RU2480907C1 - Receiver of signals of satellite and radio-navigation glonass and navstar systems - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: receiver of signals of satellite radio-navigation systems GLONASS and Navstar comprises an antenna, an input feeder 1, a wideband filter-preselector 2, the first 3 and second 5 low-noise amplifiers, the first 4, second 9 and third 14 band filters, the first 6 and second 13 mixers, a frequency synthesiser 7, a reference thermostatted generator 8, the first 10 and second 15 amplifiers of intermediate frequency, a unit 11 of complex conversion of a signal, a unit 12 of automatic regulation of amplification, the first 17 and second 24 threshold units, a correlator 16, the first 18 and second 26 keys, a selector 19 of phase-shift keyed signals, the first 20 and second 22 spectrum analysers, a phase doubler 21, a unit 23 of comparison, a delay line 25, the first 27 and second 29 narrow-band filters, a multiplier 28 and a phase detector 30.

EFFECT: improved selectivity and noise immunity of a receiver by selection of phase-manipulated signals and provision of symmetry of frequencies ω_r1 and ω_r2 of a frequency synthesiser relative to bearing frequency ω_C of received phase-manipulated signals.

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Description

The proposed receiver relates to satellite radio navigation and can be used on moving objects, for example, to control the movement of ships, both surface and air in difficult weather conditions, for the primary processing of information received from two mutually synchronized satellite radio navigation systems GLONASS and Navstar.

Known receivers of signals from satellite radio navigation systems (ed. Certificate of the USSR No. 1.246.402, RF patents No. 2.110.140, 2.118.046, 2.231.218; US patents No. 588.246, 5.991.612; EP patent No. 0,035. 050; Abrosimov V.I. et al. Use of the Navstar system for determining the angular orientation of objects. - Foreign Radio Electronics, 1989, No. 1, p. 49; Networked Satellite Radio Navigation Systems. Edited by BC Shebshaevich. - M., 1993; Mishchenko I.N., Romanov L.M. New Developments of Satellite Radio Navigation Systems. — Foreign Radio Electronics, 1989, No. 1, p. 68-82; Enedzava S., Tanaka N. Communication on Microwave. - ., 1991, ed. Communication, s.146-173 and others).

Of the known receivers, the closest to the proposed one is the “Navstar and GLONASS Satellite Radio Navigation Systems Signal Receiver” (RF patent No. 2.231.218, H04B, 1/06, 2002), which is chosen as a prototype.

The specified receiver contains an antenna, an input feeder, a broadband filter preselector, a first low-noise amplifier, a first band-pass filter, a second low-noise amplifier, a first mixer, a frequency synthesizer, a reference thermostatically controlled oscillator, a second band-pass filter, a first and second intermediate frequency amplifiers, an integrated frequency conversion unit , an automatic adjustment unit, a second mixer, a third band-pass filter, a correlator, a threshold unit and a key. The receiver provides suppression of false signals (interference) received on the mirror and Raman channels. This is achieved by the fact that the voltage of the frequency synthesizer is spaced twice the value of the intermediate frequency

ω _G2 -ω _G1 = 2ω _PR

and are chosen symmetric with respect to the frequency ω _{C of the} main channel

ω _C -ω _G1 = ω _G2 -ω _C = ω _PR .

This circumstance leads to a doubling of the number of additional receiving channels (figure 2), but creates favorable conditions for their suppression using the correlation processing of the received signals.

However, due to various destabilizing factors, including the Doppler effect, the carrier frequency ω _{C of the} received signals with phase shift keying (QPSK) changes and the symmetry of the frequencies ω _G1 and ω _{G2 of} the frequency synthesizer relative to the carrier frequency ω _{C of the} received QPSK signals is violated, which reduces the selectivity and noise immunity of the receiver.

In addition, at the input of the receiver, along with useful QPSK signals, interference and other signals are received, which also reduces the selectivity and noise immunity of the receiver.

An object of the invention is to increase the selectivity and noise immunity of the receiver by selecting phase-shifted signals and ensuring the symmetry of the frequencies ω _G1 and ω _{G2 of} the frequency synthesizer relative to the carrier frequency ω _{C of the} received phase-shifted signals.

