JPH0641408Y2 - PSK demodulation circuit - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a demodulation circuit using a Costas loop as a carrier recovery method for demodulating a four-phase PSK signal.
In particular, PSK has a function of determining whether the reproduced carrier wave is in a state of capturing the input carrier wave component of the 4-phase PSK demodulation circuit.
It relates to a demodulation circuit.

[Conventional technology and problems to be solved]

Conventionally, the 4-phase PSK demodulation circuit using the carrier recovery method by the coster's loop does not have a function to determine whether the reproduced carrier is in the state of capturing the input carrier component of the 4-phase PSK demodulation circuit, that is, in the synchronization state. .

For this reason, it is not possible to inform the operating operator of the operating status of whether the 4-phase PSK demodulator is operating normally, or to display the operating status on a display etc. to notify the operator. There was a flaw.

Therefore, a technical problem of the present invention is to provide a PSK demodulation circuit having a function of determining a carrier capture state that indicates whether the PSK demodulation circuit is operating normally.

[Means for Solving the Problems]

According to the present invention, the phase error voltage extracted by the Costas loop for reproducing the carrier wave of the 4-phase PSK demodulation circuit, that is, the voltage due to the phase difference of the reproduced carrier wave phase with respect to the phase of the input carrier wave component of the 4-phase PSK demodulator circuit is minimized. As a means for generating the maximum voltage in the phase difference, a multiplier different from the multiplier for the Costers loop configuration and a low-pass filter for removing an AC component from the multiplication result of this multiplier,
And a comparator for comparing the output of the low-pass filter with a reference voltage.

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 shows waveforms at various parts of the circuit shown in FIG. In this circuit, a multiplier 13 is added to a 4-phase PSK demodulation circuit that reproduces a carrier wave by the Costers loop method, and the voltage for determining the captured state of the reproduced carrier wave is extracted from the output of the multiplier 13 Is.

If the input signal of this 4-phase PSK demodulation circuit is E _cos (ωt + φ) and the regenerated carrier generated by the voltage controlled oscillator (hereinafter referred to as VCO) 3 is cos ωt, the output of the first phase demodulation multiplier 1 Is Ecos (ωt + φ) · cos (ωt). Expanding this, Ecos (ωt + φ) ・ cos (ωt) = E [cos ² ωt cosφ +
sin ωt ・ cos ωt ・ sinφ] = E / 2 [cos2ωt ・ cosφ
+ Cosφ + sin2ωt · sinφ]. The frequency components of the first and third terms of this equation are 2ω, and the components of these terms are removed by the first low-pass filter 5. As a result, the output of the first low-pass filter 5 becomes E / 2cosφ.

The reproduced carrier wave cos ωt which is the output of VCO3 is π / 2 phase shifter 4
By passing through, cos (ωt−π / 2) = sin ωt. Therefore, the output of the second phase demodulation multiplier 2 is Ecos
(Ωt + φ) · cos (ωt), which is expanded as follows.

Ecos (ωt + φ) ・ sin (ωt) = E [cos ωt ・ cosφ ・ sin ωt + sin ² ωt ・ sinφ] = E / 2 [sin (2ωt + φ) + sinφ-cos2ωt ・ sinφ] The first and third terms of this equation The frequency is 2ω, and the components of these terms are removed by the second low-pass filter 6. As a result, the output of the second low-pass filter 6 becomes E / 2sinφ.

The waveforms of the output E / 2cosφ of the first low-pass filter 5 and the output E / 2sinφ of the second low-pass filter 6 are as shown in FIGS. 2A and 2C, respectively. The signal shown in FIG. 2A is converted into the rectangular wave shown in FIG. 2B by the second limiter circuit 10 shown in FIG. Similarly, the signal shown in FIG. 2C is converted into the rectangular wave shown in FIG. 2D by the first limiter circuit 9 of FIG.

The input waveform of the third multiplier 7 in FIG. 1 is as shown in FIG.
(D), and the input waveform of the multiplier 8 in FIG. 4 is shown in FIGS. 2 (b) and 2 (c). as a result,
The output of the third multiplier 7 is as shown in FIG. 2 (e), and the output of the fourth multiplier 8 is as shown in FIG. 2 (f).

The adder 11 subtracts the output voltage of the fourth multiplier 8 from the output voltage of the third multiplier 7. That is, the output voltage of the adder 11 is obtained by subtracting the voltage of FIG. 2 (f) from FIG. 2 (e), and the voltage waveform thereof is as shown in FIG. 2 (g). The waveform shown in Fig. 2 (g) is 4-phase PSK.
This is a characteristic generally known as the phase error characteristic of the demodulation circuit. The phase stable point of the reproduced carrier wave by the costers loop is the point P of the waveform shown in FIG.

On the other hand, the output voltages of the third multiplier 7 and the fourth multiplier 8 are also supplied to the fifth multiplier 13 to carry out multiplication. That is, by multiplying the voltage waveforms shown in FIGS. 2E and 2F, the waveform shown in FIG. 2C is obtained as the output waveform of the fifth multiplier 13.

Comparing the waveform of FIG. 2 (g) with the waveform of FIG. 2 (h), the fifth multiplier 13 of the fifth multiplier 13 is at the minimum point of the voltage waveform of FIG. It turns out that the output voltage shows the maximum value. This shows that the maximum voltage can be output from the fifth multiplier 13 when the reproduced carrier wave by the Costas loop is in synchronization with the carrier wave component of the 4-phase PSK input signal.

The output signal of the fifth multiplier 13 is the third low-pass filter 14
Thus, the AC component is removed, and only the DC voltage is output as the output of the low pass filter 14. The DC output voltage of the low-pass filter 14 is compared with the reference voltage defined by the comparator 15, and the output of the comparator 15 makes it possible to determine the presence or absence of the voltage, that is, the capture state of the reproduced carrier wave.

[Effect of device]

According to the present invention, it is possible to determine whether the PSK demodulation circuit is operating normally by judging the capture state of the reproduced carrier wave, and use this signal to inform the other device of the operation state of the demodulation circuit. It can be displayed to the operator.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a signal waveform diagram of each part of FIG. 1,2,7,8,13 are multipliers, 5,6,14 are low-pass filters, 9 and 10 are limiter circuits, 11 is an adder, and 12 is a loop filter forming a Costers loop.

Claims (1)

[Scope of utility model registration request] 1. A PSK demodulation circuit for recovering a carrier wave by means of a costers loop, wherein first and second multipliers for phase demodulation which constitute the costers loop and these first and second multipliers are provided.
In addition to the third and fourth multipliers for detecting a phase error connected to each of the multipliers, the output signals of the third and fourth multipliers are used as inputs to perform multiplication, thereby performing phase synchronization. A fifth multiplier that outputs a maximum output voltage, a low-pass filter that is connected to the output of the fifth multiplier and removes an AC component included in the output of the fifth multiplier, and is connected to the low-pass filter. And comparing the direct current output voltage with a prescribed reference voltage to determine whether the output direct current voltage of the fifth multiplier is large or small, that is, a carrier capture state. PSK demodulator circuit.