CN105356878A - Realization method and apparatus of improved three-ring bandwidth frequency synthesizer - Google Patents

Abstract

The invention discloses a realization method and apparatus of an improved three-ring bandwidth frequency synthesizer, for improving a reference ring, a coarse adjusting ring and an addition ring of a three-ring bandwidth frequency synthesizer. The reference ring is improved in such a way that harmonic wave components of reference signals are directly extracted and filtered and amplified and thusaddition of one phase-lock type frequency synthesizer on the basis of a conventional scheme is omitted; loop low-pass filters in the addition ring and the coarse adjusting ring are improved in such a way that a passive proportion integration low-pass filter is added to an addition circuit, a part of component values of original loop filters are modified, and the transfer function of the improved loop filters is the same as that of the original loop filters; and the far-end phase noise of a voltage controlled oscillator (VCO) of the addition ring is improved in such a way that a broadband VCO in a traditional addition ring is replaced by use of multiple narrowband VCOs. The method and apparatus have the advantages of low cost, low power consumption, low phase noise, low stray, low loss, small volume and easy integration.

Description

A kind of implementation method of three ring width band frequency synthesizers of improvement and device

Technical field

The present invention relates to microwave/millimeter wave device arts, is a kind of implementation method and device that can be widely used in the frequency synthesizer of broadband test instrument.

Background technology

Wideband frequency synthesizer is a kind of important module that can be widely used in the instruments such as vector signal source, frequency spectrograph, vector network analyzer, channel simulator, and this module needs to provide low phase noise, wide band local vibration source to instrument.The reference frequency output of frequency synthesizer, phase noise performance directly determine the performance index of instrument.Therefore the method for designing of the frequency synthesizer of broadband, Low phase noise, low cost, low spurious is particularly important.

Summary of the invention

The object of this invention is to provide a kind of implementation method and device of three ring width band frequency synthesizers of improvement, there is the feature of Low phase noise, broadband, low spurious, can the cost of lowering apparatus and power consumption greatly.

For achieving the above object, the technical solution used in the present invention is:

An implementation method for three ring width band frequency synthesizers of improvement, the reference rings of three ring width band frequency synthesizers, coarse adjustment ring and addition ring are improved as follows:

Improvement for reference rings: on the basis of former reference rings, is changed to ten frequency multipliers of low noise and the combination of band pass filter by 1GHz phase-locked loop, namely 1GHz is produced by 100MHz signal direct frequency doubling;

Improvement for addition ring and coarse adjustment ring intermediate ring road low pass filter: adopt the method for D/A converter DAC preset adjustment voltage controlled oscillator VCO to carry out secondary ring locking, and passive proportion integrating low-pass filter is added after loop filter add circuit, keep loop filter transfer function identical with former loop filter, therefore the exponent number of whole loop and state can be made to remain unchanged;

Improvement for the voltage controlled oscillator VCO far-end phase noise of addition ring: 3 ~ 6GHz wideband voltage controlled oscillator VCO is changed to N number of bandwidth is narrower, the linearity and the better voltage controlled oscillator VCO of phase noise performance, and add radio-frequency (RF) switch to carry out the switching of voltage controlled oscillator VCO; The loop bandwidth of design addition ring is less than the loop bandwidth of coarse adjustment ring module.

Concrete methods of realizing for the improvement of the addition ring in three ring frequency synthesizers and coarse adjustment ring intermediate ring road low pass filter is: be added with the output voltage of loop filter by the add circuit of Design of Amplifiers, act on the voltage tuning end of voltage controlled oscillator VCO, the now output voltage of D/A converter DAC tuning voltage controlled oscillator VCO vibration, near required output frequency, makes cycle of phase-locked loop can catch and lock; Want loop-locking, the initial oscillation f of D/A converter DAC preset adjustment voltage controlled oscillator VCO _vCOfollowing two conditions should be met:

f _MIX-f _REF<f _VCO<f _MIX+f _REF

|f _OUT-f _VCO|<△f _LP

Wherein, f _mIXmixing incoming frequency, f _rEFreference input frequency, f _oUTthe loop output frequency needed, △ f _lPbeing loop filter frequency tuning range, is the function of the output voltage range of loop filter and the tuning sensitivity of VCO;

The phase discriminator used due to coarse tuning loop is the structure of difference output, therefore the design of loop filter adopts active differential loop filter structure;

