WO2018090686A1 - Frequency synthesizer - Google Patents

Abstract

Provided is a frequency synthesizer, comprising a phase-locked loop module (10), a loop filter (20) and a voltage-controlled oscillator module (30). The voltage-controlled oscillator module (30) comprises a plurality of voltage-controlled oscillation units (310, 320, 330). The voltage-controlled oscillation unit comprises a resonant circuit (311) composed of a plurality of discrete electronic components and a switch control circuit (313) which are electrically connected. Resonance parameters of each resonant circuit are different, which in turn generates resonant frequencies of different frequency ranges. By composing the plurality of voltage-controlled oscillation units from a plurality of discrete electronic components, the cost is reduced, and the resonance parameters in the resonant circuit can also be adjusted to output signals with different frequency bands. With the plurality of voltage-controlled oscillation units, the frequency synthesis of segment frequency ranges with non-overlap seamless convergence is realized, and phase noise of a frequency-synthesized output signal is reduced.

Description

Frequency synthesizer

[Technical Field]

This invention relates to frequency synthesis techniques, and more particularly to frequency synthesizers.

【Background technique】

Frequency synthesis technology is one of the key technologies for achieving high performance indicators in electronic systems such as radar and communication, due to the phase noise of the frequency synthesizer (Phase Noise) affects many indicators of the receiving and transmitting system, such as the selectivity of the adjacent channel received and the power ratio of the adjacent channel transmitted. When the receiving and transmitting bands are wide, the phase noise of the frequency synthesizing part generally deteriorates sharply. This deterioration is mainly a voltage controlled oscillator (Voltage). Controlled Oscillator, VCO).

For the wide-band receiving and transmitting local oscillator part of the voltage-controlled oscillator, mainly using a single broadband integrated voltage-controlled oscillator chip provided by foreign RF IC manufacturers or using a plurality of narrow-band dedicated integrated voltage-controlled oscillators for synthetic design, but this The two integrated voltage-controlled oscillators are expensive, typically costing hundreds of dollars or even thousands, and the frequency output of their voltage-controlled oscillators is not adjustable.

[Summary of the Invention]

Based on this, it is necessary to provide a frequency synthesizer with low-cost, frequency-synthesizable frequency synthesis with adjustable output frequency range and seamless integration.

A frequency synthesizer comprising:

a phase locked loop module receives an external control signal and outputs a tuning voltage;

a loop filter connected to the phase locked loop module for filtering AC noise in the phase locked loop module;

a voltage controlled oscillator module, comprising a multi-stage voltage controlled oscillation unit whose output frequency ranges do not overlap each other; wherein

The voltage-controlled oscillating unit includes an electrically connected resonant circuit and a switch control circuit composed of discrete components; the resonant circuit is respectively connected to the phase-locked loop module and the loop filter to form a phase-locked loop; The resonant parameters of the resonant circuit are different, and the resonant circuit is configured to generate a resonant frequency output according to the tuning voltage and the resonant parameter; and the switch control circuit is configured to control power supply of the resonant circuit.

The frequency synthesizer includes a phase locked loop module, a loop filter, and a voltage controlled oscillator module, wherein the voltage controlled oscillator module comprises a multi-stage voltage controlled oscillation unit. The voltage controlled oscillating unit includes an electrically connected resonant circuit and a switch control circuit composed of a plurality of discrete electronic components. The resonant parameters of each of the resonant circuits are different, which in turn produces resonant frequencies that resonate in different frequency ranges. The multi-stage voltage-controlled oscillating unit composed of a plurality of discrete electronic components has low cost, can also adjust the resonance parameter in the resonant circuit, and outputs signals having different frequency bands. Through the multi-stage voltage-controlled oscillating unit, the frequency synthesis in which the segment frequency ranges are not overlapped and seamlessly connected is realized, and the phase noise of the frequency composite output signal is also reduced.

In one embodiment, the resonant circuit includes a first capacitor, a second capacitor, a first inductor, and a transistor;

The first capacitor and the second capacitor are connected in parallel;

a collector of the transistor is coupled to the switch control circuit; an emitter of the transistor is coupled to ground; a base of the transistor is coupled to a first end of the first capacitor;

One end of the first inductor is respectively connected to the second end of the first capacitor and the phase locked loop module, and the other end of the first inductor is grounded.