The problem is solved in that the signal receiver of satellite navigation systems containing, in accordance with the closest analogue, a series-connected antenna, an input feeder, a broadband filter preselector, a first low-noise amplifier, a first band-pass filter and a second low-noise amplifier, a series-connected first mixer, a second input which through a frequency synthesizer is connected to the output of the reference thermostatically controlled oscillator, a second bandpass filter, a first intermediate frequency amplifier, first the first key and the complex signal conversion unit, the second and third inputs of which are connected to the second and third outputs of the frequency synthesizer, respectively, the second mixer in series, the second input of which is connected to the fourth output of the frequency synthesizer, a third bandpass filter, a second intermediate frequency amplifier, a correlator, a second the input of which is connected to the output of the first intermediate frequency amplifier, and the first threshold block, the output of which is connected to the second input of the first key, the output of which is through the auto block The gain control is connected to the second inputs of the first and second low-noise amplifiers, the first and second intermediate frequency amplifiers, differs from the closest analogue in that it is equipped with two spectrum analyzers, a phase doubler, two narrow-band filters, a comparison unit, a second threshold block, a delay line, a second key, a multiplier and a phase detector, and a phase doubler, a second spectrum analyzer, a comparison unit, a second input to the output of the second low-noise amplifier are connected in series of which, through the first spectrum analyzer, is connected to the output of the second low-noise amplifier, the second threshold block, the second input of which is connected to its output through the delay line, and the second key, the second input of which is connected to the output of the second low-noise amplifier, and the output is connected to the first inputs of the first and second mixers, the first narrow-band filter and a phase detector, the output of which is connected to the second input of the frequency synthesizer, to the first output of the frequency synthesizer, to the first output are connected to the output of the phase doubler frequency synthesizer connected in series multiplier, a second input coupled to a fourth output of the frequency synthesizer, and a second narrow band filter, whose output is connected to a second input of the phase detector.

The structural diagram of the proposed receiver is presented in figure 1. A frequency diagram explaining the principle of formation of additional reception channels is shown in FIG.

The receiver of the GLONASS and Navstar satellite radio navigation systems contains a series-connected antenna, an input feeder 1, a broadband filter preselector 2, a first low-noise amplifier 3, a first band-pass filter 4, a second low-noise amplifier 5, a phase doubler 21, a second spectrum analyzer 22, a comparison unit 23 the second input of which, through the first spectrum analyzer 20, is connected to the output of the second low-noise amplifier 5, the second threshold block 20, the second input of which is connected through its delay line 25 to its output, the second key 26, Ora input coupled to an output of the second low-noise amplifier 5, a first mixer 6, a second input coupled to the first output of the frequency synthesizer 7, a second bandpass filter 9, the first intermediate frequency amplifier 10, first switch 18 and unit 11 a complex signal conversion. A second mixer 13, the second input of which is connected to the fourth output of the frequency synthesizer 7, the third band-pass filter 14, the second intermediate-frequency amplifier 15, the correlator 16, the second input of which is connected to the output of the first intermediate-frequency amplifier 10, and the first threshold unit 17, the output of which is connected to the second input of the first key 18. The second inputs of the first low-noise amplifier 3, the second low-noise amplifier 5, the first 10 and second 15 amplifiers of intermediate frequency through the 12 av block the gain gain control is connected to the output of the first key 18. The second and third inputs of the complex signal conversion unit 11 are connected to the second and third output of the frequency synthesizer 7. The output of the phase doubler 21 is connected in series with the first narrow-band filter 27 and the phase detector 30, the output of which is connected to the second input of the frequency synthesizer 7, the first input of which is connected to a reference thermostated generator 8. The multiplier 28, the second input of which is connected in series to the first output of the frequency synthesizer 7 connected to the fourth output of the frequency synthesizer 7, and a second narrow-band filter 29, the output of which is connected to the second input of the phase detector 30.

Spectrum analyzers 20 and 22, a phase doubler 21, a comparison unit 23, a second threshold unit 24, a delay line 25, and a second key 26 form a selector 19 of the PSK signals.

The proposed receiver operates as follows.

