SU1046906A1 - Phase demodulator - Google Patents

Description

The invention relates to analog signal processing devices and may be used in resistometer technology, radar navigation and communications. A device for measuring angular modulation functions is known, comprising a series-connected limiter, a frequency discriminator and an integrator. When a frequency-modulated (FM) signal arrives with a deviation of DH, and a medium frequency to the limiter input, it is limited in amplitude and fed to the input of a frequency discriminator with a center frequency fp. Then the video signal taken from the output of the frequency discriminator whose amplitude the magnitude and the sign of the frequency deviation of the signal at the input of the frequency discriminator from the value of f are determined and input to the integrator. From the output of the integrator, the signal is taken, the envelope of which carries information about the angular modulation-9 (t) of the input signal. The frequency discriminator used in this device is executed according to a typical scheme. The most commonly used are frequency discriminators of the balanced type and frequency discriminators with frustrated circuits. A balanced type frequency discriminator contains two filters tuned to a medium frequency and having a weak inductive and strong capacitive coupling, a detecting circuit and a common load. The frequency discriminator with frustrated circuits contains two filters, the resonant frequencies of which are separated symmetrically with respect to the average frequency fp by the value of ± L. t, the detection circuit and the total load. As a result, when the frequency of the input signal deviates from fo, a voltage occurs at the output of the frequency discriminator, the sign and magnitude of which is determined by the direction and magnitude of the frequency deviation from TO. I Comparison of frequency discriminators shows that with the same slope of the characteristics, the frequency discriminator on frustrated circuits, all other conditions being equal, requires a filter with a slightly lower quality factor. Moreover, the filters used in frequency discriminators can be made from both elements with lumped parameters and from elements on surface acoustic waves (.)) A disadvantage of the known device for measuring the function of angular modulation is that it can only process frequency modulated (FM) signals. If a phase-modulated (FM) signal arrives at the input of this device, then at the moments of phase jumps, the first and second filters are affected by a wide range of frequencies, with the result that both filters are excited. Their impulse responses occur at different frequencies, but have the same envelopes, so after detecting these responses and their antiphase summing at the total load, the output signal of the frequency discriminator, and hence the entire device, is zero. Closest to the present invention is a phase demodulator comprising an input source with a limiter, the input of which is the input of a phase demodulator, serially connected first phase shifter, first multiplier and first bandpass filter, serially connected second multiplier and second bandpass filter; a reference signal shaping circuit, common to the first and second multipliers, made in the form of a series-connected reference signal generator, a third multiplier, whose signal input is the signal input of the reference signal shaping circuit, and a third band-pass filter, whose output is. This is the output of the reference signal generation circuit, which is connected to the inputs of the first and second multipliers through the second and third phasers, while the input of the first phase shifter and the signal inputs of the second multiplier and the reference signal generation circuit are connected to the outputs of the first and second band filters to the inputs of the adder. In the specified device, the input signal with a medium frequency tf is multiplied in the third multiplier with the signal of the reference frequency generator (si) ti and then passed through a filter tuned to a low difference frequency (i - Lf. This filter is a fundamental element, since sets the narrow band of the Lf of the entire device, which can be easily implemented, since the filtering is carried out at relatively low frequencies si (d). The rest of the scheme is intended to return to the center frequency% signal, while remaining in the received narrow band. To do this, use the compensation method to avoid the use of complex filtering circuits, which are necessary in this case, when a single-time mixing of the output signal of the narrow-band filter with the difference frequency W - i, and g mono frequency oscillations (I. In the compensation method, the difference frequency signal U | | - tf, allocated in a narrow DOP bandwidth by a bandpass filter, is transmitted to two channels, each of which contains an Tel, in one it is multiplied with a cosine oscillation frequency it. / resulting in the sum of two cosinusoids with difference and sum frequencies cos (a2) + cos (a - + In the other channel, the same difference frequency signal and / y) - UJ and the harmonic frequency oscillation using P / 2 phase shifters are converted into sinusoidal view, and then multiply with each other, and the product of two sinusoidal sin (ЦC - ifii) and .sin (UD) gives the difference cosine sine cos (- -cost, UJ) - (Yus +). Subtracting the signals of the first and second channels get rid of the difference frequency (u - tis) and leave the total w. i. Thus, the transition to the frequency of the input signal is realized, and the bandwidth of this signal is the same as that of the bandpass filter of a low center frequency i by a specified narrow band (Shf 2. The disadvantage of this device is the low demodulation accuracy demodulation frequency-modulated and phase-modulated signals. This goal is achieved by the fact that the phase demodulator containing the limiter, the input of which is the input of the phase demodulator, is serially connected The first phase shifter, the first multiplier and the first band-pass filter, the second multiplier and the second band-pass filter are connected in series, the reference signal shaping circuit common to the first and second multipliers and made in the form of a series-connected reference signal generator, the third multiplier whose signal input is the signal input of the reference signal shaping circuit and the third bandpass filter, the output of which is the output of the reference signal shaping circuit, as well as the second The transformer and adder, whose output is the output of a phase demodulator, between the output of the limiter and the input of the first phase shifter a weight filter is inserted, between the output of