In one embodiment, the resonant circuit further includes a first diode, a second diode, a third diode, and a fourth diode;

An anode of the first diode is respectively connected to an anode of the second diode and a first inductor; a cathode of the first diode is respectively connected to a cathode of the second diode and a cathode of the third diode The cathode of the fourth diode and the phase-locked loop module are connected; the anode of the third diode and the anode of the fourth diode are both grounded.

In one embodiment, the voltage controlled oscillating unit further includes a filter circuit, an input end of the filter circuit is connected to the phase locked loop module, and an output end of the filter circuit is connected to the resonant circuit.

In one embodiment, the voltage controlled oscillating unit further includes a feedback circuit, the feedback circuit includes a fourth capacitor, a fifth capacitor, and a sixth capacitor; one end of the fourth capacitor is connected to a base of the transistor The other end of the fourth capacitor is grounded via the sixth capacitor; one end of the fifth capacitor is connected to a common end of the fourth capacitor and the sixth capacitor, and the other end of the fifth capacitor is The emitter of the transistor is connected.

In one embodiment, the voltage controlled oscillating unit further includes a seventh capacitor for suppressing a low frequency spur signal, one end of the seventh capacitor being connected to a collector of the transistor, and the other of the seventh capacitor One end is connected to the phase locked loop module.

In one embodiment, the loop filter is a third-order passive filter, and an input end of the third-order passive filter is connected to the phase-locked loop module, and the third-order passive filter The output ends are respectively connected to the plurality of segments of the voltage controlled oscillation unit.

In one embodiment, a low pass filter is further included, and an input end of the low pass filter is connected to each of the plurality of voltage controlled oscillation units, and an output end of the low pass filter and the phase locked loop module connection.

In one of the embodiments, the number of the voltage controlled oscillating units is three.

In one embodiment, the three voltage controlled oscillation units output frequency ranges of 720 to 780 MHz, 780 to 840 MHz, and 840 to 900 MHz.

[Description of the Drawings]

1 is a structural block diagram of a frequency synthesizer in an embodiment;

2 is a circuit schematic diagram of a loop filter in an embodiment;

3 is a circuit schematic diagram of a voltage controlled oscillation unit in an embodiment;

4 is a circuit schematic diagram of a low pass filter in an embodiment.

 【detailed description】

In order to facilitate the understanding of the present invention, the present invention will be described more fully hereinafter with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the understanding of the present disclosure will be more fully understood.

All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. The terminology used in the description of the present invention is for the purpose of describing particular embodiments and is not intended to limit the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

As shown in FIG. 1 , the frequency synthesizer includes a phase locked loop module 10 , a loop filter 20 , and a voltage controlled oscillator module 30 . The voltage controlled oscillator module 30 includes multi-stage voltage control. The oscillating units 310, 320, 330. The voltage controlled oscillating unit 310 includes a resonant circuit 311 and a switch control circuit 313 which are electrically connected and composed of a plurality of discrete electronic components. The resonant circuit 311 is respectively connected to the phase locked loop module 10 and the loop filter 20 to form a phase locked loop. The switch control circuit 313 controls the power supply of the resonant circuit 311, and only one segment of the voltage controlled oscillating unit 310 operates at the same time, and does not affect each other. The resonance parameters of each of the resonant circuits 311 are different, and the resonant circuit 311 can generate resonance frequencies of different frequency ranges according to the tuning voltages and different resonance parameters. The multi-stage voltage-controlled oscillating unit 310 is composed of a plurality of discrete electronic components, which is low in cost, can also adjust the resonance parameters in the resonance circuit 311, and output signals having different frequency bands. The multi-stage voltage-controlled oscillating unit 310 realizes frequency synthesis in which the segment frequency ranges do not overlap each other and seamlessly connects, and also reduces the phase noise of the frequency composite output signal.

