JPS61177054A - Receiving circuit of phase modulating signal - Google Patents

Abstract

PURPOSE:To reduce beat interruption and to reduce the number of oscillators by multiplying the frequency of an intermediate frequency signal N times to use the multiplied signal as an oscillation signal from a fixed station part and then dividing the N-multiplied frequency by N to use the N-divided signal as a reference carrier to be applied to a phase detector. CONSTITUTION:In a PSK receiving circuit 40, a frequency multiplier 41 multiplies the frequency of the 2nd intermediate frequency signal by N and applies the N-multiplied signal to a PLL circuit 42 as a reference frequency. When a modulation signal is M phases, the multiplier 41 multiplies the frequency by N which is integer times of M. A part of the output signal of the circuit 42 is divided by N by a frequency divider 46 and the N-divided signal is applied to a phase detector 8 as a reference carrier. Consequently, the phase of N-times frequency of said frequency is not influenced by PSK-modulated phase information. Since the signal is divided by N by the frequency divider 46, the reference carrier having the same frequency as that of the 2nd intermediate frequency signal and controlled at a fixed phase is outputted.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention converts a phase-modulated received signal into an intermediate frequency signal using a fixed local oscillation signal, and this intermediate frequency signal is given a reference carrier wave. The present invention relates to a receiving circuit for a phase modulated signal for phase demodulation using a phase detector.

(Prior art) In recent years, when transmitting digital signals using carrier waves such as very short waves and microwaves, PSK (Page 5h
Phase modulation methods such as the QAM (Quadrature Amplitude Modulation) method and the QAM (Quadrature Amplitude Modulation) method have been researched and put into practical use. On the other hand, for satellite communications, satellite broadcasting, CATV, etc.
At the same time that signals are digitized to improve the quality of images and audio, they are compressed to a lower bit rate,
Research is being conducted to compress the frequency bandwidth required for transmission. Therefore, - As an example, if a color television signal compressed to a low bit rate of 20 Mb/s is
If it is transmitted using the 6-phase PSK method or the 16-value QAM method, it becomes possible to transmit with a frequency bandwidth of 6 Mn2, which is equivalent to one channel of television broadcasting, which is required in conventional analog transmission. Therefore, digitized color television signals can be transmitted with the same channel density as conventional analog color television signals, which is extremely useful for CATV and the like.

Here, a block circuit diagram of a conventional PSK receiving circuit in which a phase modulated signal receiving circuit for phase demodulating a phase modulated color television signal is applied to a CATV converter using the PSK method is shown in FIG. The system shown in Figure 2 generates an intermediate frequency signal from a PSK modulated 50 to 550 M)+2 received signal using the double superhetero gain method, and uses the PSKf4I modulation circuit to generate an intermediate frequency signal from this intermediate frequency signal.
In FIG.
is mixed with a variable local oscillation signal provided from a variable local oscillator 3 that is variably adjusted depending on the channel to be received, and is mixed with a variable local oscillation signal provided from a variable local oscillator 3 that is variably adjusted depending on the channel to be received.
Two first intermediate frequency signals are extracted. This first intermediate frequency signal is applied to a second mixer 5 and mixed with a fixed local oscillation signal applied from a fixed local oscillator 6.
A second intermediate frequency signal of MH2 is generated. This second intermediate frequency signal is amplified by an IF amplifier 7 and a phase detector 8
is converted into phase information by the reference carrier wave provided from the carrier regeneration circuit 9. Furthermore, this phase information is given to the discriminator 10, and the clock synchronization circuit 11
The signal is identified at the correct timing by the clock signal provided from the , and is converted into a digital signal and provided to the digital signal processing circuit 12 . The digital signal processing circuit 12 demodulates the signal into an analog color television signal.

Here, the phase detector 8, the carrier regeneration circuit 9, and the discriminator 1
PSK consisting of 0 and clock synchronization circuit 11, etc.
The demodulation circuit 13 is a well-known technique, and various systems are known.Detailed explanation is omitted, but please refer to FIGS. 3 and 4 for the carrier regeneration circuit 9 related to the present invention. Its structure will be briefly explained. FIG. 3 is a block circuit diagram of a baseband processing type (Costas type) four-phase PSK signal carrier recovery circuit 9. Two phase information is output from the four-phase PSK phase detector 8, and these two phase information are output from the four-phase PSK phase detector 8. The phase information is provided to an addition circuit 21 and a subtraction circuit 22, respectively, and the outputs of these addition circuits 21 and subtraction circuits 22 are provided to a first exclusive OR circuit 23. Further, the two phase information of the phase detector 8 is given to the second exclusive OR circuit 24, and the outputs of the J$2 exclusive OR circuit 24 and the first exclusive OR circuit 23 are input to the third exclusive OR circuit 24. is applied to circuit 25. The output of the third exclusive OR circuit 25cr+ is supplied to the voltage controlled oscillator (C0) 27 after the harmonic components are removed by the low pass filter 2B. The voltage controlled oscillator 27 outputs a reference carrier wave having the same frequency as the second intermediate frequency signal and controlled to have a constant phase, and is provided to the phase detector 8.

