JPH02131027A - Intermediate frequency signal processing circuit for receiver - Google Patents

Abstract

PURPOSE:To facilitate the reduction in the influence due to temperature and adjustment of modulation by mixing a 2nd intermediate frequency signal with a 3rd intermediate frequency signal generated through the mixture of the 1st and 2nd intermediate frequency signals to obtain an intermediate frequency signal of the same frequency as that of the 1st intermediate frequency signal and sending the result to an FM detector. CONSTITUTION:The 1st IF signal via an IF filter 11 is fed to a mixer 12, in which the signal is mixed with a 4.5MHz signal being an oscillated output of an oscillator 13 and the 3rd IF signal component of 6.2MHz (=10.7-4.5) is extracted from the output of the mixer 12 by a BPF 14. Transmission distortion generated from the IF filter 11 is included in the 3rd IF signal. The frequency spectrum of the 1st IF signal being one input to the mixer 2 is only the modulation component S. Thus, the modulation component S is led out as the output of the mixer 8 and distortion component is eliminated. Thus, the selectivity characteristic of the BPF 7 being IF filter is improved and the production of signal generation caused thereby is prevented.

Description

TECHNICAL FIELD The present invention relates to an intermediate frequency signal processing circuit for a receiver, and more particularly to an intermediate frequency signal processing circuit for an FM receiver.

BACKGROUND ART As an intermediate frequency signal processing circuit for an FM receiver, a circuit based on a system called a so-called non-spectrum IF system, which can easily reduce distortion, is shown in FIG. In FIG. 3, a first intermediate frequency signal of, for example, 10.7 MHz (hereinafter referred to as an IF multiplied signal) generated by the front end 1 is supplied to a mixer 2 and mixed with the output of a vCO (voltage controlled oscillator) 3. Ru. The output of an FM detector 4 is supplied to the control input terminal of vCO3 via an amplifier 5 and an LPF (low pass filter) 6. The free running frequency of vCO3 is, for example, 6.
2 MHz, and the frequency of the output of vCO3 is modulated around this free-running frequency according to the low frequency component of the output of the FM detector 4.

BPF (band pass filter) 7 from the output of mixer 2
The second IF signal component of 4.5 MHz (=10.7-6.2) is extracted. The second IF multiplied signal (4.5MHz) by this BPF7 is the output of vCO3 (6,2
MHz) is mixed in the mixer 8, and the IF filter 9
Then, the signal becomes the first IF multiplied signal (10.7 MHz) again and is supplied to the FM detector 4.

In the above configuration, the output of the VCOB is modulated around a free-running frequency of 6.2 MHz according to the low frequency component of the output of the FM detector 4. The frequency spectrum of the FM signal output from this VCOB is expressed by the original modulation signal S, which includes this VCOB, FM detector 4, amplifier 5, and LPF 6.
If the distortion generated by the transmission system is expressed as D, then (S + D)
Contains the following ingredients.

The first IF multiplied signal (10.7MHz) supplied to the mixer 2 together with the output of this VCOB is a BP signal that causes distortion.
Since the signal does not pass through an F (band pass filter) or the like, its frequency spectrum consists of only the S component. Therefore, B.P.
The second IF multiplied signal (4.5MHz) by F7 includes (S
Only the component 10D)-8=D, that is, the distortion component, exists. The second IF multiplied signal containing only this distortion component has a small frequency shift, so even if the BPF 7 is set to a narrow band to remove the interference component, no distortion will occur in the BPF 7.

Since a component (S+D)-D=S is derived as a conversion output of the mixer 8 to which the output of the VCOB and the output of the BPF 7 are supplied, the distortion component is removed. Therefore, the IF filter 9 can be a wideband filter that does not cause distortion.

Therefore, it is possible to improve the selectivity characteristics of the BPF 7, which is the F filter, and to prevent signal distortion caused by this.

In the above configuration, the V
Remodulation is performed by COB to generate FM waves, and this F
The IF multiplied signal spectrum is compressed using the mixer 2 using the M wave, and the IF multiplied signal spectrum that has passed through the 1F filter is restored to its original state by the mixer 8, thereby preventing the occurrence of distortion and increasing the selectivity of the IF stage. It can also be said that it is improving.

In the conventional IF signal processing circuit as described above, when the band of the IF filter BPF7 is narrowed to improve the selectivity characteristics, the temperature dependence of the VCOB is There is a need to reduce gender. However, since VCOBs generally have a configuration in which the oscillation frequency is made variable using a varicap, the V
It has been difficult to reduce the temperature dependence of COB. Another problem is that the degree of modulation of the FM signal output from the VCOB is difficult to adjust because it cannot be saboted.

Summary of the Invention The present invention has been made in view of the above points, and includes:
It is an object of the present invention to provide an intermediate frequency signal processing circuit for a receiver that is not easily affected by temperature and is easy to adjust.

In the intermediate frequency signal processing circuit of the receiver according to the present invention, a component of the first intermediate frequency signal that has passed through the bandpass filter and a signal of a predetermined frequency are mixed to generate a second intermediate frequency signal, 2 intermediate frequency signals are mixed to generate a third intermediate frequency signal, the second and third intermediate frequency signals are mixed to obtain an intermediate frequency signal having the same frequency as the first intermediate frequency signal, and FM detection is performed. I am trying to send it to a container.