The output voltage of active differential loop filter is added with the output voltage of D/A converter DAC through add circuit, acts on the tuning end of voltage controlled oscillator VCO; If the transfer function of add circuit is A (s), then the transfer function of loop filter can be expressed as

$F\left(s\right)=\frac{R_2{C}_{2}s+1}{R_1{C}_{2}s(R_3{C}_{3}s+1)}\&CenterDot;A\left(s\right)$

After add circuit, add passive proportion integrating low-pass filter, and revise former loop filter subelement value; This loop filter is on the basis of former loop filter, and a resistance of having connected after add circuit is R ₂resistance, and a parallel connection resistance is R ₄resistance and capacitance be C ₂capacitances in series combination, define a passive proportion integrating low-pass filter, and the resistance of the resistance of two in former loop filter by R ₂change R into ₂+ R ₄; The transfer function of this loop filter can be expressed as

$F\left(s\right)=\frac{(R_2+R_4)C_{2}s+1}{R_1{C}_{2}s(R_3{C}_{3}s+1)}\&CenterDot;A\left(s\right)\&CenterDot;\frac{R_2{C}_{2}s+1}{(R_2+R_4)C_{2}s+1}=\frac{R_2{C}_{2}s+1}{R_1{C}_{2}s(R_3{C}_{3}s+1)}\&CenterDot;A\left(s\right)$

Above two formulas of contrast, the loop filter transfer function after improvement is identical with former loop filter, therefore the exponent number of whole loop and state can be made to remain unchanged.

A kind of implement device of three ring width band frequency synthesizers of improvement, comprise reference rings, coarse adjustment ring and addition ring, described reference rings comprises constant-temperature crystal oscillator, ten frequency multipliers, band pass filter, frequency divider, the programmable frequency divider of connecting successively, and programmable frequency divider is connected with a band pass filter and three low pass filters by one pole four throw switch; Comprise loop low pass filter in described addition ring and coarse adjustment ring, loop low pass filter is connected with add circuit, and add circuit is connected with passive proportion integrating low-pass filter; Described addition ring comprises adder, and adder is connected with several voltage controlled oscillator VCO, and several voltage controlled oscillator VCO are switched by radio-frequency (RF) switch.

The invention has the beneficial effects as follows:

The present invention proposes a kind of method for designing of three ring width band frequency synthesizers of improvement, the method is improved reference rings, coarse adjustment ring and the addition ring in traditional three ring frequency synthesizers, has low cost, low-power consumption, Low phase noise, low spurious, low-power consumption, small size be easy to integrated advantage.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of existing reference rings;

Fig. 2 is the schematic diagram of the reference rings that the present invention improves;

Fig. 3 is the schematic diagram of existing addition ring active loop filter;

Fig. 4 is the schematic diagram of the addition ring active loop filter that the present invention improves;

Fig. 5 is the improvement project of addition ring VCO far-end phase noise of the present invention;

Fig. 6 is many rings frequency synthesizer of phase locking structured flowchart.

Embodiment

Below in conjunction with specific embodiment, the present invention is further described.

Three ring phase-locked Frequency Synthesis Technique Controlled are hybrid frequency synthetic technologys of integrated use pll frequency synthesizer and Direct Digital Frequency Synthesizer Technology, have that output frequency resolution rate is high, reference frequency output is wide and the advantage such as output frequency phase noise is low, be usually used in high performance radio frequency or microwave signal generator.

As shown in Figure 6, three ring frequency synthesizers are made up of fine tuning ring, coarse adjustment ring and addition ring three phase-locked loops.Wherein, coarse adjustment ring is operated in the working frequency range of synthesizer, provides the upper frequency of large stepping to export, to realize the performance index of high operate frequency and wide reference frequency output; The output of fine tuning ring is after rearmounted frequency divider, and working frequency range equals the output frequency increment of coarse adjustment ring, provides the lower frequency of little stepping to export, to realize the performance index of high output frequency resolution rate; Finally by addition ring, the output of these two parts is added up.The working frequency range of this frequency synthesizer depends on coarse adjustment ring, and output frequency resolution rate depends on fine tuning ring.