the first bandpass filter and the first input of the adder and between the output of the second bandpass filter and the input of the phase rotator, respectively, the first 1G of the second integrator and also introduced a fourth band-pass filter, the input of which is connected to the output of the limiter, and the output to the signal inputs of the second multiplier and the reference signal forming circuit, with This output of the second phase shifter is connected to the second input of the adder, and the output of the reference signal shaping circuit is connected to the reference inputs of the first and second multipliers directly, Figure 1 shows the block diagram of the proposed device; FIG. 2, plots, see its operation. The phase demodulator contains a limiter 1, the input of which is the input of a phase demodulator, successively connected the first phase shifter 2, the first multiplier 3, the first band-pass filter 4, sequentially connected the second multiplier 5 and the second band-pass filter 6, the reference signal generating circuit 7, comprising the reference signal generator 8, the third multiplier 9, and the third band-pass filter 10, the second phase shifter 11, the adder 12, the weight filter 13, the first and second integrators 14 and 15, four rty bandpass filter 16, The apparatus operates as follows. When a FM signal arrives at its input in the form of a sequence of four elementary radio pulses of duration ty, each of different amplitudes with a frequency of filling Wf, and phase jumps on T between them. After the limiter 1, the FM signal of a constant amplitude Ad is fed to the inputs of the weight filter 13 and the fourth band filter 1B, which has a transmission bandwidth Dc with an average frequency of the OC, and is delayed by a signal. the magnitude of ρp, the type of signal at the output of limiter 1 is given in Fig. 2a; This signal can be written in general form XiU) -AoC05tu; o-t- -® -t) i-4o, U) where tfj is the initial phase; eit) is the function of angular modulation, which, within one modulation period, takes the value O, P. The combination of the weight filter 13 with the first phase shifter 2 at T / ij) 6- gives a total amplitude-frequency characteristic 1AChC) linearly increasing in the direction of the upper frequency of the passband and the linear phase-frequency characteristic (FFH) shifted by tf / relative to the origin. Thus, at the output of the first phase rotation of the body 2, the signal has the form (iU) -Ao Cli; o + fc (-t) sinLuJoi - & t 3 (2) and is an oscillation frequency U with a complex envelope proportional to the instantaneous angular frequency (Fig. 2b). From FIG. 26 it is visible / that this signal has gaps at the moments of jumps. Phase on P. Such a signal arrives at the first input of the first multiplier 3. The limited FM signal from the output of limiter 1 is fed to the input V of the fourth band-pass filter 16 with a bandwidth L tsj average frequency tiJo with delayed signal t. The fourth vacuum filter 16 has a rectangular frequency response and a linear phase response and is intended to limit the width of the spectrum of the signal from the output of limiter 1 in the frequency band i, since it is known that its frequency spectrum is enlarged when the signal is limited. The FM signal X-l6 (:) tAoCOS: U)) from the output of the fourth band-pass filter 16 is fed to the inputs of the second. th and third multipliers 5 and 9. The second input of multiplier 9 receives harmonic oscillation h, frequency (L from generator 8. At the output of multiplier 9, a FM signal of the difference frequency ttb - -f is extracted from the output of multiplier 9, namely i oW AoCosC (u; o-№i) -kf-9t t-Vi 3.1 G where Lf (for tf g - g the initial phase of the generator 8, which is fed to the second inputs of the multipliers 3 and 5. At the output of the multiplier 3 by a band-pass filter 4 signal is highlighted)) - AitWo + eC-t) iyiLmii-4rb -A, tUJote4-t) 35ivi (.ui t Vr4K) (5), formed by the difference of the frequencies - iV of oscillations arriving at the inputs ne multiplier 3. This signal is a sequence of four elementary radio pulses of constant amplitude frequency and / and, and the gaps of the current phase between the radio pulses are preserved, but all radio pulses have the same initial phases. It enters the input of the first integrator 14, which is a filter with a medium frequency (V., frequency response equal to the modulus of the function (sin x) / x, and a pulse with the NOY characteristic in the form of a radio pulse with a rectangular envelope of frequency w. And duration T the duration of the elementary pulse in the input FM signal, but not less than the duration of the entire input signal.The response of the integrator 14 to each elementary radio pulse of constant amplitude A with duration ty, and frequency tf of the input signal is a convolution A pulse with the impulse response of the integrator 14. Thus, from each elementary radio pulse of the input signal at the output of the integrator 14, a radio pulse is received with a filling frequency q t of duration U +, the envelope of which increases linearly over the time interval tyj, is constant for the time interval T and linearly decreases time interval with a duration t. These responses of the integrator 14 to each element of the starting pulse are delayed relative to each other by the value of ty, as well as the elementary radio pulse in the input signal of The integrator 14, and summed it in phase, since the initial phases of all elementary radio pulses are equal. Therefore, the signal at the output of the integrator 14 (Fig. 2c) is a radio pulse of the form) -A-, U) S "ai-rg -itT (;) f6) of duration, where T is the duration of the impulse response of the integrator 14 / tp, FM duration signal. At tg, t, i.e. 2T, the envelope A. (t) of this signal is proportional to the current as 4j (-t) (- t) (7) of the input signal in the time interval from the beginning of the integrator response 11 to T, and in its second half from T to 2T i A (t) is proportional to the mirrored current phase. This signal is fed to the first input of the adder 12. To the second input of the adder 12 an integrated and phase-shifted signal is fed by 7G / 2, which is formed: at the output of multiplier 5. To the first input of multiplier 5 from the output of bandpass filter 16, a FM signal is received with a duration tg, , representing a sequence of four radio pulses of the same amplitude with a medium frequency (Ap and with phase jumps on the TG between them. The second input of the multiplier 5 receives a FM signal from the output of the bandpass filter 10, which differs from At the first input, only the average filling frequency of 0 - ft-fN is output. At the output of multiplier 5, the signals of the total