At the antenna input of the receiver, signals from the spacecraft of two satellite radio navigation systems GLONASS and Navstar S _L are received simultaneously, which in the two received frequency bands L ₁ and L ₂ have the form:

S _j L ₁ (t) = P _j (t) D _j (t) cos (ω _j L ₁ t + φ _j L ₁ ),

S _j L ₂ (t) = P _j (t) D _j (t) cos (ω _j L ₂ t + φ _j L ₂ ),

where P _j (t) is the pseudo-random envelope of the j-th HKA, j = 1, 2, ..., n;

D _j (t) - navigation message of the j-th KA;

_ωj L ₁ , ω _j L ₂ - carrier frequencies in the ranges L ₁ and L ₂ from the j-th HKA;

φ _j L ₁ , φ _j L ₂ - the initial phase of the received signals.

The frequency response of the receive path is determined by the frequency spectrum of the received signals. The signal spectrum of navigational spacecraft (HKA) of the Navstar system when working with the C / A code is (1574.42-1594.24) MHz, the signal spectrum of the HKA of the GLONASS system with C / A code is (1602-1620) MHz .

This means that the total frequency band of the received signals is

1574.42≤Δω≤1620 MHz,

that is, the occupied frequency band Δω is 50 MHz.

Received QPSK signals from the antenna enter the input feeder 1, which is a quarter-wave segment of the coaxial line closed on one side and serves to coordinate the parameters of the antenna and the input circuits of the receiver. From the output of the feeder 1, the QPSK signals go to the input of the broadband filter preselector 2, which serves to limit the frequency band of the received signals in the range of 1574.42-1621 MHz. The specified filter, made on microwave lines, implements a 5th order elliptical Cower bandpass filter. Broadband filter preselector 2 has an important advantage, namely, an almost linear phase characteristic in the passband of the filter, which is a great advantage when working with complex phase-shift keyed signals transmitted from satellites. This leads, for example, to the fact that the filter preselector 2 has the same linear group delay time τ in the passband equal to about 2.5 ns. Such an implementation leads to the fact that there is no need to use a special calibrator to ensure the same group delay time τ for all signals received from the satellite.

From the output of the preselector filter 2, the signal is fed to the input of a low-noise amplifier 3, the output of which is connected to the input of a band-pass filter 4, the output signal of which is fed to the input of the second low-noise amplifier 5.

The bandpass filter 4 is designed to eliminate additional ripple in the obstacle strip of the broadband filter-preselector 2, as well as for isolation between low-noise amplifiers 3 and 5.

The main amplification of the receiving path is provided by low-noise amplifiers 3 and 5, which are made on the basis of gallium arsenide transistors with a Schottky barrier. The parameters of low-noise amplifiers 3 and 5 are as follows: a gain of 35 dB; the range of received frequencies is 1-8 GHz with uneven amplitude-frequency characteristics of 1 dB and a noise figure of 1.1 dB.

Received QPSK signal

u _C (t) = U _C cos [ω _C t + φ _k (t) + φ _C ], 0≤t≤T _C ,

where φ _K (t) = {0, π} - manipulated phase component forming the law of PSK in accordance with the modulating code M (t), wherein φ _k (t) = const at kτ _E <t <(k + 1) τ _E and can change abruptly at t = kτ _E , i.e. at the borders between elementary premises (k = 1, 2, ..., N-1);

τ _E , N - the duration and number of chips that make up a signal of duration T _C (T _C = 1 / τ _E ), (N = 1023),

from the output of the second low-noise amplifier 5 is supplied to the inputs of the first spectrum analyzer 20 and phase doubler 21. The output of the latter produces a harmonic voltage

u ₁ (t) = U ₁ cos (2ω _C t + 2φ _C ), 0≤t≤T _C ,

.Where

.

Since 2φ _k (t) = {0.2π}, phase manipulation is already absent in the indicated voltage.

The width of the spectrum Δf ₂ , the second harmonic of the signal is determined by the duration T _{C of the} signal

Whereas the spectrum width Δf _{C of the} QPSK signal is determined by the duration of its elementary premises

,

,

those. spectrum width Δf _{C of the} second harmonic of the spectrum is N times smaller than the spectrum width of the input signal

Δf _C / Δf ₂ = N.

Therefore, when the phase of the QPSK signal is multiplied by two, its spectrum collapses N times. This circumstance makes it possible to detect and select the QPSK signal even when its power at the receiver input is less than the power of noise and interference.