The fine tuning ring of three ring frequency synthesizer of phase locking and coarse adjustment ring are all classical phase-locked loop frequency synthesizer structures, VCO due to fine tuning ring exports and have passed through frequency divider, phase noise is improved, and the output phase noise of usual fine tuning ring is much better than the phase noise of coarse adjustment ring.Addition ring is then different from general phase-locked loop structures, is the mixing structure phase-locked loop that feedback loop inserts frequency mixer, analyzes, can draw total output phase noise θ to the phase noise characteristic of mixing structure phase-locked loop through row _no(s) be:

${\mathrm{\&theta;}}_{no}\left(s\right)=\&lsqb;{\mathrm{\&theta;}}_{ni}\left(s\right)+{\mathrm{\&theta;}}_{mi}\left(s\right)-{\mathrm{\&theta;}}_m+\frac{V_{PD}\left(s\right)}{K_D}\&rsqb;t\left(s\right)+\frac{V_{LF}\left(s\right)}{K_D}\&CenterDot;\frac{T\left(s\right)}{H\left(s\right)}+{\mathrm{\&theta;}}_{nv}\left(s\right)\&lsqb;1-T\left(s\right)\&rsqb;---\left(1\right)$

Wherein, θ _nis () is equivalent reference input phase noise, V _pDs () is phase discriminator output voltage noise, V _lFs () is loop filter output voltage noise, θ _nvs () is that VCO exports phase noise, θ _ms () is the phase noise that frequency mixer itself is introduced, θ _mis () is the phase noise of mixer-input signal, K _dit is closed loop transfer function, T (s) of the discriminator sensitivity of phase discriminator, phase-locked loop frequency synthesizer.

The output phase noise that mixing structure phase-locked loop is total, the part within loop bandwidth determines primarily of the phase noise of reference source, mixed frequency input signal, phase discriminator and frequency mixer; Part beyond loop bandwidth then determines primarily of the phase noise of VCO.

Compared with classical phase-locked loop structures, export phase noise and export phase noise decision primarily of coarse adjustment ring in the band of mixing structure phase-locked loop, the outer phase noise that exports of band then determines primarily of the VCO phase noise of addition ring.For the feature of hybrid ring, the present invention is proposing improved plan with reference to changing, on coarse adjustment ring and addition ring:

Improvement for reference rings: as Fig. 1 and Fig. 2, on the basis of former scheme, is changed to ten frequency multipliers of low noise and the combination of band pass filter by 1GHz phase-locked loop, namely 1GHz is produced by 100MHz signal direct frequency doubling.Nowadays, the phase noise specifications of the high-performance OCXO product on market can reach-130dBc/Hz100Hz ,-159dBc/Hz1kHz ,-170dBc/Hz10kHz ,-175dBc/Hz100kHz ,-178dBc/Hz1MHz, in theory, if use this OCXO, 1GHz to export phase noise preferably can reach-110dBc/Hz100Hz ,-139dBc/Hz1kHz ,-150dBc/Hz10kHz ,-155dBc/Hz100kHz ,-158dBc/Hz1MHz.The near-end phase noise of the characteristic reference module of traditional reference rings is determined to the in-band phase noise of final addition ring module output signal, adopt the method, make referrer module have excellent phase noise performance, the demand of system can be met well.

Improvement for the addition ring in three ring frequency synthesizers and coarse adjustment ring intermediate ring road low pass filter: enter Fig. 3 and Fig. 4, the method of D/A converter DAC preset adjustment voltage controlled oscillator VCO is adopted to carry out secondary ring locking, and proposed after loop filter adder the method adding passive proportion integrating low-pass filter, the method keeps loop filter transfer function identical with former loop filter, therefore the exponent number of whole loop and state can be made to remain unchanged.

Concrete methods of realizing is added with the output voltage of loop filter by the add circuit of Design of Amplifiers, act on the voltage tuning end of voltage controlled oscillator VCO, the now output voltage of D/A converter DAC tuning voltage controlled oscillator VCO vibration, near required output frequency, makes cycle of phase-locked loop can catch and lock.Want loop-locking, the initial oscillation f of D/A converter DAC preset adjustment voltage controlled oscillator VCO _vCOfollowing two conditions should be met:

f _MIX-f _REF<f _VCO<f _MIX+f _REF(2)

|f _OUT-f _VCO|<△f _LP(3)

Wherein, f _mIXmixing incoming frequency, f _rEFreference input frequency, f _oUTthe loop output frequency needed, △ f _lPbeing loop filter frequency tuning range, is the function of the output voltage range of loop filter and the tuning sensitivity of voltage controlled oscillator VCO.

The phase discriminator used due to coarse tuning loop is the structure of difference output, therefore the design of loop filter have employed active differential loop filter structure.

