JPH09298573A - Demodulation method and circuit demodulating quadrature amplitude modulation signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the demodulation circuit in which conversion of a received digital RF signal is not converted into an intermediate frequency signal and then which is not affected by the disturbance of the image frequency. SOLUTION: A digital RF signal including a quadrature amplitude modulation signal modulated by I and Q signals is received by a tuning circuit 12 and an amplifier 13 in the demodulation circuit. A voltage controlled oscillator 20 oscillates a conversion oscillation signal with the same frequency as that of the digital RF signal tuned by the tuning circuit. A 1st frequency mixer circuit 21 mixes the digital RF signal from the amplifier 13 with the converter oscillation signal oscillated by the voltage controlled oscillator to generate the I signal, and a 2nd frequency mixer circuit 23 mixes the digital RF signal from the amplifier 13 with the converter oscillation signal oscillated by the voltage controlled oscillator and shifted by 90 deg. at a phase shifter 22 to generate the Q signal and the quadrature amplitude modulation signal modulated by the I and Q signals is demodulated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulation method and a demodulation circuit for demodulating a digitally modulated signal having double sidebands such as QAM, and more particularly to quadrature amplitude modulation quadrature amplitude modulated by I and Q signals. The present invention relates to a demodulation method and a demodulation circuit that inputs a digital RF signal including a signal and demodulates an I signal and a Q signal from the input digital RF signal.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a conventional example of a demodulation circuit necessary for demodulating a quadrature amplitude modulation signal of this type (hereinafter abbreviated as QAM (Quadrature Amplitude Modulation) signal). The tuner section 100 of the demodulation circuit includes a signal input terminal 111, a tuning circuit 112, an amplifier circuit 113, a double tuning circuit 114, a frequency mixing circuit 115,
It is composed of a voltage controlled oscillator 116. Tuning circuit 1
12 is an input signal (RF
Of the signals), the amplifier circuit 113 cooperates with the double tuning circuit 114 to amplify the input signal tuned to the tuning circuit 112.

The voltage controlled oscillator 115 includes a tuning circuit 11
2, an intermediate frequency (for example, an intermediate frequency) higher than the input signal of the frequency to be amplified by the amplifier 113 and the double tuning circuit 114 (for example,
It oscillates at a frequency as high as 58.75 MHz). The frequency mixing circuit 116 inputs the output of the double tuning circuit 114 and the output of the voltage controlled oscillator 115, and converts the input signal into a low-frequency intermediate frequency signal by taking the difference between the two. In the above case, the tuning circuit 112 serves to prevent distortion from occurring in the amplifier circuit 113, and the double tuning circuit 114 is arranged to improve the characteristics relating to the image frequency interference generated in the frequency mixing circuit 116. ing.

Further, the intermediate frequency band filter 117 (hereinafter abbreviated as BPF 117) is a tuner 10.
An unnecessary component is removed from the output of 0, that is, the intermediate frequency signal output from the frequency mixing circuit 116, and only the desired intermediate frequency signal is output. The frequency mixing circuit 121 inputs the intermediate frequency signal that is the output of the intermediate frequency bandpass filter 117 and the output of the voltage controlled oscillator 120, and mixes them to generate an I signal. The 90 ° phase shifter 122 shifts the phase of the output of the voltage controlled oscillator 120 by 90 ° and outputs it. The frequency mixing circuit 123 receives the intermediate frequency signal output from the intermediate frequency bandpass filter 117 and the 90 ° phase shifter 1
The outputs of 22 and 90 ° phase-shifted outputs are respectively input and mixed to generate a Q signal.

[0005]

In the conventional demodulation circuit described above, an input signal (RF signal) is once converted into an intermediate frequency signal and then demodulated to obtain an I signal and a Q signal.
Thus, means for converting the input signal to an intermediate frequency signal include, for example, double tuned circuit 114, frequency mixing circuit 115, voltage controlled oscillator 116 and B.I. P. F117
Etc., the circuit is complicated, and image frequency interference is caused by the frequency mixing by the frequency mixing circuit 115 and the voltage controlled oscillator 116.

In view of the above problems, the present invention does not need to convert the input signal into an intermediate frequency signal in order to demodulate the input signal to obtain the I signal and the Q signal, and therefore the frequency for generating the intermediate frequency signal is not required. An object of the present invention is to provide a demodulation method and circuit which are not affected by image frequency interference due to mixing.

[0007]

In order to achieve the above object, the present invention inputs a digital RF signal including a quadrature amplitude modulation signal which is quadrature amplitude modulated by an I signal and a Q signal, and extracts from the input digital RF signal. In a demodulation method for demodulating an I signal and a Q signal, a conversion oscillation signal having the same frequency as an input digital RF signal is mixed with the input digital RF signal to generate an I signal, and the phase of the conversion oscillation signal Is shifted by 90 °, and the phase-shifted oscillation signal for exchange is mixed with the input digital RF signal to generate a Q signal.