The width of the spectrum Δf _{C of the} input QPSK signal is measured using the spectrum analyzer 20, and the spectrum width Δf ₂ , the second harmonic of the signal is measured using the spectrum analyzer 22.

Voltages U _I and U _II proportional to Δf _C and Δf _2, respectively, from the outputs of the analyzers 20 and 22 of the spectra are fed to two inputs of the comparison unit 23. Since U _I >> U _II , a positive voltage is generated at the output of the comparison unit 23, which exceeds the threshold level U _por1 in the threshold block 24. The threshold level U _por1 is chosen so that it does not exceed random interference. When the threshold level U _pore1 is exceeded, a constant voltage is generated in the threshold block 24, which is supplied to the input of the delay line 25 and to the control input of the key 26, opening it. In the initial state, the thorn 26 is always closed. In this case, the received PSK signal u _C (t) from the output of the second low-noise amplifier 5 through the public key 26 is supplied to the first inputs of the mixers 6 and 13, the second inputs of which are supplied with voltage from the first and fourth outputs of the frequency synthesizer 7:

u _Г1 (t) = U _Г1 cos (ω _Г1 t + φ _Г1 ),

u _Г2 (t) = U _Г2 cos (ω _Г2 t + φ _Г2 ).

Moreover, the frequencies of these voltages are spaced by a double value of the intermediate frequency

ω _Г2 -ω _Г1 = 2ω _пр

and are chosen symmetric with respect to the frequency ω _{C of the} main channel

ω _C -ω _{r1 r2} = ω = ω _C -ω _pr.

This circumstance leads to a doubling of the number of additional receiving channels (figure 2), but creates favorable conditions for their suppression using the correlation processing of the received signals.

At the output of the mixers 6 and 13, voltages of combination frequencies are generated. Amplifiers 10 and 15 are allocated voltage intermediate frequency

u _CR1 (t) = U _CR1 cos [ω _CR1 t + φ _k (t) + φ _CR1 ],

u _CR2 (t) = U _CR2 cos [ω _CR2 t + φ _k (t) + φ _CR2 ], 0≤t≤T _C ;

;

;

Where

;

;

ω _CR = ω _C- ω _G1 = ω _G2 -ω _C is the intermediate frequency;

φ _pr1 = φ _C -φ _G1 ; φ _pr2 = φ _Г2 -φ _С.

The _voltages u _CR1 (t) and u _CR2 (t) from the outputs of the amplifiers 10 and 15 of the intermediate frequency are supplied to the two inputs of the correlator 16, at the output of which a correlation function R (τ) is formed. The latter is compared with the threshold level U _por2 in the threshold block 17. The threshold voltage U _{por2 is} exceeded only at the maximum value of the correlation function R _max (τ).

Since the voltage u _CR1 (t) and u _CR2 (t) from the outputs of the amplifiers 10 and 15 of the intermediate frequency are formed by the same QPSK signal received on the main channel at a frequency ω _C (Fig. 2), then between these voltages strong correlation, the correlation function reaches its maximum value R _max (τ), which exceeds the threshold level U _pore2 . It should be noted that the correlation function of the QPSK signals has a remarkable property: a high level of the main lobe and a low level of side lobes. When the threshold level U _p2 is exceeded, a constant voltage is generated in the threshold block 17, which is supplied to the control input of the key 18 and opens it. In the initial state, the key 18 is always closed.

In this case, the output voltage u _pr1 (t) of the intermediate frequency amplifier 10 is supplied through the public key 18 to the input of the automatic gain control unit 12 and to the information input of the complex signal conversion unit 11, in which quadrature processing of input information is implemented by supplying control inputs to this node rectangular pulses with a shift by a quarter of the period, while the outputs J ₁ and J ₂ form a sine, and at the outputs Q ₁ and Q ₂ - the cosine components of the output information signal.

To ensure a constant gain within specified limits, an automatic gain control unit 12 is used, covering low-noise amplifiers 3 and 5, and amplifiers 10 and 15 of intermediate frequency.

To ensure the symmetry of the carrier frequency ω _{C of the} received FMN signals with respect to the frequencies ω _G1 and ω _{G2 of the} frequency synchronizer 7, a phase-locked loop is used, consisting of a phase doubler 21, a first narrow-band filter 27, and a phase detector 30 connected to the output of the second low-noise amplifier 5 the second input of which through series-connected multiplier 28 and the second narrow-band filter 29 is connected to the first and fourth outputs of the frequency synchronizer 7, and the output is connected to the second input synthesizer 7 frequencies. The harmonic voltage u ₁ (t) from the output of the phase doubler 21 is extracted by the first narrow-band filter 27 and is supplied to the first input of the phase detector 30.