The output voltage of active differential loop filter is added with the output voltage of D/A converter DAC through add circuit, acts on the tuning end of voltage controlled oscillator VCO, and therefore, add circuit can regard a part for loop filter as.If the transfer function of add circuit is A (s), then the transfer function of loop filter can be expressed as

$F\left(s\right)=\frac{R_2{C}_{2}s+1}{R_1{C}_{2}s(R_3{C}_{3}s+1)}\&CenterDot;A\left(s\right)---\left(4\right)$

In object test, find that the outer phase noise of output signal band has obvious deterioration compared to the phase noise of VCO, mainly caused by DAC preset adjustment voltage with the noise that add circuit is introduced, therefore, consider that adding one-stage low-pass filter at adder output carrys out filtered voltage noise, to improve phase noise.But, add filter and loop can be made to change, increase the exponent number of loop, make loop become unstable.

In order to the exponent number that keeps loop original and state, the present invention proposes and adopted after add circuit the method adding passive proportion integrating low-pass filter, and revise the method for former loop filter subelement value, its structure as shown in Figure 4.This loop filter is on the basis of former loop filter, and a resistance of having connected after adder is R ₂resistance, and a parallel connection resistance is R ₄resistance and capacitance be C ₂capacitances in series combination, define a passive proportion integrating low-pass filter, and the resistance of the resistance of two in former loop filter by R ₂change R into ₂+ R ₄.The transfer function of this loop filter can be expressed as

$F\left(s\right)=\frac{(R_2+R_4)C_{2}s+1}{R_1{C}_{2}s(R_3{C}_{3}s+1)}\&CenterDot;A\left(s\right)\&CenterDot;\frac{R_2{C}_{2}s+1}{(R_2+R_4)C_{2}s+1}=\frac{R_2{C}_{2}s+1}{R_1{C}_{2}s(R_3{C}_{3}s+1)}\&CenterDot;A\left(s\right)---\left(5\right)$

Contrast (4) and formula (5), can find out, the loop filter transfer function after improvement is identical with former loop filter, therefore the exponent number of whole loop and state can be made to remain unchanged.

Improvement for the voltage controlled oscillator VCO far-end phase noise of addition ring: in the band of addition ring module, output phase noise determines primarily of the output phase noise of mixed frequency input signal, also namely determine by exporting phase noise in coarse adjustment ring modular belt, the outer phase noise that exports of band then determines primarily of voltage controlled oscillator VCO.But addition changes and usually adopts wideband voltage controlled oscillator VCO, and its linearity and phase noise performance are all undesirable, and generally, the bandwidth of voltage controlled oscillator VCO is narrower, and its linearity and phase noise performance can be better.Therefore, export phase noise performance outward to improve system band, the addition ring module that the present invention proposes as shown in Figure 5 is improved one's methods.3 ~ 6GHz wideband voltage controlled oscillator VCO, on the basis of former scheme, has been changed to that N number of bandwidth is narrower, the linearity and the better voltage controlled oscillator VCO of phase noise performance by the method, and adds radio-frequency (RF) switch SPNT to carry out the switching of voltage controlled oscillator VCO.The loop bandwidth of design addition ring module is less than the loop bandwidth of coarse adjustment ring module, effectively can improve the phase noise near loop bandwidth and beyond loop bandwidth.

A kind of implement device of three ring width band frequency synthesizers of improvement, comprise reference rings, coarse adjustment ring and addition ring, as shown in Figure 2, reference rings comprises constant-temperature crystal oscillator OCXO, ten frequency multipliers, band pass filter BPF, frequency divider, the programmable frequency divider of connecting successively, and programmable frequency divider is connected with an a band pass filter BPF and three low pass filter LPF by one pole four-throw switch S P4T.Comprise loop low pass filter in addition ring and coarse adjustment ring, as shown in Figure 4, loop low pass filter is connected with add circuit, and add circuit is connected with passive proportion integrating low-pass filter.Addition ring comprises adder, and adder is connected with several voltage controlled oscillator VCO, and several voltage controlled oscillator VCO are switched by radio-frequency (RF) switch.