In an embodiment, the phase-locked loop module 10 includes a phase-locked loop chip, a frequency divider, and a phase detector. The phase-locked loop chip uses Skyworks' Sky72310 as a single-channel output fractional phase-locked loop, and the reference clock is 19.2 MHz. The pump current is 1000μA and the pump voltage is 5V. The phase-locked loop module 10 receives the external control signal, and outputs the tuning voltage to the multi-stage voltage-controlled oscillating unit 310 after being filtered by the loop filter 20. After being processed by the voltage controlled oscillation unit 310, the output RF signal is fed back to the phase locked loop chip. The phase-locked loop chip indirectly compares the received RF signal with the reference clock frequency to form a phase-locked loop, thereby obtaining a stable and reliable frequency signal.

The loop filter 20 is connected to the phase-locked loop module 10 for filtering the AC noise of the frequency divider and the phase detector output of the phase-locked loop module 10. In this implementation, the loop filter 20 is a third-order passive filter. Referring to FIG. 2, the input end of the third-order passive filter is connected to the phase-locked loop module 10, and the third-order passive filtering The output ends of the devices are respectively connected to a plurality of segments of the voltage controlled oscillation unit 310. Of course, in other embodiments, the loop filter 20 can also select different types of filters according to actual requirements, and is not limited to the third-order passive filter.

The voltage controlled oscillator module 30 includes a multi-stage voltage controlled oscillating unit 310 whose output frequency ranges do not overlap each other. In this embodiment, the voltage controlled oscillator module 30 includes a three-stage voltage-controlled oscillating unit, which is a high-band voltage-controlled oscillating unit 310, a mid-band voltage-controlled oscillating unit 320, and a low-band voltage-controlled oscillating unit 330.

The voltage controlled oscillating unit 310 includes an electrically connected resonant circuit 311 and a switch control circuit 313. Referring to FIG. 3, the resonant circuit 311 includes a first capacitor C1, a second capacitor C2, a first inductor L1, and a transistor Q1. The inductance of the first inductor L1 in each voltage-controlled oscillating unit 310 is different. The capacitance values of the second capacitor C2 are also the same, that is, each voltage-controlled oscillation unit 310 has a different resonance parameter. The transistor Q1 in the voltage-controlled oscillating unit 310 is an NPN-type silicon epitaxial transistor Q1, which has the characteristics of wideband and low noise.

The first capacitor C1 and the second capacitor C2 are connected in parallel. The collector of the transistor Q1 is connected to the switch control circuit 313; the emitter of the transistor Q1 is grounded; and the base of the transistor Q1 is connected to the first end of the first capacitor C1. One end of the first inductor L1 is respectively connected to the second end of the first capacitor C1 and the phase locked loop module 10, and the other end of the first inductor L1 is grounded. The resonant circuit 311 further includes a first diode D1, a second diode D2, a third diode, and a fourth diode, wherein the first diode D1, the second diode D2, and the third Diode D3 and fourth diode D4 are both varactor diodes. The anode of the first diode D1 is respectively connected to the anode of the second diode D2 and the first inductor L1; the cathode of the first diode D1 and the cathode of the second diode D2 and the third The cathode of the diode D3, the cathode of the fourth diode D4, and the phase-locked loop module 10 are connected; the anode of the third diode D3 and the anode of the fourth diode D4 are both grounded.

The voltage controlled oscillating unit 310 further includes a filter circuit 315, and an input end of the filter circuit 315 is connected to the phase locked loop module 10; an output end of the filter circuit 315 is connected to the resonant circuit 311.

The tuning voltage signal sent by the phase-locked loop module 10 is filtered by the loop filter 20 and filtered by the inductor L3, and then sent to the high-band voltage-controlled oscillating unit 310, the mid-band voltage-controlled oscillating unit 310, and the low-band voltage-controlled oscillating unit 310, respectively. The voltage-controlled oscillating unit 310 includes a resonant circuit 311 and a switch control circuit 313. The switch control circuit 313 controls the peripheral circuit to supply power to the resonant circuit 311, so that the voltage-controlled oscillating unit 310 starts to operate, and only one piece of the voltage-controlled oscillating unit 310 operates at the same time.