Further, FIG. 4 is a block circuit diagram of the carrier regeneration circuit 9 of the frequency multiplication type 4-phase PSK @ signal, and the phase detector 8
The frequency of the second intermediate frequency signal given to the second intermediate frequency signal is frequency-multiplied by the quadrupling circuit 31 and converted into a signal of four times the frequency. The phase of this quadrupled frequency signal is not affected by the PSK modulated phase information, and the frequency of the output signal of this quadrupling circuit 31 is detected by
As the reference frequency of the PL and L circuits consisting of the low-pass filter 33 and the voltage-controlled oscillator 34, the voltage-controlled oscillator 34' outputs a quadrupled frequency controlled to have a constant phase. Furthermore, this four-times frequency is divided by a 4-frequency divider 35, and a reference carrier wave having the same frequency as the second intermediate frequency signal and controlled to a constant phase is outputted to the phase detector 8. It is configured to be given.

(Problems to be Solved by the Invention) The conventional PSK receiving circuit l described above includes a variable local oscillator 3 for generating an intermediate frequency signal from a received signal, a fixed local oscillator 6, and a carrier for PSK demodulation. An oscillator of the reproduction circuit 9 is required for each. and,
Since the frequencies output from these oscillators are not in an integer multiple relationship, beat interference is likely to occur due to mutual harmonic components.Also, compared to analog transmission using the conventional double super heterolog system, The number of oscillators for PSK demodulation increases by one, making it more difficult to take measures against some beat disturbances. Furthermore, since the number of oscillators for PSK demodulation increases by one, there are problems in that the manufacturing cost increases and the size increases accordingly.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the conventional phase modulation signal receiving circuit described above. By dividing the obtained frequency by N and using it as a reference carrier wave given to a phase detector, the frequency of a fixed local oscillation signal, etc. is set as an integral multiple of the frequency of the reference carrier wave, thereby reducing the occurrence of beat interference. Another object of the present invention is to provide a phase modulation signal receiving circuit that can be manufactured at low cost by reducing the number of oscillators.

(Means for Solving the Problem) In order to achieve the above object, the phase modulated signal receiving circuit of the present invention mixes the phase modulated received signal with a fixed local oscillation signal in a mixer to generate an intermediate frequency signal. A phase modulation signal receiving circuit that generates a signal and demodulates the phase of this intermediate frequency signal using a phase detector includes a frequency multiplier that multiplies the frequency of the intermediate frequency signal by N, and a frequency multiplier that multiplies the frequency of the output signal of the frequency multiplier. A PLL circuit that uses a reference frequency, and a frequency divider that divides the frequency of the output signal of the PLI and the circuit by N,
The output signal of the PLL circuit is used as a fixed local oscillation signal applied to the mixer, and the output signal of the frequency divider is used as a reference carrier wave applied to the phase detector.

(Function) The frequency of the intermediate frequency signal is multiplied by N and used as a fixed local oscillation signal, and this N-multiplied frequency is further divided by N and used as the reference carrier wave given to the phase detector, so the output from the mixer is The frequency of the fixed local oscillation signal is an integer multiple of the frequency of the intermediate frequency signal and reference carrier wave, which makes it possible to reduce beat interference due to mutual harmonic components of these frequencies. is easy. Furthermore, since a fixed local oscillator is not required, it can be manufactured at a lower cost and can be easily miniaturized.

(Description of Embodiments) Hereinafter, a first embodiment of the phase modulation signal receiving circuit of the present invention will be described.
This will be explained with reference to the figures. FIG. 1 is a block circuit diagram of an embodiment of a PSK receiving circuit in which the phase modulated signal receiving circuit of the present invention is applied to a CATV converter using the PSK method. In FIG. 1, circuits that are the same as those in FIG. 2 are designated by the same reference numerals, and redundant explanation will be omitted.

In FIG. 1, the PSK receiving circuit 40 according to the present invention multiplies the frequency of the second intermediate frequency signal from the IF amplifier 7 by N in a frequency multiplier 41, and the frequency of the output signal of the frequency multiplier 41 is set to PLL. It is applied to circuit 42 as a reference frequency. Here, if the PSK modulation signal is M-phase, the frequency multiplier 41 multiplies the frequency of the second intermediate frequency signal from the IF amplifier 7 by N, which is an integral multiple of M. In addition, PLL
As is well known, the circuit 42 includes a phase detector 43, a low-pass filter 44, and a voltage controlled oscillator 45. The output signal of this PLL circuit 42 is given to the second mixer 5 as a fixed local oscillation signal.

Furthermore, a part of the output signal of this PLL circuit 42 is frequency-divided by N by a frequency divider 46 and is given to the phase detector 8 as a reference carrier wave.

