JPS5928732A - Circuit for improving transmission distortion in if amplification - Google Patents

Abstract

PURPOSE:To improve the transmission distortion without causing any deterioration in selectivity, by subtracting the adding an audio signal FM-detected through a BPF from and to a signal halving the amplitude of the audio signal FM-detected further through a BPF having the same characteristic. CONSTITUTION:An IF signal is inputted to the BPF22, a disturbing signal is eliminated and a transmission distortion D is generated. A modulation spectrum component at an output terminal of the BPF22 is expressed as S+D when S is a modulation signal. When the distortion of a detector 29 is small, the FM detection output becomes S+D also. This output is inputted to a non-inverting input of a subtractor 30. On the other hand, an output of the BPF22 inputted to an IF amplifier 23 is inputted to a BPF24 after amplification. When the characteristics of the BPFs 22, 24 are equal to those of the amplitude and phase, the output modulation spectrum component of the BPF24 is expressed approximately as S+2D. The output of the BPF24 is amplified and FM- detected, and the amplitude of S+2D is halved by an attenuator 27, 1/2S+D is inputted to an inverting input of the subtractor 30, where the signal is subtracted from the S+D at the non-inverting input, the 1/2S is outputted and a signal having no transmission distortion D is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission distortion improvement circuit for IF amplification, which improves distortion generated by a bandpass filter in an intermediate frequency amplification section of an FM receiver.

FIG. 1 is a block diagram showing the configuration of a tuner in a conventional FM receiver. In this Figure 1, 1 is a front end, a 2-digit IF filter, and a front end 1
The FM reception signal input to the front end 1 converts the FM signal into an intermediate frequency, and sends it to the IF filter 2, where the interfering signal is removed, and the signal is sent to the F amplifier 3. Amplify intermediate frequency signals. This IF
The intermediate frequency signal amplified by the amplifier 3 is converted to F by the FM detector 4.
M detection is performed to obtain a low frequency signal.

In this case, as the IF filter 2, a filter is used that places emphasis on amplitude characteristics and phase characteristics in order to satisfy both performance and low distortion characteristics when selected. For example, a SAW filter, a Bessel type LC filter, etc. are used.

FIG. 2 is a diagram showing an example of the configuration of a conventional T'M negative feedback tuner. In FIG. 15 is an FM detector, 16 is a low-pass filter (
The output of this low-pass filter 16 is fed back to the V6O13 ('pressure controlled oscillator) to form a loop. This V6O13 allows the frequency of the local oscillation circuit to be controlled by voltage.

In the case of this figure 2, the output of RF amplifier II is sent to mixer 12.
There, it is mixed with the output signal of V6O13 to extract an intermediate frequency signal, and this intermediate frequency signal is passed through an IF filter 13 and amplified by an IF amplifier 14, and then subjected to de-JVi detection by an FM detector 15 to generate a low frequency signal. Samurai, this low frequency No. 15 is used as a low pass filter J6, and FI ~ 1
The frame wave output is obtained from the output terminal f18i.

In the case of this FIG. 2, % shows the configuration of a tuner that performs F'M negative feedback, and since the loop is configured so that the output of the low-pass filter 16 is negative feedback to V6O13, At the output of mixer 12, the original F'
The frequency shift of the M signal becomes a compressed signal. This corresponds to isometrically widening the band of the IF filter 13, thereby improving distortion.

However, there is a limit to the performance improvement of the F filter 13.
In the case of FM negative feedback, the interference signal is also compressed at the same time, resulting in poor selectivity. Furthermore, depending on the amount of feedback, there is a risk of oscillation, and the wave number shift becomes smaller, resulting in a lower wave rate.

This invention was made in order to eliminate the drawbacks of the conventional F series, and in the intermediate frequency amplification stage of the B''M receiver, the transmission distortion generated by the selection element of the bandpass filter does not deteriorate the selectivity. It is an object of the present invention to provide a transmission distortion improvement circuit in IF' amplification that can eliminate the above distortion with a simple configuration.

Embodiments of the transmission distortion improvement circuit in IP amplification of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram showing the configuration of one implementation Vu. In this FIG. 3, it is an AH antenna. The FM signal received by antenna A is input to the front end 21.

The output end of the front end 21 is connected via a first bandpass filter 22 to each input end of an IF' amplifier 23,28. The output end of the IF amplifier 23 is connected to the input end of an IF amplifier 25 via a second bandpass filter 24, and the output end of this IF' amplifier 25 is connected to the input end of a second FM detector 26. has been done. The output end of the second FM detector 26 is connected to the first input end ((-) input end) of the subtracter 30 via an attenuator 27.

