frequency is 100MHz, sets up the inside phase demodulation frequency of phase-locked loop and is 10MHz, and radio frequency output actual measurement 2GHz and 2.8GHz. The operational amplifier selected by the loop filter is THS4031ID of TI company, and values of the resistor, the capacitor and the inductor under different filter loop states are shown in Table 1.
The corresponding phase discrimination leakage spurious suppression of 10MHz is shown in table 2
TABLE 1 values of resistance, capacitance and inductance of a phase-locked loop filter
| Road stateAnd testing frequency point | Phase-discriminated leakageStray rejection @2GHz | Phase demodulation leakageStray rejection @2.8GHz |
| Conventional active loop circuit | 61.8dBc | 61.7dBc |
| Cascade 1-stage LC filter circuit | 72.1dBc | 71.5dBc |
| Cascade 2-stage LC filter circuit | 94.7dBc | 85.8dBc |
TABLE 2 comparison of phase-discrimination leakage spurious rejection by different loop filters at the same output frequency
The preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, however, the present invention is not limited to the details of the above embodiments, and the technical concept of the present invention can be modified to perform various equivalent transformations, which all belong to the protection scope of the present invention.
Claims (8)
1. A circuit for improving phase detector leakage spur rejection in a phase locked loop, comprising:
the input end of the phase discriminator is used for receiving a reference signal;
the input end of the annular filter is electrically connected with the output end of the phase discriminator;
the input end of the voltage-controlled oscillator is electrically connected with the output end of the ring filter; the output end of the voltage-controlled oscillator outputs stable radio-frequency signals and is also electrically connected with the input end of the phase discriminator;
and at least one group of LC low-pass filtering units connected in series are externally connected with the annular filter.
2. The circuit of claim 1, wherein the loop filter is an active loop filter.
3. The circuit for improving phase detection leakage spur rejection of a phase locked loop of claim 1, wherein the loop filter is a passive loop filter.
4. The circuit for improving phase-locked loop phase-demodulation leakage stray rejection of claim 2, wherein the LC low-pass filtering units are each provided with a transmission zero; when the number of the LC low-pass filtering units is one, the transmission zero is connected with the active annular filter;
when the number of the LC low-pass filtering units is at least two, the LC low-pass filtering unit close to the phase discriminator is defined as the first LC low-pass filtering unit, the corresponding transmission zero point is connected with the active annular filter, and the other LC low-pass filtering units are connected in series by taking the transmission zero point as an input end.
5. A circuit for improving phase detection leakage spur rejection in a phase locked loop as claimed in claim 2, wherein said loop filter comprises: the filter comprises a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a resistor R1, a resistor R2, a resistor R3 and a filter A1;
one end of the resistor R1 is connected with the output end of the phase discriminator, and the other end of the resistor R1 is connected with the positive input of the filter A1; the negative electrode input of the filter A1 is connected with a reference voltage, the output end of the filter A1 is connected with one end of a resistor R3, and the other end of the resistor R3 is connected with the input end of the voltage-controlled oscillator; the filter also comprises a resistor R2, wherein one end of the resistor R2 is connected with the anode input of the filter A1, the other end of the resistor R2 is connected with a capacitor C2, the other end of the capacitor C2 is connected with the output end of the filter A1, and two ends of a capacitor C3 are connected with two ends of the resistor R2 in parallel; one end of the capacitor C1 is connected with the output end of the phase discriminator, and the other end of the capacitor C1 is grounded; one end of the capacitor C4 is connected with the input end of the voltage-controlled oscillator, and the other end is grounded.
6. The circuit of claim 5, wherein the LC low-pass filtering unit comprises: a capacitor C5, a capacitor C6, a capacitor C7 and an inductor L1;
the connection relationship is that a capacitor C5 is connected with an inductor L1 in parallel, one end of the parallel connection is connected with the other end of a resistor R3 in the annular filter, and the other end of the parallel connection is connected with the input end of the voltage-controlled oscillator; one end of the capacitor C6 is connected with the input ends connected in parallel, and the other end of the capacitor C is grounded; one end of the capacitor C6 is connected with the output ends connected in parallel, and the other end of the capacitor C is grounded; one end of the capacitor C5 connected in parallel with the inductor L1 is a position affecting a first transmission zero point.
7. The circuit according to claim 6, wherein the LC low-pass filtering unit is capable of connecting multiple sets thereof in series, and an input end of a parallel circuit formed by a capacitor and an inductor is connected to an output end of a previous LC low-pass filtering unit.
8. The circuit according to claim 6, wherein the capacitors C4 and C6 are equivalently replaced by a single capacitor, and a ground capacitor at an output terminal of the LC low-pass filtering unit of the previous stage and a ground capacitor at an input terminal of the LC low-pass filtering unit of the next stage are equivalently replaced by a single capacitor.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202221637904.1U CN218829900U (en) | 2022-06-24 | 2022-06-24 | Circuit for improving phase demodulation leakage stray suppression of phase-locked loop |
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| CN202221637904.1U CN218829900U (en) | 2022-06-24 | 2022-06-24 | Circuit for improving phase demodulation leakage stray suppression of phase-locked loop |
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