JPS63250248A - Polyphase phase demodulator - Google Patents

Abstract

PURPOSE:To enhance the improvement of the S/N of a service channel (SC) signal by sampling only signal in a specified part of a control signal generated by multiplying a base band signal obtained by DC-AC detecting a polyphase phase modulated wave and adding it to a voltage controlled oscillation part. CONSTITUTION:In the case of transmitting the service channel(SC) signal such as an order signal and a monitoring signal, etc., only control signal in the specified part, that means the part of a normal phase state, of the control signal is sampled by a sampling means 4 by using a clock outputted from a multiplier 3 in order to be added to the voltage controlled oscillator 2. Therefore the C/N of the control signal can be improved. Thus, the S/N of the SC signal and the deterioration of the error rate of a main signal can be improved.

Description

[Detailed Description of the Invention] [Summary] In a polyphase phase demodulator, only a predetermined portion of a control signal generated by multiplying a baseband signal obtained by quadrature detection of a polyphase phase modulated wave is generated. By sampling and applying it to the voltage controlled oscillator, the C/N of the control signal is
The aim is to improve this.

[Industrial application field]

The present invention relates to an improvement of a polyphase phase demodulator 1, for example, a polyphase phase demodulator used in a digital multiplex radio device.

Service channel signals (hereinafter referred to as S
When transmitting a carrier wave (abbreviated as C signal), on the transmitting side, the carrier wave is shallowly frequency modulated with the SC signal, and then further subjected to, for example, four-phase phase modulation with the main signal, and then sent to the receiving side.

On the receiving side, the main signal and SC signal are extracted from the 4-phase phase modulated wave (hereinafter abbreviated as 4-phase PSK wave) received by the 4-phase phase demodulator, but at this time, the signal-to-noise ratio of the SC signal, etc. It is necessary to improve this.

C. Prior Art] Fig. 3 is a block diagram of a conventional example, Fig. 4 is an explanatory diagram of the configuration of the quadrupling circuit in Fig. 3, Fig. 4(a) is a circuit that obtains an output of 5in2ωt, Fig. 4 fb) shows a circuit that obtains an output of cos2ωt. Note that 1 is a quadrature detection section and 2 is a voltage controlled oscillation section.

The operation of FIG. 3 will be described below with reference to FIG. 4, taking the case of four-phase phase modulation as an example.

The input 4-phase PSK wave is distributed by the in-phase hybrid 11 and applied to the synchronous detector 12.13, where the output of the voltage controlled oscillator (hereinafter abbreviated as VCO) 22 is transmitted via the 90-degree hybrid 23. Therefore, the Ich and Qch baseband signals are extracted by synchronous detection.

This baseband signal is transmitted through low-pass filters 14 and 1.
5, a part of the signal is sent to the outside via amplifiers 16 and 17, and the remaining part is added to the quadruple multiplier 3 to be multiplied by four.The configuration of this quadruple multiplier will be schematically explained with reference to FIG.

Now, if ωt J, then by the addition theorem, 5in2A=
'A CCs1nA +cosA)") 'A C
C5jnA −cosA)”) cos2A= (cos28) (sin”A
), a double wave of the input wave can be obtained by the circuit shown in Fig. 4 (al, (b)).Then, by further passing this double wave through a double multiplier circuit, a 5in4
A quadrupled wave of A and cos4A is obtained, and the phase uncertainty is removed. Note that the absolute value circuit is used as a square circuit.

That is, if the 4th harmonic wave is 5in4ωtmye, then e is 5in
4(ωct-ωct'+θ, θ.+nπ/2)...(1
).

Here, ωct+ω, / is the respective carrier wave angular frequency, θ is the phase of the unmodulated wave on the transmitting side, and θ. is the phase of the VCO, nπ/2 is the phase term that changes due to four-phase phase modulation, and n is 0. It is a random value among C2 and C3.

Further, the first and second terms of the formula (fl) are terms indicating a frequency difference of 1 phase difference.

Note that 31 is a subtracter, 32 is an adder, 33 to 36 are absolute value circuits, and 37 and 38 are differential amplifiers.

The quadrupled wave e obtained in this way (hereinafter referred to as a control signal) passes through the loop filter 21, and a part of it passes through the amplifier 24.
However, the remaining part is added to the VCO 22 so that the frequency difference and phase difference terms in equation (1) become 0 and only the nπ/2 term remains, that is, the transmitter The oscillation frequency is controlled so that the unmodulated wave and the oscillation frequency of the VCO are synchronized.

Also, the differentiator 51. The multiplier 52 is part of the automatic frequency control AFC, and the cos4ωt output from the quadruple multiplier is differentiated by the differentiator 51 to obtain -4ωsinωL, which is multiplied by the control signal 5in4ωt in the multiplier 52 to eliminate synchronization. At the time, the frequency difference ω between the input 4-phase PSK wave and vCO
An AFC voltage proportional to is taken out and used to control the VCO so that it enters a synchronized state.

[Problem that the invention seeks to solve]

Here, the problem will be explained with reference to the problem explanatory diagram in FIG.