Further, according to the present invention, a digital RF signal including a quadrature amplitude modulation signal quadrature amplitude modulated by an I signal and a Q signal is input, and I is input from the input digital RF signal.
In a demodulation circuit for demodulating a signal and a Q signal, an I signal demodulation means for generating an I signal by mixing a conversion oscillation signal having the same frequency as the input digital RF signal with the input digital RF signal, and the conversion signal. The phase of the oscillation signal is 9
And a Q signal demodulating means for generating a Q signal by mixing the input digital RF signal with the phase-shifted oscillation signal for phase shift by 0 °.

Further, according to the present invention, a signal input terminal for inputting a digital RF signal including a quadrature amplitude modulation signal quadrature amplitude modulated by an I signal and a Q signal, and a plurality of digital RF signals input to the signal input terminal. Desired digital R
A tuning circuit for selecting the F signal, an amplifier circuit for amplifying the desired digital RF signal selected by the tuning circuit, and a conversion oscillation signal having the same frequency as the frequency of the desired digital RF signal selected by the tuning circuit. A voltage-controlled oscillator that oscillates, a first frequency mixing circuit that mixes a desired digital RF signal selected by the tuning circuit and a conversion oscillation signal that the voltage-controlled oscillator oscillates to generate an I signal; The phase of the conversion oscillation signal oscillated by the voltage controlled oscillator is set to 9
A 90 ° phase shifter for shifting the phase by 0 °, a desired digital RF signal selected by the tuning circuit, and a conversion oscillation of the voltage controlled oscillator with the 90 ° phase shifter for shifting the phase by 90 °. A second frequency mixing circuit that mixes the signals with each other to generate a Q signal.

A demodulation method and circuit for demodulating a quadrature amplitude modulation signal of the present invention inputs a digital RF signal including a quadrature amplitude modulation signal quadrature amplitude modulated by an I signal and a Q signal, and is the same as the input digital RF signal. Mix the oscillation signal for frequency conversion with the input digital RF signal,
I signal is generated and the phase of the conversion oscillation signal is set to 9
The phase is shifted by 0 ° and the phase-shifted oscillation signal for exchange is mixed with the input digital RF signal to generate a Q signal. Therefore, without converting the input digital RF signal into an intermediate frequency signal, the digital RF signal is directly demodulated to generate the I signal and the Q signal.

[0011]

Next, an embodiment of the present invention will be described. FIG. 1 is a block diagram showing a configuration of a demodulation circuit according to an embodiment of the present invention. The signal input terminal 11 is a quadrature amplitude modulation signal (QAM) that is quadrature amplitude modulated with an I signal and a Q signal from a CATV transmission cable or the like.
(Quadrature Amplitude Moduration) signal)
A digital input signal (digital RF signal) including is input. The tuning circuit 12 tunes to a digital input signal of a desired frequency among digital input signals input from the signal input terminal 11 and extracts a desired digital signal. Amplifier circuit 1
3 amplifies the digital input signal tuned to the tuning circuit 12.

The voltage controlled oscillator 20 oscillates a conversion oscillation signal having the same frequency as the carrier wave of the digital input signal. The frequency mixing circuit 21 inputs the digital RF signal that is the output of the amplifier 13 and the conversion oscillation signal that is the output of the voltage controlled oscillator 20, and mixes them to generate the I signal. The 90 ° phase shifter 22 shifts the phase of the conversion oscillation signal from the voltage controlled oscillator 20 by 90 ° and outputs it. The frequency mixing circuit 23 outputs the digital RF signal output from the amplifier 13 and the output 90 ° from the 90 ° phase shifter 22.
The phase-shifted conversion oscillation signals are input and mixed to generate a Q signal.

In the case of CATV or the like, the frequency mixing circuit 21,
The I and Q signals generated by 23 are transmitted to subsequent circuits and used for data processing (not only for transmission of image signals and audio signals but also for various data transmission, for example, 16QAM or 64QAM). Used for data transmission).

As described above, in the demodulation circuit for demodulating the quadrature amplitude modulation signal of this example, the digital RF signal including the quadrature amplitude modulation signal quadrature amplitude modulated by the I signal and the Q signal is input to the signal input terminal 11 and tuned. Circuit 12, amplifier 1
A voltage-controlled oscillator 20 oscillates a conversion oscillation signal having the same frequency as that of the input digital RF signal, and mixes the generated conversion oscillation signal with the input digital RF signal by a frequency mixing circuit 21. Then, the I signal is generated. At the same time, the phase of the conversion oscillation signal from the voltage controlled oscillator 20 is shifted by 90 ° in the phase shifter 22, and the 90 ° phase-shifted replacement oscillation signal is input by the frequency mixing circuit 23 to the digital input signal. The Q signal is generated by mixing with the RF signal.

