JPS6347183B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a baseband type carrier wave recovery circuit.

Various configurations of carrier wave regeneration circuits that regenerate carrier waves for demodulating received PSK modulated waves are already known. For example, a 4-phase PSK modulated wave is multiplied by 4 to become an unmodulated signal, and then frequency-divided by 4 to reproduce a carrier wave that is phase-synchronized with the received signal. A modulation method, a baseband processing method using the output of a Costas loop, etc. are known.

Since the baseband processing method does not directly reproduce the carrier wave from the received PSK modulated wave,
Usually, a phase locked circuit using a voltage controlled oscillator is provided. For example, as shown in FIG. 1, a phase locking circuit is configured by a phase detector 1, a baseband processing circuit 2, an amplifier 3, a low-frequency amplifier 4, and a voltage-controlled oscillator 5, and the output of the voltage-controlled oscillator 5 is converted into a regenerated carrier. That is.

However, in the conventional baseband carrier regeneration circuit shown in Fig. 1, widening the pull-in range causes the problem of false pull-in, and in order to prevent this false pull-in, a high-stability voltage-controlled crystal oscillator is used. It is proposed to use However, voltage controlled crystal oscillators are expensive and have the disadvantage of having a narrow pull-in range.

Therefore, in order to widen the pull-in range, a sweep circuit 10 and a high stability oscillator 6 such as a crystal oscillator are provided as shown in FIG. The output is added to a mixing circuit 7, a frequency difference component is extracted, this frequency difference component is counted by a counter 8, and when the frequency difference is larger than a predetermined value, a determination circuit 9
starts the sweep circuit 10, adds the outputs of the sweep circuit 10 using the summation circuit 11 to obtain a control voltage for the voltage controlled oscillator 5, and sweeps the oscillation frequency. Therefore, in the pseudo-retraction state, a sweep operation is performed due to the large frequency difference, and the retraction operation is performed after escaping from the pseudo-retraction state.

However, even if you escape from the pseudo-pull-in state, you may be pulled into another pseudo-pull-in point by the sweep signal, so in order to expand the pull-in range, carefully set the sweep frequency, sweep signal, etc. However, it has the drawback that it is not easy to set, manufacture, and adjust.

SUMMARY OF THE INVENTION An object of the present invention is to provide a carrier wave regeneration circuit which can eliminate the above-mentioned drawbacks, expand the pull-in range, and prevent false pull-in.

In order to achieve the above object, the present invention makes it possible to easily obtain a frequency difference component between a reproduced carrier wave in a baseband processing method and a received modulated wave of an input signal, extracts this frequency difference component, and extracts the frequency difference component. A discriminating circuit determines whether the output is away from the pseudo pull-in frequency or not, and an isolated pulse of the output of the differentiating circuit is added as a control signal so that the oscillation frequency of the voltage controlled oscillator is directed toward the input signal frequency.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram of an embodiment of the present invention;
FIG. 4 is a time chart of waveforms in the case of FIG. 3, where A and D are the output waveforms of the low frequency converter 30, B and E are the output waveforms of the discrimination circuit 36, and C and F are the output waveforms of the differentiator circuit 31. be. FIG. 5 is a curve showing the output of the difference circuit 29, that is, the difference frequency and the output voltage, ₁ and ₂ are frequencies regarded as pseudo pull-in frequencies, and Vh and Ve are threshold voltages of the discrimination circuit 36.

In the figure, 21 is a hybrid circuit that branches the input signal into two, 22 and 23 are phase detectors, 24 is a baseband processing circuit such as a Costas-Slube type, 25,
26 is a differentiation circuit, 27 and 28 are mixing circuits, 29 is a difference circuit, 30 and 33 are low frequency circuits, 31 is a differentiation circuit, 32 is an amplifier, 34 is a voltage controlled oscillator, 3
5 is a 90° phase shifter, and 36 is a discrimination circuit.