10,000, ±Ec21 F output terminal Vi of amplifier 28 first F
It is connected to the input end of the M detector 29, and this first F
The output terminal of the M detector 29 is connected to the second input terminal of the subtracter 30 ((
-H input terminal).

An FM detection output is obtained from the output terminal of this subtracter 30.

Next, the operation of the transmission distortion improvement circuit in F amplification of the present invention configured as above will be explained.

The FM signal received by antenna A is sent to front end 2.
1, and an IF' signal subjected to the same wave number conversion is obtained. This IF multiplied signal first band pass filter 22
The first bandpass filter 22 removes the interference M.sub.M. At this time, transmission distortion occurs.

Here, if the modulation signal is 81 and the transmission distortion is D, the modulation spectrum component at the output end of the first bandpass filter 22 can be expressed as (S+D). The output u of the first bandpass filter 22 with this modulated spectral component is sent to the IF amplifier 23.28.

The output of the first bandpass filter 22 amplified by the IF amplifier 28 (i.e., the IF multiplied signal is sent to the first FM detector 2
9, where it is subjected to FM processing. At this time, the first
If the frequency of the FM detector 29 is small (for example, pulse count detection is used), the output of the FMk wave will also be (
S 11)). The output of the first FM detector 29 is applied to the second input terminal ((g) input terminal) of the subtracter 30.

On the other hand, the output of the first bad-pass filter 22 inputted to the F amplifier 23 is inputted to the second band-pass filter 24 after being amplified there. If the second band-pass filter 24 has the same amplification phase, the #T, 2 band-pass filter 24 will cause the same distortion as the first band-pass filter 22. , the modulated spectrum components u and i'r at the output of the second bandpass filter 24 are generally 3(S+2D
).

After this newsletter is amplified by the IF amplifier 25, it is sent to the second FM
FM detection is performed by the detector 26, and the audio signal (S +2
D) is obtained. This second FM detector 26 also
Similar to the detector 29, one with low distortion characteristics is used. The audio signal (S+2
D) is transmitted to the attenuator 27.

In this attenuator 27, the audio signal (S +2
I) Reduce the amplitude of ) to 1/2. That is, (1/2
S + D), the first input terminal of the subtractor 30 (
(-) input terminal). The subtracter 30 subtracts the output (1/2S+D) of the attenuator 27 from the output (S10) of the first F'M horizontal t11 unit 29. As a result, a 1/2S audio signal is output from the output end of the subtracter 30, and a signal with transmission distortion canceled is obtained.

Note that if a delay device is provided before or after the first FM detector 29 to correct the delay time caused by the second bandpass filter 24, more complete distortion cancellation can be achieved.

Further, if the subtracter 30 and the attenuator 27 are, for example, an inverting amplifier with a gain of 1/2, then the subtracter 30 is used as an adder.

As described above, according to the transmission distortion improvement circuit in IF' amplification of the present invention, the IFiW signal obtained at the front end can be improved! After removing the interfering signal through the bandpass filter 81, the first FM detector performs FM detection to extract the audio signal, and the I11' signal passed through the first bandpass filter After passing through a second band pass filter having the same characteristics as the first band pass filter, the second FMM detector F゛ takes out the MM detected audio signal and takes the amplitude of this audio signal as a fraction. Since the audio signals input by the first and second detectors are subtracted or added, improvement can be achieved without using a bandpass filter.

Like FM negative feedback, there is no risk of oscillation due to feedback.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a tuner in a conventional FM receiver, and Fig. 2 is a block diagram showing an example of the configuration of a conventional FM negative feedback tuner. FIG. 2 is a block diagram showing the configuration of one embodiment of the logic circuit. 21... Front end 22... ml band pass filter 23.25
．． 28... IF amplifier 24... Second band pass filter 26... Second FM detector 27... Attenuator 29... First FM detector 30 --- Subtractor clock Applicant: Pioneer Corporation

Claims (1)

[Claims] a first bandpass filter that removes an interfering signal from the IP-multiplied signal obtained at the front end; and a first FM that performs FM detection on the output signal of the first bandpass filter to obtain a first audio signal. a detector, which has the same characteristics as the first band-pass filter and passes a predetermined frequency band of the output signal of the first band-pass filter;
) a second band-pass filter; a second FM detector that performs FM detection on the output signal of the second band-pass filter to obtain a second audio signal; means for reducing the amplitude of the second audio signal obtained by subtracting or adding the output signal of the means to the first audio signal No. 4g to obtain the first and second bandpass signals. Improving transmission distortion in IF amplifier circuits using a method for removing transmission distortion generated by filters (b)
Road.