First, as shown in the frequency spectrum diagram of the four-phase PSK wave in Figure 5 (al), the higher the clock frequency fek, the more f
, fck is away from the intermediate frequency flf, so the frequency spectrum is spread, and the power density per unit frequency (shaded area) decreases, but conversely, as fck decreases, the power density increases.

On the other hand, in Fig. 3 (7) VCO 22, quadrature detector 12.1
3. Low-pass filter 14.15.4 Multiplier 3. The loop composed of the loop filter 21 (hereinafter referred to as automatic phase control loop and abbreviated as PLL) is shown in FIG.
As shown by the dotted line, it is considered to be a band-pass filter with fLf as the center frequency, so the lower fck is, the more noise components remain in the loop.

Next, as shown in the phase transition diagram of the 4-phase PSK wave in Figure 5 (bl), there is a transition every clock, for example, from phase to B, from B to D2, etc., but the transition time is the same as that of the radio. If the bandwidth was infinite, it would be instantaneous.

The narrower the bandwidth, the longer it will be.

Here, the radio eliminates interference from other sources and also.

Since the bandwidth is limited in order to prevent interference from others, the transition time becomes long, and the phase state in the middle of the transition is input to the control signal from the multiplier 3 as a phase error signal.

That is, the control signal contains noise components remaining in the above loop and a phase error signal generated because the transition time is not instantaneous, and the control signal contains Similarly, there is a problem that the CAM of the control signal deteriorates.

Along with this, the S/N of the SC signal and the C of the regenerated carrier wave
AM deteriorates.

[Means for solving problems]

The above problems are solved by the polyphase phase demodulator shown in FIG. Reference numeral 4 denotes a sampling means that uses the clock extracted from the output of the multiplier 3 to sample only a predetermined portion of the control signal and sends it to the voltage controlled oscillator 2.

[Effect]

The present invention improves the CAM of the control signal by sampling the clock output from the multiplier 3 and adding it to vCO.

This also improves the deterioration of the S/N ratio of the SC signal and the error rate of the main signal.

〔Example〕

FIG. 2 shows a block diagram of an embodiment of the invention.

Note that the bandpass filter 41. Amplifier 42. The phase shifter 43.degree. 45 and the switch 44 are constituent parts of the sampling means 4, in which 1 is a quadrature detection section and 2 is a voltage controlled oscillation section. or,
The same reference numerals indicate the same objects throughout the figures.

Hereinafter, the present invention will be described in detail with reference to FIG. 2 with reference to FIG. 5(C) for the case of a four-phase PSK wave.

Generally, the transmission bandwidth of wireless devices is limited in order to make effective use of frequencies, so the quadrature detection unit l is used in the multiplier 3.
By multiplying the baseband signal extracted by 4 times, the control signal shown in FIG. 5(C) is obtained.

Also, the center frequency of the output of the multiplier 3 is the clock frequency fc
The clock component is extracted through a band-pass filter 41, the amplifier 42 is used to change the clock duty factor, and the shifter 43 adjusts the phase. This switch 44 is turned on at the position of point B.

Therefore, since the switch is turned on only near the 0 cross point in FIG. 5(C), that is, near the position of the normal phase state, A
A control signal corresponding to the width of the clock centering on the point is held by the loop filter 21 and applied to the VCO 22 to control the oscillation frequency.

Therefore, the control signal does not contain noise other than the part indicated by the dotted line in Fig. 5 fc), so the CAM of the control signal is improved.
Along with this, the deterioration of the S/N of the SC signal and the deterioration of the error rate of the main signal are improved.

Note that the switch 44 may be configured to convert the input control signal into a digital signal, and further convert it into an analog signal and apply it to the VCO.

In this case, since the control voltage is sampled at the rising point of the clock during A/D conversion, the noise contained in the control signal is is further reduced and the CAM of the control signal is further improved.

The above explanation was made using a 4-phase PSK wave, but for 8-phase PS waves, 16-phase PSK waves, etc., the number of transitional phase states increases, and the control signal of each normal phase state is sampled. Regarding that, 4-phase PSK
Needless to say, it is applied in exactly the same way as in the case of .

〔Effect of the invention〕

As described in detail above, according to the present invention, there is an effect that deterioration of the VCO control signal is improved.

This has the effect of improving the S/N of the SC signal.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is a block diagram of a conventional example, and Fig. 4 is a configuration explanatory diagram of the quadrupling circuit in Fig. 3. , FIG. 5 shows an explanatory diagram of the problem. In the figure, 1 is a quadrature detection section, 2 is a voltage controlled oscillation section, 3 is a multiplier, and 4 is a sampling means. Fuwa fifeQ low top g J7ri1y cut trgJ

Claims (1)

[Claims] The input polyphase phase modulated wave is quadrature detected by the quadrature detection section (1) using the output of the voltage controlled oscillation section (2), and the obtained baseband signal is output and multiplied by the multiplier (3). In the polyphase phase demodulator, which generates a control signal and controls the voltage-controlled oscillator so that the oscillation frequency is synchronized with the unmodulated wave on the transmitting side, the control signal is extracted from the output of the multiplier (3). A multi-phase phase demodulator characterized in that a sampling means (4) is added that uses a clock to sample only a predetermined portion of the control signal and sends it to the voltage controlled oscillator (2).