The tuning voltage signal is filtered by the filter circuit 315 and sent to the resonant circuit 311, wherein the tuning voltage ranges from 0 to 5V. The varactor diode (D1, D2, D3, D4) PN junction capacitance value in the resonance circuit 311 varies with the value of the voltage applied across it. The difference in voltage value causes a change in the resonant frequency. In order to prevent the tuning voltage from drifting due to high temperature, low temperature, etc., the tuning voltages of the high-frequency voltage-controlled oscillating unit 310, the mid-band voltage-controlled oscillating unit 310, and the low-band voltage-controlled oscillating unit 310 all operate in the range of 1.5 to 3.5V. There is a margin between the upper and lower ends of the voltage to ensure that the tuning voltage does not exceed 0-5V in case of high and low temperature, and 100% locking is guaranteed.

Taking the high-frequency voltage-controlled oscillating unit 310 as an example, when the tuning voltage is 1.5V, the high-frequency voltage-controlled oscillating unit 310 is adjusted by adjusting the values of the first capacitor C1, the second capacitor C2, and the first inductor L1 of the resonating portion. The frequency of the output is 840MHz; when the tuning voltage is 3.5V, the output frequency of the high-frequency voltage-controlled oscillating unit 310 is 900MHz, so that the frequency-controlled oscillation unit 310 is realized when the tuning voltage is changed within the range of 1.5-3.5V. The output frequency varies from 840MHz to 900MHz. Because the resonance parameters of the first capacitor C1, the second capacitor C2, and the first inductor L1 in the resonant circuit 311 can be adjusted, the voltage-controlled oscillating unit 310 can output frequencies of different frequency bands, so that the frequency synthesis is more flexible and adapts to different Band requirements.

Correspondingly, by setting the resonance parameters (capacitance and inductance value) of the first capacitor, the second capacitor, and the first inductor in the resonant circuit 311 of the intermediate frequency voltage-controlled oscillating unit 320 and the low-frequency voltage-controlled oscillating unit 330, the intermediate frequency voltage control can be ensured. The resonance points of the oscillation unit 320 and the low-frequency voltage-controlled oscillation unit 330 do not overlap and seamlessly engage. In this embodiment, the frequency range of the intermediate frequency voltage controlled oscillation unit 320 is 780~840 MHz; the frequency range of the low frequency voltage control oscillation unit 330 is 720~780 MHz. The frequency of the frequency output by each voltage-controlled oscillating unit is only 60MHz, which greatly reduces the phase noise pressure of the voltage-controlled oscillating unit.

Table 1-1 Voltage Control Oscillator Frequency Allocation Table

 VCO frequency range  VCO_H (high section)  840~900MHz  VCO_M (middle section)  780~840MHz  VCO_L (low section)  720~780MHz

The above-mentioned frequency synthesizer using a multi-segment discrete device can realize ultra-wideband frequency synthesis with a band width of 180 MHz, a center frequency of 810 MHz and a relative bandwidth of 22.22%, and the cost is low, and the phase noise can also be satisfied. Requirements.

In an embodiment, the voltage controlled oscillating unit 310 further includes a feedback circuit 317, and the feedback circuit 317 includes a fourth capacitor C4, a fifth capacitor C5, and a sixth capacitor C6. One end of the fourth capacitor C4 is connected to the base of the transistor Q1, and the other end of the fourth capacitor C4 is grounded via the sixth capacitor C6; one end of the fifth capacitor C5 and the fourth capacitor C4, the common terminal of the sixth capacitor C6 is connected, and the other end of the fifth capacitor C5 is connected to the emitter of the transistor Q1. Through the capacitance of the feedback circuit 317, the resonance condition of the resonant circuit 311 is assisted, thereby affecting the amplitude value and phase noise of the output signal.

In an embodiment, the voltage controlled oscillating unit 310 further includes a seventh capacitor C7 for suppressing low frequency spurs. One end of the seventh capacitor C7 is connected to the collector of the transistor Q1, and the other end of the seventh capacitor C7 is connected to the phase locked loop module 10. In practical applications, an external operational amplifier is used to amplify the output signal after the frequency synthesizer, and the seventh capacitor C7 (2pF) can be used to suppress the low-frequency spurious signal and prevent the operational amplifier from amplifying the low-frequency signal.

