RU2774401C1 - Hybrid multi-ring frequency synthesizer - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention relates to radio engineering and can be used in measuring technology, radar and communications. The hybrid multi-ring frequency synthesizer contains a reference frequency oscillator, a frequency-phase detector, an annular low-pass filter, a voltage-controlled oscillator, a directional coupler, a frequency divider, a mixer, a frequency multiplier, a digital computational synthesizer and a bandpass filter, a second mixer, a second bandpass filter, a third band pass filter, a second frequency divider, a second phase locked loop, and a third frequency divider. The second output of the reference frequency generator is connected to the input of the frequency multiplier. The first output of the reference frequency generator is connected to the input of the second phase locked loop. The first output of the frequency multiplier is connected to the first input of the second mixer. The second output of the frequency multiplier is connected to the input of a digital computational synthesizer, the output of which is connected through a band-pass filter to the second input of the second mixer. The output of the second mixer through the second band-pass filter is connected to the second input of the first mixer, the output of which is connected through a frequency divider to the second input of the frequency-phase detector. The output of the second ring of phase locked loop through the third frequency divider is connected to the first input of the frequency-phase detector. The output of the frequency-phase detector is connected to the input of a directional coupler through a ring low-pass filter and a voltage-controlled generator connected in series. The second output of the directional coupler is connected to the first input of the first mixer through the second frequency divider and the third band-pass filter connected in series. The first output of the directional coupler is the output of the proposed hybrid multi-ring synthesizer.

EFFECT: reducing the level of phase noise and side spectral components of the output oscillation of the synthesizer.

1 cl, 5 dwg

Description

Technical field

The invention relates to radio engineering and can be used in measuring technology, radar and communications.

Prior Art

A multi-ring synthesizer is known (Dan H. Wolaver. Phase-Locked Loop Circuit Design. Prentice Hall, 1991), in which the reduction of spurious components and obtaining a small frequency tuning step is achieved using three phase-locked loops with a mixer, one of which provides accurate frequency setting , the second phase-locked loop is a coarse frequency setting, and the third phase-locked loop is the summation of frequencies to obtain the frequency of the output oscillation of the synthesizer.

The disadvantage of this solution is the high level of phase noise in the phase-locked loop for coarse frequency setting, which actually determines the level of phase noise of the output oscillation of the entire synthesizer.

A digital computational synthesizer and a hybrid synthesizer combining a digital computational synthesizer and a phase-locked loop are known (patent US 6483388 A1 24.01.2002). The hybrid synthesizer uses a mixer to convert the reference frequency generated by the reference source and the signal generated by the digital compute synthesizer, the output of the mixer is connected to the input of a phase-locked loop in which the frequency of the mixer output signal is multiplied to the frequency of the output signal of the synthesizer.

The first disadvantage of this synthesizer is the impossibility of obtaining a low level of phase noise and discrete components determined by the comparison frequency of the phase detector and the frequency division factor in the phase locked loop ring. The second disadvantage of this synthesizer is the narrow frequency range at the mixer output, limited from above by half the clock frequency of the digital computational synthesizer.

Known frequency synthesizer (patent RU 2523188 C1 07/20/2014), including a reference oscillator, the output of which is connected to a frequency multiplier, a frequency converter, a frequency divider, the output of which is connected to the input of a frequency-phase detector, the output of which is connected to the input of the error signal filter, the output which is connected to the input of a controlled generator, providing an increase in the frequency resolution and spectral purity of the output signal by connecting the output of the frequency multiplier to the input of an additional frequency multiplier, the output of which is connected to the input of the frequency divider, the output of which is connected to the reference input of the frequency-phase detector.

The disadvantage of this solution is the need to obtain a high multiplication factor of the frequency multiplier to obtain small phase noise of the output oscillation of the frequency synthesizer and the impossibility of obtaining a fractional multiplication factor of the frequency multiplier.

A hybrid frequency synthesizer is known (patent RU 172814 U1 07/25/2017) with improved spectral characteristics, containing a reference frequency oscillator with two outputs, a frequency-phase detector with two inputs and an output connected through a ring low-pass filter to a voltage-controlled generator, output which is the output of the entire device and is connected through a directional coupler to one of the inputs of the mixer, one of the outputs of the reference frequency generator is connected through a frequency multiplier to a digital computational synthesizer, the output of which is connected through a band-pass filter to the second input of the mixer, the output of which is connected through a frequency divider with one from the inputs of the frequency-phase detector, also containing an additional digital computational synthesizer having a clock input, which is connected to the second output of the reference frequency generator, and an output connected to the second input of the frequency-phase detector, which makes it possible to expand the frequency tuning range the output signal of the device and reduce the level of side components of the spectrum of the output signal of the device (Fig. one).