The regenerated carrier wave output from the voltage controlled oscillator 34 is applied directly to the phase detector 22 and to the phase detector 23 via the 90° phase shift circuit 35, and the 4-phase PSK of the input signal split into two by the hybrid circuit 21 is applied to the phase detector 23.
Phase detection of the modulated wave is performed and applied to the baseband processing circuit 24.

Let ωd be the difference between the oscillation frequency of the voltage controlled oscillator 34 and the frequency of the 4-phase PSK modulated wave of the input signal, and let the outputs of the phase detectors 22 and 23 be sin(ωd・t
+θ)cos(ωd·t+θ), the outputs of the baseband processing circuit 24 are sin4(ωd·t+θ) and cos4(ωd·t+θ). Note that the baseband processing circuit is explained in detail in, for example, the Institute of Electronics and Communication Engineers Communication System Study Group document number CS74-42.

The differentiating circuits 25 and 26 are the baseband processing circuit 2
sin4(ωd・t+θ) and cos4(ωd・t
+θ) is differentiated and output,
Their differential outputs are: d/dt{sin4(ωd・t+θ)} =4ωd・cos4(ωd・t+θ)...(1) d/dt{cos4(ωd・t+θ)} =−4ωd・sin4(ωd・t+θ) ...(2). The mixing circuits 27 and 28 mix the output of the baseband processing circuit 24 and the differential output.
The outputs V ₁ and V ₂ are as follows: V ₁ =4ωd·cos ² 4 (ωd·t+θ) (3) V ₂ =−4ωd·sin ² 4 (ωd·t+θ) (4). The difference circuit 29 outputs the difference between the outputs V ₁ and V ₂ , and the difference output V is expressed as V=V ₁ −V ₂ =4ωd{cos ² 4(ωd・t+θ)+sin ² 4(
ωd・t+θ)}=4ωd...(5) That is, a signal obtained by multiplying the frequency difference ω _d by four is obtained.

The output V of the difference circuit 29 is the oscillation frequency of the voltage controlled oscillator 34 and the four-phase input signal as shown in FIG.
It becomes positive or negative depending on the magnitude of the frequency of the PSK modulated wave, and the output voltage of the low frequency converter 30 changes depending on the magnitude of the difference in frequency. The waveform of this output voltage is as shown in FIG. 4A and D, and _the determination circuit ₃₆ determines the voltage Vh,
Ve is the threshold voltage, and A is the positive threshold voltage Vh,
Let b be the negative side threshold voltage Ve. The output voltages of the low frequency converter 30 shown in A and D are the threshold voltages of A and B.
When Vh and Ve are exceeded, the discrimination circuit 36 outputs rectangular wave voltages as shown at F and E. This rectangular wave voltage is differentiated by a differentiating circuit 31, and only one of the differential outputs as shown in C and F {rise in diagram B, fall in diagram E} is output and applied as a control voltage to voltage controlled oscillator . The voltage controlled oscillator 34 operates by the isolated pulses shown at C and F so that the oscillation frequency becomes the center frequency. As a result, an automatic frequency control (AFC) loop is configured and pseudo-intraction can be prevented.

Also, the cos4 output of the baseband processing circuit 24
(ωd・t+θ) or sin4(ωd・t+θ) becomes the control voltage of the voltage controlled oscillator 34 via the amplifier 32 and the low-frequency amplifier 33, and this control voltage is the level between the input signal and the output of the voltage controlled oscillator 34. Since the value corresponds to the phase difference, a phase-locked loop (PLL) is constructed, and the output of the voltage controlled oscillator 34, that is, the regenerated carrier wave, can be obtained in synchronization with the input signal phase.

