JPH0552103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a PSK demodulation circuit for demodulating a two-phase PSK modulated signal.

(b) Prior Art Conventionally, a circuit using a Costas loop is known as a circuit for demodulating a PSK modulated signal.

A demodulator using this kind of Costas loop will be explained with reference to FIG. In Figure 4, 1
is a voltage controlled oscillator (VCO) that outputs a reference carrier signal, 2 is a first multiplier that multiplies the input PSK signal and the reference carrier signal from VCO 1, and 3 is connected to the output terminal of the first multiplier 2. 4 is a second multiplier that multiplies the input PSK signal by the reference carrier signal from VCO 1 whose phase has been shifted by 90° in 90° phase shift circuit 5; 6 is a second multiplier 4; 7 is a third multiplier that multiplies the outputs from LPFs 3 and 6; 8 is a loop filter connected to the output of the third multiplier 7; is connected to VCO1.

Here, the reference carrier signal from VCO1 is
cosωt, two-phase modulated signal ±Acos (ωt+φ), reference carrier signal cosωt and input signal ±Acos
The output of the first multiplier 2 that multiplies (ωt+φ) is
±A/2 [cosφ+cos(2ωt+φ)], and the reference carrier signal sinωt and the input signal ±Acos are phase-shifted by 90°.
(ωt+φ) The output of the second multiplier 4 is ±
A/2 [sinφ+sin(2ωt+φ)].

The outputs of each multiplier become ±A/2cosφ and ±A/2sinφ by passing through LPFs 3 and 6, respectively.

The outputs of the LPFs 3 and 6 are multiplied by a third multiplier 7, and an output A ² /4sin2φ is taken out. After this output passes through loop filter 8, VCO1
The oscillation frequency of VCO1 is controlled accordingly.

Thus, VCO1 will track the input carrier and PSK information will be obtained from the output of LPF3.

A demodulator using a Costas loop is disclosed in, for example, ``Spread Spectrum Communication System'' published by Jatec Publishing.

(C) Problems to be Solved by the Invention According to the demodulator using the Costas loop described above, it is possible to demodulate a PSK modulated signal.

However, since the Costas loop, which is a composite PLL, is used, there are problems in that the circuit configuration becomes complicated and the cost increases.

(d) Means for Solving the Problems In view of the above points, the present invention provides a narrowband bandpass filter whose center frequency is the carrier frequency of a PSK signal, and a detector that performs envelope detection of the output of this bandpass filter. and an inverting circuit whose output is inverted in response to a change in the detection output of the detector, and the output signal of the inverting circuit is used as a demodulated signal.

(E) Effect According to the present invention, the phase of the PSK signal is determined by passing the PSK communication through a narrowband bandpass filter whose center frequency is the carrier frequency of the PSK communication, and by performing envelope detection of the passed signal. A change point is extracted, and the output level of the inversion circuit is inverted every time a phase change occurs. Thus,
The PSK signal is demodulated.

(F) Embodiment FIG. 1 is a diagram showing an embodiment of the present invention. In the figure, 10 is an input terminal to which a two-phase modulated signal (BPSK signal) is applied, and 11 is a narrow band bandpass filter having the carrier frequency of the BPSK signal, which is composed of a crystal filter and has a pass band. The width is approximately 2KHz, as is clear from the characteristic diagram in FIG. Reference numeral 12 denotes a detector that detects the envelope of the signal that has passed through the bandpass filter 11, and is composed of, for example, a diode 13, a capacitor 14, and a resistor 15. 16 is detector 1
A waveform shaping circuit 17 shapes the waveform of the output of the waveform shaping circuit 16, that is, an inverting circuit whose output is inverted according to changes in the output of the wave detector 12. For example, the output of the waveform shaping circuit 16 is clocked (CLK). ) terminal, and a D flip-flop whose terminal is connected to the D terminal. 18 is an output terminal.

Next, the operation will be explained.

When a signal [Fig. 3 b] that has been two-phase modulated using the baseband data [Fig. 3 a] is applied to the input terminal 10, this two-phase modulated signal (BPSK signal)
passes through the bandpass filter 11 and becomes the signal shown in FIG. 3c.

That is, at the phase change point of the BPSK signal, the carrier wave becomes discontinuous and the frequency component drops instantaneously, resulting in a change in the carrier wave amplitude at the phase change point in relation to the passband width of the bandpass filter 11.

Such a change in the carrier wave amplitude is detected by the wave detector 12, and the detected output is as shown in FIG. 3d.

The detected output is waveform-shaped by the waveform shaping circuit 16 into a signal shown in FIG. 3c.

The inverting circuit 17 consisting of a D flip-flop is
It operates according to the output of the waveform shaping circuit 16.

That is, if it is assumed that the Q terminal output is at the L level and the detection output of the detector 12 changes to the L level at time ^t1 , the waveform shaping circuit 16 changes to a negative level in response to the change in the detection output. Outputs trigger pulse.

The inverting circuit 17 latches the D terminal input (ie, terminal output) in response to the fall of the negative trigger pulse, and inverts the Q terminal output to H level.

Furthermore, when a negative trigger pulse is output from the waveform shaping circuit 16 at time ^t2 , the D terminal input (L level) is latched in response to the falling edge of the negative trigger pulse, and the Q terminal output becomes L level.

In this way, the inverting circuit 17 inverts its output every time a negative trigger pulse is output, that is, every time the amplitude of the signal passing through the narrowband bandpass filter 11 changes due to a change in the phase of the carrier wave, as shown in FIG. As shown in FIG. 3, the signal shown in FIG. 3a is demodulated.

When the BPSK signal is first applied, the presence or absence of a phase shift in the carrier wave frequency is detected, and the initial setting of the inverting circuit (i.e., if there is no phase shift, the Q terminal output is set to L level, and if there is a phase shift, the Q terminal output is set to L level). , sets the Q terminal output to H level). Detection of such a phase shift is a well-known structure, so illustration and description thereof will be omitted.

(G) Effects of the Invention According to the present invention, there is provided a narrowband bandpass filter whose center frequency is the carrier frequency of PSK communication, a detector for envelope-detecting the output of this bandpass filter, and a detector for detecting an envelope of the output of this bandpass filter. The present invention includes an inverting circuit whose output is inverted according to a change in the detection output, and the output signal of the inverting circuit is used as a demodulation signal, so that the circuit configuration can be simplified and costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram of a band pass filter, FIGS. 3 a to 3 f are diagrams showing waveforms of various parts, and FIG. 4 is a diagram showing a conventional example. 10...Input terminal, 11...Band pass filter, 12...Detector, 16...Waveform shaping circuit,
17...Inversion circuit.

Claims (1)

[Claims] 1 A PSK demodulation circuit for demodulating a PSK (phase, shift, keying) modulated signal, which includes a narrowband bandpass filter whose center frequency is the carrier frequency of the PSK signal, and an output of this bandpass filter. A PSK comprising a detector that performs envelope detection and an inverting circuit consisting of a D flip-flop whose output is inverted according to a change in the detection output of the detector, and the output signal of the inverting circuit is used as a demodulation signal. Demodulation circuit.