JPH05276208A - Demodulation system and demodulation circuit for radio signal - Google Patents

Abstract

PURPOSE:To perform the integration of the whole demodulation circuit. CONSTITUTION:A radio signal of high frequency band area received by an antenna 11 and via an amplifier circuit 12 and a first BPF 13 of wideband characteristic is converted to a signal of first IF band by using a signal with prescribed frequency by a first local oscillation circuit 31. Thence, the signal is converted to signals of second IF band of in-phase component and orthogonal component by further multiplying by a second signal with prescribed frequency of a second local oscillation circuit 33 with fixed oscillation frequency at multiplication circuit parts 18, 19 via a second BPF 32 of wideband characteristic and a distributor 17. Those signals of second IF band of in-phase component and orthogonal component are multiplied at multiplication circuit parts 36, 37 by using a third local oscillation circuit 38 with variable frequency so as to select a desired radio signal. Thereby, the signals of baseband area of in- phase component and orthogonal component can be obtained, and the data of normal in-phase component and orthogonal component can be obtained by eliminating the high frequency components of them and digitizing them via LPFs 22, 24 and A/D converters 23, 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio signal demodulation system and a demodulation circuit for demodulating a radio signal orthogonally modulated by a digital signal.

[0002]

2. Description of the Related Art Conventionally, as a demodulation method for demodulating a radio signal quadrature-modulated by a digital signal, a desired radio signal is first selected and a predetermined intermediate frequency signal (hereinafter referred to as "IF signal") is selected.
It is general that the IF signal is re-demodulated after that.

However, in order to select a desired radio signal from the received radio signals and convert it into an IF signal having a predetermined frequency, the frequency of the signal output from the local oscillation circuit for multiplying the received radio signal is received. The difference from the frequency of the desired radio signal must be the frequency of the IF signal. This means that the frequency of the radio signal desired to be received is f
If the frequency of the R and IF signals is fI, the frequency of the signal output by the local oscillator circuit is "fR + fI" or "fR-
fI ”.

Therefore, when a demodulation circuit capable of receiving and demodulating a plurality of types of radio signals having different frequencies is constructed based on this system, the local oscillation circuit is oscillated with a variable oscillation frequency such as a PLL frequency synthesizer. It must be composed of a circuit.

FIG. 2 shows the structure of a conventional demodulation circuit based on this method. In the figure, a radio signal received by an antenna 11 is amplified by an amplifier circuit (AMP) 12 with an appropriate amplification factor, and then a first band pass filter (BP).
F) Input to 13.

The first band-pass filter 13 has a wide band characteristic setting that allows signals in a predetermined frequency band to pass because it is necessary to pass a plurality of types of radio signals having different frequencies. The radio signal that has passed through the pass filter 13 is input to the multiplication circuit unit 14.

The multiplication circuit unit 14 multiplies the radio signal from the first bandpass filter 13 by the frequency signal sent from the first local oscillation circuit 15 whose oscillation frequency is variable and I
The signal is converted into an F band signal and input to the second bandpass filter 16.

The second bandpass filter 16 has a narrow band characteristic setting because it is necessary to pass only the IF signal of a specific frequency. The second bandpass filter, the multiplication circuit section 14 and the The local oscillation circuit 15 of No. 1 constitutes a frequency conversion unit.

That is, the radio signal received by the antenna 11, amplified by the amplifier circuit 12, and then passed through the wide band first band pass filter 13 is first passed through the multiplication circuit section 14 to the first signal.
Is multiplied by the frequency signal output from the local oscillation circuit 15 of
Although it is considered as an F band signal, this IF band signal is a predetermined IF signal.
If the frequency of the received radio signal is fR and the frequency of the frequency signal output from the first local oscillation circuit 15 is f0 only when the frequency of the signal is the same (fixed), the frequency of this IF band is Only when the frequency of the signal, that is, the frequency difference “| fR−f0 |” between the two signals is the frequency of the IF signal, the signal can be passed through the narrow band second bandpass filter 16. is there.

I passed through the second bandpass filter 16
The F signal is distributed into two paths by the distributor 17, and is input to the multiplication circuit section 18 through one path and the multiplication circuit section 19 through the other path.

In the multiplication circuit section 18, the IF signal is multiplied by the fixed frequency signal from the second local oscillation circuit 20 whose oscillation frequency is fixed to obtain the baseband signal of the in-phase component (I phase). After removing the high frequency components from the phase baseband signal through the low pass filter (LPF) 22,
It is digitized by the / D converter 23 to obtain normal I-phase data.

Further, in the multiplication circuit section 19, the π / 2 phase shifter 21
Second local oscillator circuit whose phase is shifted by half a period via
The IF signal is multiplied by the fixed frequency signal from 20 to obtain a quadrature component (Q phase) baseband signal, and the high frequency component is removed from the Q phase baseband signal through the low-pass filter 24 before A / D conversion. Digitized with converter 25 and a regular Q
Get phase data.