As is apparent from the above-described example shown in FIG. 1, the digital RF signal amplified by the amplifier 13 is not converted into the intermediate frequency signal, but the frequency mixing circuit 2 is not converted.
1 and 23 directly demodulate the digital RF signal into I and Q signals. Therefore,
Compared to the conventional demodulation circuit of FIG. 2, a part for converting to an intermediate frequency (double tuning circuit 114, voltage controlled oscillator 115,
The frequency mixing circuit 116 and the bandpass filter 117) are deleted, and the entire circuit is simplified. Further, since the digital RF signal is not converted to the intermediate frequency, it is also possible to avoid receiving the image frequency interference generated by the intermediate frequency conversion. In the above example, the input signal is applied to the signal input end 11, but an antenna may be connected to the signal input end 11 to receive transmission by microwaves or the like.

[0016]

As described above, according to the present invention, a digital RF signal including a quadrature amplitude modulation signal quadrature amplitude modulated by an I signal and a Q signal is input, and a conversion oscillation having the same frequency as the input digital RF signal is input. The signal is mixed with the input digital RF signal to generate the I signal, and
The phase of the conversion oscillation signal is shifted by 90 °, and the phase-shifted oscillation signal for exchange is mixed with the input digital RF signal to generate a Q signal, so that the input digital RF signal is intermediate. Without a circuit to convert to a frequency signal,
There is an effect that the digital RF signal can be directly demodulated to generate the I signal and the Q signal. Moreover, since the input digital RF signal is not converted into the intermediate frequency signal, the image frequency interference due to the conversion is received. There is also the effect that there is no.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a demodulation circuit according to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional demodulation circuit.

[Explanation of symbols]

11 ... Signal input terminal, 12 ... Tuning circuit, 13 ... Amplifier, 20 ... Voltage controlled oscillator, 21 ... Frequency mixing circuit, 23 ... Frequency mixing circuit.

Claims (5)

[Claims] 1. A demodulation method for inputting a digital RF signal including a quadrature amplitude modulation signal quadrature amplitude modulated by an I signal and a Q signal, and demodulating the I signal and the Q signal from the input digital RF signal. A conversion oscillation signal having the same frequency as the RF signal is mixed with the input digital RF signal to generate an I signal, the phase of the conversion oscillation signal is shifted by 90 °, and the phase is shifted. Digital RF input with oscillation signal
A demodulation method for demodulating a quadrature amplitude modulation signal, which is characterized by mixing with a signal to generate a Q signal. 2. The mixing for generating the I signal and the Q signal is performed by inputting a plurality of digital RF signals, selecting a desired digital RF signal from the digital RF signals, and selecting the desired digital RF signal from the selected digital RF signals. The demodulation method for demodulating a quadrature amplitude modulation signal according to claim 1, wherein the demodulation method is performed as follows. 3. A demodulator circuit for inputting a digital RF signal including a quadrature amplitude modulation signal quadrature amplitude modulated by an I signal and a Q signal, and demodulating the I signal and the Q signal from the input digital RF signal. An I signal demodulation unit that mixes a conversion oscillation signal having the same frequency as the RF signal with the input digital RF signal to generate an I signal, and shifts the phase of the conversion oscillation signal by 90 ° and shifts the phase. The digital RF input with the converted oscillation signal
A demodulation circuit for demodulating a quadrature amplitude modulation signal, comprising: a Q signal demodulation unit that mixes with a signal to generate a Q signal. 4. A selection for inputting a plurality of digital RF signals in front of the I signal demodulating means and the Q signal demodulating means for respectively generating the I signal and the Q signal, and selecting a desired digital RF signal from the plurality of digital RF signals. 4. A demodulation circuit for demodulating a quadrature amplitude modulation signal according to claim 3, further comprising means and amplification means for amplifying a selected desired digital RF signal. 5. A signal input end for inputting a digital RF signal including a quadrature amplitude modulation signal quadrature amplitude modulated by an I signal and a Q signal, and a desired digital RF from a plurality of digital RF signals input to the signal input end. A tuning circuit for selecting a signal, an amplifier circuit for amplifying a desired digital RF signal selected by the tuning circuit, and an oscillation signal for conversion having the same frequency as the frequency of the desired digital RF signal selected by the tuning circuit. A voltage controlled oscillator, a first frequency mixing circuit that mixes a desired digital RF signal selected by the tuning circuit and a conversion oscillation signal oscillated by the voltage controlled oscillator to generate an I signal; A 90 ° phase shifter for shifting the phase of the conversion oscillation signal oscillated by the controlled oscillator by 90 °, and a desired digital RF signal selected by the tuning circuit. The 90 ° phase shifter has a second frequency mixing circuit that mixes with the conversion oscillation signal of the voltage controlled oscillator whose phase is shifted by 90 ° to generate a Q signal. A demodulation circuit that demodulates a quadrature amplitude modulation signal.