FIG. 6 is a circuit diagram of the main part of a voltage controlled oscillator,
51 is a variable capacitance diode, 52 is a capacitor,
53 is a coil, and 54 is an oscillation circuit, the oscillation frequency of which changes depending on the voltage applied to the variable capacitance diode 51. That is, the isolated pulse output from the differentiating circuit 31 has a polarity that corresponds to the positive or negative frequency difference ωd, and the control voltage output from the low frequency generator 33 has a polarity that corresponds to the positive or negative phase difference, and is variable. Since it is added to the capacitive diode 51 in a superimposed manner, the frequency difference ωd and the phase difference are controlled to be zero. This circuit is 4 times the frequency difference
4ωd is calculated, and when this frequency difference 4ωd exceeds the pseudo-entrainment frequencies ₁ and ₂ , the oscillation frequency of the voltage controlled oscillator 34 is set as the center frequency at the output of the differentiating circuit 31, so the release time from the pseudo-entraction becomes sufficiently early. . Furthermore, since the voltage controlled oscillator 34 in the phase-locked loop (PLL) is directly controlled, it can always be released from the pseudo pull-in. Moreover, the mixing circuit 2 of FIGS. 1 and 2
By calculating the difference between the output signals of 7 and 28, unnecessary signal components are canceled and only the frequency difference ωd component is obtained. Since this is used, stable frequency control is possible, and carrier wave regeneration by high-speed pull-in is possible. It becomes something that can be done. Further, although the above-mentioned embodiment is for a four-phase case, the present invention can also be applied to carrier reproduction for polyphase modulated waves such as two-phase, eight-phase, and 16-phase modulated waves.

As described in detail above, according to the present invention, it is possible to expand the pull-in range, prevent a false pull-in state, and perform normal phase pull-in at high speed.

[Brief explanation of the drawing]

1 and 2 are block diagrams of a conventional carrier wave recovery circuit, FIG. 3 is a block diagram of a carrier wave recovery circuit according to an embodiment of the present invention, and FIG. 4 is a low frequency amplifier 30 in the case of FIG. 3. , a time chart of the output waveforms of the discrimination circuit 36 and the differentiating circuit 31, FIG. 5 is a curve showing the output of the difference circuit 29, that is, a curve showing the relationship between the difference frequency and the output voltage, and FIG. 6 is a circuit diagram of an example of a voltage controlled oscillator. It is. In the figure, 1, 7, 22, 23 are phase detectors, 2,
24 is a baseband processing circuit, 3, 32 are amplifiers, 4, 30, 33 are low frequency generators, 5, 34 are voltage controlled oscillators, 6 is a crystal oscillator, 8 is a counter,
9 is a judgment circuit, 10 is a sweep circuit, 11 is a sum circuit,
21 is a hybrid circuit, 25, 26, 31 are differentiating circuits, 27, 28 are mixing circuits, 29 is a difference circuit,
35 is a 90° phase shifter, 51 is a variable capacitance diode,
52 is a capacitor, 53 is a coil, 54 is an oscillation circuit section, and 36 is a discrimination circuit.

Claims (1)

[Claims] 1. In a carrier wave regeneration circuit that controls the voltage controlled oscillator using a voltage corresponding to the phase difference between the input signal and the output signal of the voltage controlled oscillator as a control voltage, and synchronizes the oscillation frequency of the voltage controlled oscillator with the input signal. a differentiating circuit that differentiates the output signals of one and the other of the baseband processing circuits, a first mixing circuit that adds the differentiated signal of the one output signal and the other output signal, and a first mixing circuit that adds the differential signal of the one output signal and the other output signal; a second mixing circuit that adds the differential signal and the one output signal; a difference circuit that outputs the difference between the output signals of the first and second mixing circuits; and a difference circuit that outputs the difference between the output signals of the first and second mixing circuits; A carrier wave regeneration circuit comprising: a discrimination circuit that discriminates and outputs the discrimination circuit; and a circuit that differentiates the output of the discrimination circuit using a differentiating circuit, generates an isolated pulse, and uses the isolated pulse as a control voltage for the voltage controlled oscillator. .