The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (3)

1. the implementation method of three ring width band frequency synthesizers improved, is characterized in that: improve as follows the reference rings of three ring width band frequency synthesizers, coarse adjustment ring and addition ring:

Improvement for reference rings: on the basis of former reference rings, is changed to ten frequency multipliers of low noise and the combination of band pass filter by 1GHz phase-locked loop, namely 1GHz is produced by 100MHz signal direct frequency doubling;

Improvement for addition ring and coarse adjustment ring intermediate ring road low pass filter: adopt the method for D/A converter DAC preset adjustment voltage controlled oscillator VCO to carry out secondary ring locking, and passive proportion integrating low-pass filter is added after loop filter add circuit, keep loop filter transfer function identical with former loop filter, therefore the exponent number of whole loop and state can be made to remain unchanged;

Improvement for the voltage controlled oscillator VCO far-end phase noise of addition ring: 3 ~ 6GHz wideband voltage controlled oscillator VCO is changed to N number of bandwidth is narrower, the linearity and the better voltage controlled oscillator VCO of phase noise performance, and add radio-frequency (RF) switch to carry out the switching of voltage controlled oscillator VCO; The loop bandwidth of design addition ring is less than the loop bandwidth of coarse adjustment ring module.

2. the implementation method of the three ring width band frequency synthesizers improved as claimed in claim 1, it is characterized in that: the concrete methods of realizing for the improvement of the addition ring in three ring frequency synthesizers and coarse adjustment ring intermediate ring road low pass filter is: be added with the output voltage of loop low pass filter by the add circuit of Design of Amplifiers, act on the voltage tuning end of voltage controlled oscillator VCO, the now output voltage of D/A converter DAC tuning voltage controlled oscillator VCO vibration, near required output frequency, makes cycle of phase-locked loop can catch and lock; Want loop-locking, the initial oscillation f of D/A converter DAC preset adjustment voltage controlled oscillator VCO _vCOfollowing two conditions should be met:

f _MIX-f _REF<f _VCO<f _MIX+f _REF

|f _OUT-f _VCO|<△f _LP

Wherein, f _mIXmixing incoming frequency, f _rEFreference input frequency, f _oUTthe loop output frequency needed, △ f _lPbeing loop filter frequency tuning range, is the function of the output voltage range of loop filter and the tuning sensitivity of VCO;

The phase discriminator used due to coarse tuning loop is the structure of difference output, therefore the design of loop filter adopts active differential loop filter structure;

The output voltage of active differential loop filter is added with the output voltage of D/A converter DAC through add circuit, acts on the tuning end of voltage controlled oscillator VCO; If the transfer function of add circuit is A (s), then the transfer function of loop filter can be expressed as

$F\left(s\right)=\frac{R_2{C}_{2}s+1}{R_1{C}_{2}s(R_3{C}_{3}s+1)}\&CenterDot;A\left(s\right)$

After add circuit, add passive proportion integrating low-pass filter, and revise former loop filter subelement value; This loop filter is on the basis of former loop filter, and a resistance of having connected after add circuit is R ₂resistance, and a parallel connection resistance is R ₄resistance and capacitance be C ₂capacitances in series combination, define a passive proportion integrating low-pass filter, and the resistance of the resistance of two in former loop filter by R ₂change R into ₂+ R ₄; The transfer function of this loop filter can be expressed as

$F\left(s\right)=\frac{(R_2+R_4)C_{2}s+1}{R_1{C}_{2}s(R_3{C}_{3}s+1)}\&CenterDot;A\left(s\right)\&CenterDot;\frac{R_2{C}_{2}s+1}{(R_2+R_4)C_{2}s+1}=\frac{R_2{C}_{2}s+1}{R_1{C}_{2}s(R_3{C}_{3}s+1)}\&CenterDot;A\left(s\right)$

Above two formulas of contrast, the loop filter transfer function after improvement is identical with former loop filter, therefore the exponent number of whole loop and state can be made to remain unchanged.

3. the implement device of the three ring width band frequency synthesizers improved, comprise reference rings, coarse adjustment ring and addition ring, it is characterized in that: described reference rings comprises constant-temperature crystal oscillator, ten frequency multipliers, band pass filter, frequency divider, the programmable frequency divider of connecting successively, programmable frequency divider is connected with a band pass filter and three low pass filters by one pole four throw switch; Comprise loop low pass filter in described addition ring and coarse adjustment ring, loop low pass filter is connected with add circuit, and add circuit is connected with passive proportion integrating low-pass filter; Described addition ring comprises adder, and adder is connected with several voltage controlled oscillator VCO, and several voltage controlled oscillator VCO are switched by radio-frequency (RF) switch.