and differential frequency. The difference frequency signal uip - at - u w is a bandpass filter 6 and is a radio pulse with a constant amplitude, a duration of the filling frequency. 2d), i.e. SHOCK) (OU4 -t-iPr). (8) This signal is input.

the second integrator 15, whose characteristics are the same as that of the first integrator 14. The output signal of the integrator 15 (Fig. 2e) is a radio pulse) Aji.C) cos (oij-t) (9) with a duration of 1: T + tpJ. When tftx t, i.e. tgjj, y 2Т, the envelope of this signal has a triangular form in the time interval from the beginning of the integrator response 15 to T and is proportional to the linear phase term of the input FM signal, and in the second half

 from T to 2T is proportional to the mirror-phase | phase term

To obtain the output modulator Q (t) of the input FM signal at the output of adder 12, it is necessary to eliminate the linear phase term t in the output signal of the first integrator 14 for this signal, subtract the input signal of the second integrator 15 from this signal. Therefore, before summing the output signal of the integrator 14 enters the phase shifter 11 on the vehicle /. Insofar as

this signal is narrowband then shift

Phase / a is equivalent to introducing an additional delay to this signal such that the phase increment is equal to the frequency. In this case, the signal at the output of the phase shifter 11 has the form 1 D: LgSho5 (.) - AaWsinCu / H-ifrK () In addition, it is necessary that the amplitudes of the signals at the inputs of the integrators 14 and 15 are equal.

Thus, two oscillations are applied to the adder 12, differing in phase by the value of T x ds-cb LD4) sin (cm-bcx ttt) () sin (i -t-jlv) c) The signal on the adder's respiration signal looks like ( Fig. 2e). -. .

Xn (O - CA-Ittl-AaU) (lUi-l- r tTf) The envelope of this signal is equal to A (t) -) proportional to the angular modulation function 9 (t) of the input FM signal at the time interval from the start of the adder 12 response to T, in the second half of it from T to 2T, the envelope A (t) -,) is proportional to the mirror function of the angular modulation.

The proposed phase demodulator makes it possible to unambiguously determine the function of the angular modulation of the frequency modulated and phase modulated signals, which expands the functionality of the processing devices in which it is used and improves the accuracy.

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Claims (1)

PHASE DEMODULATOR containing a limiter whose input is an input; phase demodulator, the first phase shifter connected in series, the first multiplier and the first bandpass filter, the second multiplier and the second bandpass filter connected in series, the reference signal generation circuit common to the first and second multipliers and made in the form of a series-connected generator. the reference signal, the third multiplier, the signal input of which is the signal input of the reference signal generation circuit, and the third bandpass filter, the output of which is the output of the reference signal generation circuit, as well as the second phase shifter and adder, the output of which is the output of the phase demodulator, In order to increase the accuracy of demodulation of the frequency-modulated and phase-modulated signals, a weight filter is introduced between the output of the limiter and the input of the first phase shifter, between the output of the first bandpass filter and the first input of the adder and between the output of the second bandpass filter and the input of the second phase shifter, the first and second integrators are respectively introduced, and the fourth bandpass filter is also introduced, the input of which is connected to the output of the limiter, and the output to signal inputs the second multiplier and the reference signal generation circuit, wherein the output of the second phase shifter is connected to the second input of the adder, and the output of the reference signal generation circuit is connected to the reference inputs of the first and second alternator ozhiteley directly. SU „, 1046906