EXAMPLES Hereinafter, examples of the present invention will be described in detail with reference to FIGS. 1 and 2.

In FIG. 1, front end 1. Mixer 2°8, B
PF7. The FM detector 4 and the IF filter 9 are connected in the same way as the circuit shown in FIG. However, in this example, the first IF multiplied signal by the front end 1 is supplied not only to the mixer 2 but also to the IF filter 11.

The IF filter 11 removes interference waves from the first IF multiplied signal.

Transmission distortion occurs in this IF filter 11.

1st IF multiplied signal 10°7MH after passing through 1F filter 1
z) is supplied to the mixer 12 and mixed with the 4.5 MHz signal which is the oscillation output of the oscillator 13. 6°2MHz (=10.7
=4.5) is extracted. This third IF multiplied signal contains transmission distortion generated in IF filter 1, and has a frequency spectrum of (S + D
) contains the following ingredients. This third IF multiplied signal is supplied to mixers 2 and 8.

Since the first IF multiplied signal frequency spectrum produced by the mixer 2 has only the S component, the second IF multiplied signal by BrF3 is (S + D) -5 as in the device shown in Fig. 3.
=D, that is, only the distortion component exists. Therefore, the output of the mixer 8 is (S+D)-D=
A component S is derived and the distortion component is removed.

Therefore, similarly to the circuit of FIG. 3, the IF filter Br
This makes it possible to improve the selectivity characteristics of F3 and to prevent signal distortion caused by this.

In the above-described IF signal processing circuit, the IF multiplied signal spectrum is compressed using the mixer 2 using the FM wave, and the IF multiplied signal spectrum that has passed through the IF filter is converted into the original signal by the mixer 8, as in the circuit shown in FIG. It can be said that the selectivity of the F stage is improved while preventing the occurrence of distortion by returning the FM wave to the narrow band IF filter to compress the spectrum of the 1F signal. It is obtained by converting the signal frequency twice. 4゜5 MH required for this IF multiplication signal frequency conversion
Since the oscillation frequency of the oscillator 13 that outputs the z signal is fixed, the temperature dependence can be easily reduced. In addition, there is no need to adjust the modulation degree,
Moreover, there is no need to consider temperature characteristics. Furthermore, since the oscillation frequency of the oscillator 13 is the same as the center frequency of the BrF3, no beat disturbance occurs.

In the circuit shown in FIG. 1, the signal delay of each part is not taken into consideration, and there is a possibility that the distortion generated in the IF filter 11 cannot be sufficiently canceled out.

FIG. 2 shows a circuit that compensates for signal delays in various parts and can sufficiently cancel out the distortion generated in the IF filter 11. In FIG. 2, front end 1. Mixer 2. s, 12°BrF3,14. F
M detector 4. The IF filter 9.11 and the oscillator 13 are connected in the same way as the circuit shown in FIG. However, in this example, a wideband IF filter 17 is connected between the front end 1 and the mixer 2. Further, the first IF multiplied signal that has passed through the IF filter 11 is supplied to the mixer 19 via the wideband IF filter 18 and mixed with the oscillation output of the oscillator 13. A third IF of 6.2MHz (=10.7-4°5) is generated from the output of the mixer 19 by BrF20.
The signal components are extracted and supplied to mixer 8.

In the above configuration, the IP filter 11 . The signal delay caused by mixer 12 and BrF 14 is compensated, and frequency conversion in mixer 2 is performed satisfactorily. Further, the signal delay caused by the BrF3 is compensated by the wideband IF filter 18, and the frequency conversion in the mixer 8 is performed satisfactorily. Therefore, the distortion generated in the IF filter 11 can be sufficiently canceled out.

Effects of the Invention As detailed above, in the intermediate frequency signal processing circuit of the receiver according to the present invention, the component of the first intermediate frequency signal that has passed through the bandpass filter and the signal of a predetermined frequency are mixed to produce the second intermediate frequency signal. , mix the first and second intermediate frequency signals to generate a third intermediate frequency signal, and mix the second and third intermediate frequency signals to generate a signal having the same frequency as the first intermediate frequency signal. Since the intermediate frequency signal is obtained and sent to the FM detector, vCO is not required and temperature dependence can be reduced, making it less susceptible to temperature effects. Further, at the same time, adjustment of the modulation degree by the VCO is not required, so adjustment is easy.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a block diagram showing another embodiment of the invention, and Fig. 3 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a block diagram showing an intermediate frequency signal processing circuit of a conventional receiver. Explanation of symbols of main parts 2, 8. 12. 19...Mixer 7.14.
20...BrF

Claims (1)

[Claims] a converting means for converting a frequency-modulated received signal into a first intermediate frequency signal, and a second intermediate frequency signal by mixing the bandpass filtered component of the first intermediate frequency signal with a signal of a predetermined frequency. mixing means for mixing the first and second intermediate frequency signals to obtain a third intermediate frequency signal; mixing means for mixing the second and third intermediate frequency signals to obtain the first intermediate frequency signal; An intermediate frequency signal processing circuit for a receiver, comprising mixing means for obtaining an intermediate frequency signal having the same frequency as a frequency signal and sending it to an FM detector.