Voltages u _Г1 (t) and u _Г2 (t) from the first and fourth outputs of the frequency synthesizer 7 are supplied to two inputs of the multiplier 28, at the output of which a harmonic voltage is generated

u _Г (t) = U _Г cos (ω _Г t + φ _Г ),

;Where

;

ω _Г = ω _Г2 -ω _Г1 = 2ω _пр ,

φ _G = φ _G2 -φ _G1 ,

which is allocated by the second narrow-band filter 29 and fed to the second input of the phase detector 30.

If these voltages differ from each other in frequency or phase, then a control voltage is generated at the output of the phase detector 30. Moreover, the amplitude and polarity of this voltage depends on the degree and direction of deviation of the carrier frequency ω _{C of the} received FMN signal relative to the frequencies ω _G1 and ω _{G2 of the} frequency synthesizer 7. The control voltage acts on the control (second) input of the frequency synthesizer 7, changing the frequencies ω _G1 and ω _G2 so that the carrier frequency ω _{C of the} received FMN signal remains symmetric with respect to the frequencies ω _G1 and ω _{G2 of the} synthesizer 7 frequencies ω _C- ω _G1 = ω _Г2- ω _С = ω _ol , ω _Г2 -ω _Г1 = 2ω _av

The delay time τ _{3 of} the delay line 25 is selected so that it is possible to detect, select, fix and convert the received PSK signal. After this time, the voltage from the output of the threshold unit 24 through the delay line 25 is supplied to the control input of the threshold unit 24 and resets its contents to zero. Since that time, the selector 19 QPSK signals is ready to receive the next QPSK signal from the navigation satellites of the GLONASS and Navstar systems.

The operation of the receiver described above corresponds to the case of receiving FMN signals on the main channel at a frequency ω _C (Fig. 2).

If a complex signal (interference) is received through the first mirror channel at a frequency of ω ₃₁ , then the output of the mixers 6 and 13 produces voltages of the following frequencies:

ω ₁₁ = ω _Г1 -ω ₃₁ = ω _ol ,

ω ₁₂ = ω _Г2 -ω ₃₁ = 3ω _pr

where the first index denotes the channel number on which a false signal is received (interference);

- the second index denotes the frequency of the synthesizer 7 frequencies involved in the conversion of the frequency of the false signal (interference).

However, only voltage with a frequency of ω ₁₁ falls into the passband of an intermediate frequency amplifier 10. The output voltage of the correlator 16 in this case is zero, the key 18 does not open and a false signal (interference) received through the first mirror channel at a frequency of ω ₃₁ is suppressed.

If a false signal (interference) is received through the second mirror channel at a frequency of ω ₃₂ , then the outputs of the mixers 6 and 13 generate voltages of the following frequencies:

ω ₂₂ = ω ₃₂ -ω _Г2 = ω _ol ,

₂₁ ω ₃₂ = ω -ω _G1 = 3ω _pr.

However, only voltage with a frequency of ω ₂₂ falls into the passband of the intermediate frequency amplifier 15. The output voltage of the correlator 16 is also equal to zero, the key 18 does not open, and a false signal (interference) received via the second mirror channel at a frequency of ω ₃₂ is suppressed.

For a similar reason, other false signals (interference) received on the first Raman channel at a frequency ω _k1 , or on a second Raman channel at a frequency ω _k2 , or any other Raman channel, are also suppressed.

If false signals (interference) are simultaneously received, for example, through the first and second mirror channels at frequencies ω ₃₁ and ω ₃₂ , then the outputs of the mixers 6 and 13 generate voltages of the following frequencies:

ω ₁₁ = ω _Г1 -ω ₃₁ = ω _ol ,

ω ₁₂ = ω _Г2 -ω ₃₁ = 3ω _pr

ω ₂₂ = ω ₃₂ -ω _Г2 = ω _ol ,

₂₁ ω ₃₂ = ω -ω _G1 = 3ω _pr.