The frequency synthesizer further includes a low pass filter 40. Referring to FIG. 4, the input end of the low pass filter 40 is connected to the plurality of segments of the voltage controlled oscillating unit 310, and the output of the low pass filter 40 is The phase locked loop module 10 is connected. The output signal of the multi-stage voltage-controlled oscillating unit 310 is filtered by the low-pass filter 40, and then input to the phase-locked loop module 10 to form a loop.

The technical features of the above-described embodiments may be arbitrarily combined. For the sake of brevity of description, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be considered as the scope of this manual.

The above-described embodiments are merely illustrative of several embodiments of the present invention, and the description thereof is more specific and detailed, but is not to be construed as limiting the scope of the invention. It should be noted that a number of variations and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be determined by the appended claims.

Claims (10)

A frequency synthesizer, comprising: a phase locked loop module receives an external control signal and outputs a tuning voltage; a loop filter connected to the phase locked loop module for filtering AC noise in the phase locked loop module; a voltage controlled oscillator module, comprising a multi-stage voltage controlled oscillation unit whose output frequency ranges do not overlap each other; wherein The voltage-controlled oscillating unit includes an electrically connected resonant circuit and a switch control circuit composed of discrete components; the resonant circuit is respectively connected to the phase-locked loop module and the loop filter to form a phase-locked loop; The resonant parameters of the resonant circuit are different, and the resonant circuit is configured to generate a resonant frequency output according to the tuning voltage and the resonant parameter; and the switch control circuit is configured to control power supply of the resonant circuit. The frequency synthesizer according to claim 1, wherein the resonant circuit comprises a first capacitor, a second capacitor, a first inductor, and a transistor; The first capacitor and the second capacitor are connected in parallel; a collector of the transistor is coupled to the switch control circuit; an emitter of the transistor is coupled to ground; a base of the transistor is coupled to a first end of the first capacitor; One end of the first inductor is respectively connected to the second end of the first capacitor and the phase locked loop module, and the other end of the first inductor is grounded. The frequency synthesizer according to claim 2, wherein said resonant circuit further comprises a first diode, a second diode, a third diode, and a fourth diode; An anode of the first diode is respectively connected to an anode of the second diode and a first inductor; a cathode of the first diode is respectively connected to a cathode of the second diode and a cathode of the third diode The cathode of the fourth diode and the phase-locked loop module are connected; the anode of the third diode and the anode of the fourth diode are both grounded. The frequency synthesizer according to claim 1, wherein the voltage-controlled oscillating unit further comprises a filter circuit, wherein an input end of the filter circuit is connected to the phase-locked loop module; and an output end of the filter circuit The resonant circuit is connected. The frequency synthesizer according to claim 2, wherein the voltage controlled oscillating unit further comprises a feedback circuit, wherein the feedback circuit comprises a fourth capacitor, a fifth capacitor and a sixth capacitor; and one end of the fourth capacitor Connected to a base of the transistor, the other end of the fourth capacitor is grounded via the sixth capacitor; one end of the fifth capacitor is connected to a common end of the fourth capacitor and the sixth capacitor, The other end of the five capacitors is coupled to the emitter of the transistor. The frequency synthesizer according to claim 2, wherein said voltage controlled oscillation unit further comprises a seventh capacitance for suppressing low frequency spurious signals, one end of said seventh capacitance being connected to a collector of said transistor The other end of the seventh capacitor is connected to the phase locked loop module. The frequency synthesizer according to claim 1, wherein the loop filter is a third-order passive filter, and an input end of the third-order passive filter is connected to the phase-locked loop module. The output ends of the third-order passive filter are respectively connected to a plurality of segments of the voltage-controlled oscillating unit. The frequency synthesizer according to claim 1, further comprising a low pass filter, wherein the input end of the low pass filter is connected to the plurality of segments of the voltage controlled oscillating unit, and the output of the low pass filter The end is connected to the phase locked loop module. The frequency synthesizer according to claim 1, wherein the number of the voltage controlled oscillation units is three. The frequency synthesizer according to claim 9, wherein the three voltage-controlled oscillation units output frequency ranges of 720 to 780 MHz, 780 to 840 MHz, and 840 to 900 MHz.