The signal output by the low-pass filter 22 and the signal output by the low-pass filter 24 are also sent to the automatic phase control circuit (APC) 26. The automatic phase control circuit 26 responds to both inputs by The output phase of the local oscillator circuit 20 of 2 is automatically adjusted.

[0014]

In the conventional demodulation circuit having the above-mentioned configuration, when the plural kinds of radio signals having different frequencies are received, the first local oscillation circuit 15 is set to P
It must be composed of an oscillation circuit whose oscillation frequency is variable, such as an LL frequency synthesizer. When the received wireless signal is a signal in a high frequency band such as a quasi-microwave band, it becomes difficult to integrate a local oscillation circuit having an oscillation frequency variable, which is configured by a PLL frequency synthesizer or the like.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radio signal demodulating method and a demodulating circuit which can easily integrate a demodulating circuit. It is in.

[0016]

That is, according to the present invention, a received radio signal is converted into an intermediate frequency band signal,
A desired radio signal is selected after obtaining a signal in the baseband. In a high frequency band, a local oscillation circuit with a fixed oscillation frequency is used, which is easier to integrate than a local oscillation circuit with a variable oscillation frequency. By using the local oscillation circuit whose oscillation frequency is variable with respect to the signal dropped to the baseband band, it is possible to easily integrate the entire demodulation circuit.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the circuit configuration, and since the basic configuration is the same as that shown in FIG. 2, the same portions are denoted by the same reference numerals and detailed description thereof will be omitted.

Thus, the radio signal received by the antenna 11, amplified by the amplifier circuit 12, and then passed through the wide band first band pass filter 13 has a first local portion whose oscillation frequency is fixed in the multiplication circuit portion 14. The signal is multiplied by the frequency signal output from the oscillator circuit 31, and then passes through the second bandpass filter 32 having the wideband characteristic setting similarly to the first bandpass filter, and the frequency of the signal in the first IF band is changed. To be converted.

The frequency of the signal in the first IF band differs depending on the frequency of the received radio signal, and is distributed to two paths by the distributor 17 in the next stage, and the multiplication circuit section 18 is used in one of the paths. To the multiplication circuit section 19 via the other path.

In the multiplication circuit section 18, the signal in the first IF band is multiplied by the frequency signal output from the second local oscillation circuit 33 whose oscillation frequency is fixed, and then the first and second band pass filters are used. Similarly, the signal passes through the third band-pass filter 34 having the wide band characteristic setting, and the second IF of the in-phase component is passed.
The frequency is converted into a band signal.

In the multiplication circuit section 19, the first IF
The band signal is multiplied by the frequency signal from the second local oscillation circuit 33 whose phase has been shifted by a half cycle via the π / 2 phase shifter 21, and thereafter, as in the case of the first to third band pass filters. The signal is passed through the fourth band-pass filter 35 for which the wide band characteristic is set and frequency-converted into a signal in the second IF band of orthogonal components.

Here, the second I of the in-phase component and the quadrature component
The F band signal also has a different frequency depending on the frequency of the received radio signal, and the second IF band signal of the in-phase component obtained by passing through the third band pass filter 34 is sent to the multiplication circuit unit 36. , The signal in the second IF band of the quadrature component obtained by passing through the fourth band pass filter is input to the multiplication circuit unit 37.

Both of the multiplication circuit units 36 and 37 are C (not shown).
A frequency signal output from the third local oscillator circuit 38 whose oscillation frequency is variably set according to the frequency of the radio signal desired to be received by the PU 35 and whose phase is also set is supplied.

Therefore, the multiplication circuit section 36 multiplies the frequency signal from the third local oscillation circuit 38 by the signal in the second IF band of the in-phase component that has passed through the third band-pass filter 34 to obtain the in-phase component. Of the in-phase component, the high-frequency component is removed from the base-band signal of the in-phase component through the low-pass filter 22, and then digitized by the A / D converter 23 to obtain in-phase component data.

Also in the multiplication circuit section 37, the frequency signal from the third local oscillation circuit 38 is multiplied by the signal in the second IF band of the quadrature component passed through the fourth bandpass filter 35 to obtain the quadrature component. The quadrature component base band signal is obtained, the high frequency component is removed from the quadrature component base band signal through the low-pass filter 24, and then digitized by the A / D converter 25 to obtain the quadrature component data.

The signal output from the low-pass filter 22 and the signal output from the low-pass filter 24 are also sent to the automatic phase control circuit 26. The automatic phase control circuit 26 responds to both inputs of the third local signal. The output phase of the oscillator circuit 38 is automatically adjusted.