In this case, voltages with frequencies ω ₁₁ and ω ₂₂ fall into the passband of amplifiers 10 and 15 of intermediate frequency, respectively. However, the key 18 in this case also does not open. This is because the false signals (interference) are received at different frequencies ω ₃₁ and ω ₃₂ and there is a weak correlation between them. The correlation function R (τ) does not reach the maximum value and does not exceed the threshold level U _pore2 in the threshold block 17, the key 18 does not open, and false signals (interference) received simultaneously through the first and second mirror channels at the frequencies ω ₃₁ and ω ₃₂ are suppressed .

For a similar reason, false signals (interference) received simultaneously on two or more other channels are also suppressed.

The following advantages have been achieved in the receiver:

a) providing the ability to receive and process signals from two satellite radio navigation systems GLONASS and Navstar using one receiving path, which means that a significant simplification of the receiving equipment has been achieved;

b) the implementation of the receiver can be carried out using one conversion to an intermediate frequency in two channels with the aim of further digital processing of signals received from the spacecraft of satellite radio navigation systems, and thereby ensures high reliability and accuracy of the circuit;

c) the receiver provides higher accuracy of reproducing input information through the use of filters with elliptic approximation, which implements a linear phase-frequency characteristic and, as a result, the same and minimum group delay time for all received signals;

e) the receiver provides increased selectivity and noise immunity of receiving signals from the GLONASS and Navstar satellite radio navigation systems by suppressing false signals (interference) received via mirror and Raman channels. This is achieved due to the correlation processing of the received signals and the use of the remarkable property of the correlation function of the FMN signals, which has a very high level of the main lobe and a low level of side lobes.

Thus, the proposed receiver in comparison with the prototype and other technical solutions for a similar purpose provides increased selectivity and noise immunity of receiving signals from satellite radio navigation systems GLONASS and Navstar. This is achieved through the detection and selection of QPSK signals among noise, interference, and other signals, as well as ensuring the symmetry of the frequencies ω _G1 and ω _{G2 of} the frequency synthesizer relative to the carrier frequency ω _{C of the} received QPSK signals, which is disturbed due to various destabilizing factors, and including the Doppler effect. In this case, the detection and selection of QPSK signals are based on convolution of the spectrum of these signals due to the doubling of their phase. And the symmetry of the carrier frequency ω _{С of the} received FMN signals with respect to the frequencies ω _Г1 , and ω _{Г2 of} the frequency synthesizer is achieved using the automatic frequency adjustment system.

Claims (1)

A signal receiver of satellite radio navigation systems, comprising a series-connected antenna, an input feeder, a broadband filter preselector, a first low-noise amplifier, a first band-pass filter and a second low-noise amplifier, a series-connected first mixer, the second input of which is connected through the frequency synthesizer to the output of the reference thermostated generator, and a band-pass filter, a first intermediate frequency amplifier, a first key and a complex signal conversion unit, second and third inputs to of which are connected to the second and third outputs of the frequency synthesizer, respectively, in series with a second mixer, the second input of which is connected to the fourth output of the frequency synthesizer, a third bandpass filter, a second intermediate frequency amplifier, a correlator, the second input of which is connected to the output of the first intermediate frequency amplifier, and the first threshold unit, the output of which is connected to the second input of the first channel, the output of which through the automatic gain control unit is connected to the second inputs of the first and second low-noise amplifiers, the first and second intermediate frequency amplifiers, characterized in that it is equipped with two spectrum analyzers, a phase doubler, two narrow-band filters, a comparison unit, a second threshold block, a delay line, a second key, a multiplier and a phase detector, and to the output of the second a low-noise amplifier, a phase doubler, a second spectrum analyzer, a comparison unit, the second input of which is connected through the first spectrum analyzer to the output of the second low-noise amplifier, are connected in series there is a threshold unit, the second input of which is connected to its output through the delay line, and the second key, the second input of which is connected to the output of the second low-noise amplifier, and the output is connected to the first inputs of the first and second mixers, the first narrow-band filter is connected in series to the output of the phase doubler and a phase detector, the output of which is connected to the second input of the frequency synthesizer, a multiplier is connected to the first output of the frequency synthesizer, the second input of which is connected to the fourth output of the synthesizer the one and second narrowband filter whose output is coupled to a second input of the phase detector.

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