The disadvantage of this solution is the high level of phase noise of the output oscillation, determined by the intrinsic noise of the digital computational synthesizer and the ratio of the frequency of the output oscillation of the digital computational synthesizer and the frequency of the output oscillation of the frequency multiplier. This is due to the fact that the phase noise of the output oscillation of a digital computational synthesizer increases with an increase in the output frequency of a digital computational synthesizer, including those operating on fundamental frequency images in the second, third, and higher Nyquist zones [1].

The second disadvantage of this solution is the presence of discrete spectral components in the spectrum of the output oscillation of a digital computational synthesizer, the filtering of which is difficult when tuning the frequency of the output oscillation of a digital computational synthesizer in a wide frequency band.

The essence of the invention

The technical problem of the claimed invention is to solve these shortcomings of the closest analogue.

The technical result is to reduce the level of phase noise and side spectral components of the output oscillation of the synthesizer.

The essence of the claimed invention lies in the fact that in a hybrid multi-ring frequency synthesizer containing a reference frequency oscillator, a frequency-phase detector, an annular low-pass filter, a voltage-controlled oscillator, a directional coupler, a frequency divider, a mixer, a frequency multiplier, a digital computational synthesizer and band-pass filter, a second mixer, a second band-pass filter, a third band-pass filter, a second frequency divider, a second phase-locked loop and a third frequency divider are additionally introduced, while the second output of the reference frequency generator is connected to the input of the frequency multiplier, the first output of the reference frequency generator is connected to the input of the second phase-locked loop, the frequency divider has two outputs, where the first output of the frequency multiplier is connected to the first input of the second mixer, the second output of the frequency multiplier is connected to the input of a digital computational synthesizer, the output is connected through a bandpass filter to the second input of the second mixer, the output of the second mixer through the second band-pass filter is connected to the second input of the first mixer, the output of which is connected through the first frequency divider to the second input of the frequency-phase detector, the output of the second phase-locked loop through the third frequency divider is connected to the first frequency input -phase detector, the output of the frequency-phase detector through a series-connected low-pass ring filter and a voltage-controlled generator is connected to the input of a directional coupler, the second output of the directional coupler through a second frequency divider and a third band-pass filter connected in series is connected to the first input of the first mixer, the first the output of the directional coupler is the output of the proposed hybrid multi-ring synthesizer.

The claimed invention is illustrated on graphic materials, where

Figure 1 - prior art

Figure 2 shows a block diagram of the proposed hybrid multi-ring synthesizer, where:

1 - reference frequency oscillator (GKOCH), 3 - frequency-phase detector (FPD), 4 - ring low-pass filter (LPF), 5 - voltage controlled oscillator (VCO), 6 - directional coupler (NO), 7 - first frequency divider (DF1), 8 - first mixer (SM1), 9 - frequency multiplier (MF), 10 - digital computational synthesizer (DCS), 11 - first band pass filter (PF1), 12 - second mixer (SM2), 13 - second bandpass filter (PF2), 14 - third bandpass filter (PF3), 15 - second frequency divider (DF2) 16 - second phase locked loop (PLL2), 17 - third frequency divider (DF3).

Figure 3 - phase noise of a digital computational synthesizer at a frequency f _DDS

Figure 4 - spectrum of fluctuations at the first input SM1 pos.8 in figure 2

Figure 5 - spectrum of fluctuations at the first input of the mixer of the prior art

The proposed hybrid multi-ring synthesizer contains GOFC 1, which has two outputs, the first output of GOFC 1 is connected to the input of PLL2 16, the second output of GOFC 1 is connected to the input of FA 9, the output of PLL2 16 is connected to the first input of DC3 17, the output of DC3 17 is connected to the first input of FFD 3 , the output of PFD 3 through serially connected low-pass filter 4, VCO 5, is connected to NO 6, the first output of NO 6 is the output of a hybrid multi-ring synthesizer, the second output of NO 6 through DC2 15 and PF3 14 is connected to the first input of CM1 8, the output of CM1 8 through DC1 7 is connected to the second input of PFD 3, while the first output of UCH 9 is connected to the first input of CM2 12, the second output of UCH9 is connected to the input of TsVS 10, the output of TsVS 10 is connected through PF1 11 to the second input of CM2 12, and the output of CM2 12 is connected through PF2 13 to the second input CM1 8.

The frequency of the output oscillations of the hybrid multi-ring synthesizer, taken from the output of the coupler 6, is determined by the formula

F _mid = f _og N _dch2 N _dch3 [K ₁ f _cm1 / N _dch3 ± K _PLL1 R)], (1)

f _cm1 \u003d K ₁ (1 ± 1 / K _CWS ).

Here f _og is the frequency of the output oscillations of the GKOCH 1, N _dch2 is the division factor of the DF1 7, N _dch3 is the division factor of the DF2 15, K ₁ is the multiplication factor of the UCH 9, K _CVS is the ratio of the output frequency of the UCH 9 to the output frequency of the CVS 10, K _PLL1 - frequency multiplication factor PLL2 16, R - frequency division factor DC3 17.