In such a configuration, the M-phase PSK modulated second
The frequency of the intermediate frequency signal is changed to M by the frequency multiplier 41.
Since the phase is multiplied by an integral number N, the phase of the frequency N times the frequency of the output signal of the frequency multiplier 41 is PSK
unaffected by the phase information being modulated,
Then, by dividing the frequency of the output signal of the frequency multiplier 41 by N by the frequency divider 4B, a reference carrier wave having the same frequency as the second intermediate frequency signal and controlled to have a constant phase is output. . This reference carrier wave is applied to the phase detector 8, and the PSK modulated signal is demodulated.

By the way, the first part of the PSK receiver circuit 40.

The frequency of the intermediate frequency signal and the second intermediate frequency signal is 50 to 5.
50MH2 (7) CATV signal (7) The frequency of the first and second intermediate frequency signals may be selected as appropriate values that do not cause image interference or beat interference. 5650 MB per 2 and 45
It is also possible to select by changing from MB2 by about several dozen MH2.

Therefore, for example, in the 16-phase PSK modulation method, the second
The frequency of the second intermediate frequency signal generated by the mixer 5 is set to 4.
If set to 3MH2, this frequency will be transmitted to the frequency multiplier 41.
The frequency is multiplied by 16 times and converted to a frequency of 688 MB2. Furthermore, the frequency of this 688 MB2 is changed to the PLL circuit 4.
2 to the second mixer 5 as a fixed local oscillation signal. Then, the frequency of the first intermediate frequency signal is changed from 688 MB2, which is selected as the frequency of the fixed local oscillation signal, to 43M, which is selected as the frequency of the second intermediate frequency signal.
645 MB2 with a difference of H2 is selected.

Furthermore, the frequency of the fixed local oscillation signal is divided into 1 by a frequency divider 48.
The frequency is divided by 6, converted into a 43 MB2 reference carrier wave, and applied to the 1-phase detector 8. The first and second selected in this way
The frequency of the intermediate frequency signal and the frequency of the fixed local oscillation signal have approximately the same relationship as the respective frequencies explained in FIG. 2, and do not have values that cause particular image disturbance or beat disturbance.

Therefore, the frequency of the fixed local oscillation signal is an integral multiple of the frequency of the second intermediate frequency signal and the reference carrier wave, and furthermore, the frequency of the first intermediate frequency signal is the same as that of the second intermediate frequency signal. It is an integral multiple of the frequency, so the occurrence of beat disturbance is reduced and countermeasures against it are easy. Further, a fixed local oscillator for generating a fixed local oscillation signal is not required, which makes manufacturing cheaper and easier to downsize.

In the above explanation, the PSK receiving circuit applied to a CATV converter using the PSK method was explained as an example, but the present invention is not limited to this, and signal receiving devices that convert frequencies using fixed local oscillators for satellite communication and satellite broadcasting etc. It may also be used for 8-phase PSK as a phase modulation method.
16-phase PSK, 32-phase PSK, and 16-level Q
Of course, AM or 256-value QAM modulation methods may also be used.

(Effects of the Invention) As explained above, the phase modulation signal receiving circuit according to the present invention multiplies the frequency of an intermediate frequency signal by N and uses it as a fixed local oscillation signal, and further uses the N-multiplied frequency by N. Since the frequency of the fixed local oscillation signal is divided and used as the reference carrier wave given to the phase detector, the frequency of the fixed local oscillation signal is an integral multiple of the frequency of the intermediate frequency signal and reference carrier wave output from the mixer. Beat interference due to mutual harmonic components of frequencies can be reduced, and measures against beat interference are easy. Further, since a fixed local oscillator is not required, it can be manufactured at a correspondingly low cost and has excellent effects such as easy miniaturization.

[Brief explanation of drawings]

FIG. 1 shows a phase modulation signal receiving circuit of the present invention in a CATV system.
FIG. 2 is a block circuit diagram of an embodiment of a PSK receiving circuit applied to a converter using the PSK method. FIG. 2 is a block circuit diagram of a conventional PSK receiving circuit applied to a CATV converter using the PSK method. FIG. 4 is a block circuit diagram of a carrier regeneration circuit for a four-phase PSK signal of baseband processing type, and FIG. 4 is a block circuit diagram of a carrier regeneration circuit for a one-frequency multiplication type four-phase PSK signal. 1.40: PSK receiving circuit, 5: second mixer, 8: phase detector, 41 = frequency multiplier, 42: PLL circuit, 4
8: Frequency divider.

Claims (1)

[Claims] In a phase modulated signal receiving circuit that mixes a phase modulated received signal with a fixed local oscillation signal in a mixer to generate an intermediate frequency signal, and phase demodulates this intermediate frequency signal in a phase detector, A frequency multiplier that multiplies the frequency by N, a PLL circuit that uses the frequency of the output signal of this frequency multiplier as a reference frequency, and a frequency divider that divides the frequency of the output signal of this PLL circuit by N, A receiving circuit for a phase modulated signal, characterized in that the output signal of the PLL circuit is used as a fixed local oscillation signal given to the mixer, and the output signal of the frequency divider is used as a reference carrier given to the phase detector. .