According to the above configuration, the radio signal in the high frequency band received by the antenna 11 and passed through the amplifier circuit 12 and the first band pass filter 13 having the wide band characteristic is oscillated at the first local oscillation frequency. The signal of the predetermined frequency by the circuit 31 is used to convert it into a signal of the first IF band, and then, through the second bandpass filter 32 of wide band characteristic and the distributor 17, the multiplication circuit units 18 and 19 further oscillate frequencies. A signal having a predetermined frequency by the fixed second local oscillation circuit 33 is used for multiplication to convert the signal into a second IF band signal having an in-phase component and a quadrature component.

A frequency-variable third local oscillation circuit 38 is used so that the multiplication circuit units 36 and 37 select a desired radio signal for the signals in the second IF band of the in-phase component and the quadrature component. By performing multiplication with the baseband signals of the in-phase component and the quadrature component, the baseband signals of the in-phase component and the quadrature component are low-pass filtered 22, 24,
By the A / D converters 23 and 25, the data of the normal in-phase component and the quadrature component can be obtained. For example, if the frequency of the wireless signal desired to be received is fR, the fixed oscillation frequency of the first local oscillation circuit 31 is f1, and the fixed oscillation frequency of the second local oscillation circuit 33 is f2, the third oscillation frequency variable Local oscillator circuit 38
By setting the frequency of the signal output by the above to "fR-f1-f2", the radio signal desired to be received is selected and demodulated.

Therefore, the first local oscillator circuit 31 and the second local oscillator circuit 33 having a fixed oscillation frequency, which can be easily integrated, are used in the preceding stage of the demodulation circuit unit for processing signals in the high frequency band, and The signal dropped to the intermediate frequency band is converted into a baseband signal by using the third local oscillation circuit 38 with a variable oscillation frequency, and this is converted into a lowpass filter 22, 2.
4. Since the normal in-phase component and the quadrature component are converted into data by the A / D converters 23 and 25, the whole demodulation circuit can be easily integrated.

[0030]

As described above in detail, according to the present invention, a received radio signal is converted into an intermediate frequency band signal, and a desired radio signal is selected after obtaining a base band signal. In the high frequency band, a local oscillation circuit with a fixed oscillation frequency is used, which is easier to integrate than a local oscillation circuit with a variable oscillation frequency, and a local oscillation circuit with a variable oscillation frequency is used for signals dropped to the baseband. By doing so, it is possible to provide a radio signal demodulating method and a demodulating circuit that can easily integrate the entire demodulating circuit.

[Brief description of drawings]

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

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

[Explanation of symbols]

11 ... Antenna, 12 ... Amplification circuit, 13 ... First band pass filter, 14, 18, 19, 36, 37 ... Multiplication circuit section, 15, 31 ... First local oscillation circuit, 16, 32 ... Second Band pass filter, 17 ... Distributor, 20, 33 ... Second local oscillation circuit, 21 ... π
/ 2 phaser, 22, 24 ... Low-pass filter, 23,25 ... A /
D converter, 26 ... Automatic phase control circuit, 34 ... Third bandpass filter, 35 ... Fourth bandpass filter, 38 ... Third
Local oscillator circuit.

Claims (2)

[Claims] 1. After converting a received radio signal into a signal of a first intermediate frequency band using a signal of a first predetermined frequency,
A signal of the second intermediate frequency band of the in-phase component and a signal of the second intermediate frequency band of the quadrature component are obtained from the signal of the first intermediate frequency band by using the signal of the second predetermined frequency. The signal of the second intermediate frequency band and the signal of the quadrature component of the quadrature component are used to generate the baseband signal of the in-phase component and the quadrature component of the quadrature component by using the signal whose frequency is set according to the frequency of the radio signal to be received. A radio signal demodulation system characterized by performing A / D conversion of each of these after obtaining a baseband signal. 2. A first local oscillating means having a fixed oscillating frequency, and a first frequency converting means for multiplying a received radio signal by an output of the first local oscillating means to convert it into an intermediate frequency band signal. Distributing means for distributing the signal in the intermediate frequency band obtained by the first frequency converting means into two paths; second local oscillating means having a fixed oscillation frequency; In one of the paths, first signal processing means for multiplying the output of the second local oscillation means to obtain a signal in the second intermediate frequency band of the in-phase component, and the signal in the intermediate frequency band In the other of the two paths, a second signal that is multiplied by the output means of the second local oscillating means via the π / 2 phase shifter to obtain a signal in the second intermediate frequency band of the quadrature component. Processing means and third local part with variable oscillation frequency And a second intermediate frequency band signal of the in-phase component and the quadrature component obtained by the first and second signal processing means, respectively, is multiplied by the output of the third local oscillation means, A radio having a conversion means for converting into a baseband signal of a quadrature component and an A / D conversion means for A / D converting the baseband signals of the in-phase component and the quadrature component obtained by the conversion means. Signal demodulation circuit.