The maximum and minimum values of the output frequency of the hybrid multi-ring synthesizer can be calculated by the formulas:

F _sch.max \u003d (F _chfd2.max + K ₁ (1 ± 1 / K _CVS ) / N _dch3 ) N _dch2 N _dch3 .

F _sch.min \u003d (f _{reference min} + K ₁ (1 ± 1 / K _CVS ) / N _dch3 ) N _dch2 N _dch3 . (2)

Here F _chfd2.max is the maximum allowable frequency of operation of the PFD 3, f _ref.min is the minimum frequency of the operation of the PFD 3, determined by the parameters of the LPF 4. The presence of terms (±1 / K _CVS ) in formulas (2) allows you to obtain a continuous series of values F _{s .max} and F _sch.min if you set the values of K _CVS >K ₁ /0.45.

Reducing the level of phase noise of the output oscillation of the hybrid multi-ring synthesizer is achieved through the operation of the DDS 10 in the first Nyquist zone. Indeed, consider a specific version of the hybrid multi-ring synthesizer, in which the 1508PL8T microcircuit is used as the CVS 10 and the following parameter values are set: f _og =120 MHz, K ₁ =7, K _CVS =21. In this case, the clock frequency of the DSC 10 will be f _T = f _og · N _dch2 = 840 MHz, the output frequency of the DSC 10 will be equal to f _CVS1 = f _T / K _DSC = 40 MHz. Let's take f _cm1 \u003d K ₁ (1-1 / K _CVS ) \u003d 800 MHz. The phase noise of the DDS 10 at frequency f _DDS is shown in FIG. 3, curve 1. If the DDS 10 operates in the second Nyquist zone, with an output frequency f _DDS2 = f _cm1 = 840 MHz, its phase noise will increase, as shown in FIG. 3, curve 2. Since the power of the phase noises introduced by the DDS 10 in the passband of the LPF 4 is recalculated to the output of the synthesizer in proportion to the square of the value of N _dch2 , the use of the proposed device, which has a lower level of phase noises of the DDS 10, really makes it possible to reduce the phase noise level at the output hybrid multi-ring synthesizer.

The operation of the CVS 10 in the first Nyquist zone makes it possible to reduce the level of side spectral components in the spectrum of the output oscillation. In FIG. Figure 4 shows the oscillation spectrum at the output of CM2 12 (Fig. 2) during the formation of the output oscillation of the DDS with a frequency of 168.5 MHz in the first Nyquist zone, with a clock (input) frequency of 840 MHz. The level of spurious spectral components is minus 76.862 dB and minus 79.089 dB relative to the level of the output waveform. Figure 5 shows the spectrum of fluctuations at the first input of the mixer 8 (figure 1) during the formation of the output oscillations of the TsVS 10 in the second Nyquist zone with a frequency of 671.5 MHz. The level of side spectral components is minus 69.645 dB and minus 75.92 dB relative to the level of the output waveform. Thus, the level of side spectral components is reduced by 3 - 6 dB.

An additional reduction in the level of phase noise and regular components in the output oscillation of the hybrid multi-ring synthesizer is achieved due to the filtering properties of the second phase-locked loop, and the elimination of the penetration of combination components that occur in SM1 8 and penetrate through NO 6 to the output of the hybrid multi-ring synthesizer, due to the use of PF3 14. tuned to the frequency of the output oscillation DCH2 15, which is k ₂ times (where k ₂ is the division factor of DCH2 15), less than the frequency of the output oscillation of the hybrid multi-ring synthesizer.

Claims (1)

Hybrid multi-ring frequency synthesizer containing a reference frequency oscillator, a frequency-phase detector, an annular low-pass filter, a voltage-controlled oscillator, a directional coupler, a frequency divider, a mixer, a frequency multiplier, a digital computational synthesizer and a bandpass filter, characterized in that additionally introduced a second mixer, a second bandpass filter, a third bandpass filter, a second frequency divider, a second phase-locked loop, and a third frequency divider, wherein the first output of the reference frequency generator is connected to the input of the second phase-locked loop, the second output of the reference frequency generator is connected to the input of the multiplier frequency, the frequency multiplier has two outputs, where the first output of the frequency multiplier is connected to the first input of the second mixer, the second output of the frequency multiplier is connected to the input of a digital computational synthesizer, the output of which is connected through the first bandpass filter to the second input of the second th mixer, the output of the second mixer through the second band-pass filter is connected to the second input of the first mixer, the output of which is connected through a frequency divider to the second input of the frequency-phase detector, the output of the second phase-locked loop through the third frequency divider is connected to the first input of the frequency-phase detector, the output of the frequency-phase detector through a series-connected low-pass ring filter and a voltage-controlled generator is connected to the input of the directional coupler, the second output of the directional coupler is connected to the first input of the first mixer through the second frequency divider and the third bandpass filter connected in series, the first output of the directional coupler is output of the proposed hybrid multi-ring synthesizer.

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