JPH03155221A - Fm receiver - Google Patents

Abstract

PURPOSE:To suppress inter-station noise during channel channel selection operation by controlling a gain of an FM demodulator in response to a current of a current source and decreasing the gain of the FM demodulator when an FM signal input is small and when channel selection is in inter-stations so as to avoid noise at the output. CONSTITUTION:An intermediate frequency signal applied to an input terminal 6 is amplified by a 1st intermediate frequency amplifier 1 and further amplified by a 2nd intermediate frequency amplifier 2, the amplitude is limited, the signal is demodulated into an audio signal by an FM demodulator 3 and outputted to an output terminal 7. On the other hand, the signal inputted to a detector 4 from the output of the 1st intermediate frequency amplifier 1 is detected and the intensity of the input signal is detected and its detected signal is fed to a current source 5 and the current in response to the detected signal is fed to the Fm demodulator 3 and the gain of the FM demodulator 3 is controlled with the supplied current. Consequently, when the intensity of the input signal is week, the gain of the FM demodulator 3 is decreased, thereby preventing noise from appearing at the output terminal 7.

Description

[Detailed description of the invention] Industrial application field The present invention is a frequency modulated wave receiver (hereinafter referred to as an FM receiver).
This is related to the configuration of the .

Conventional technology In recent years, FM receivers have weak input electric field strength, and conventional FM
When the input signal level is such that the amplitude limiting operation of the intermediate frequency amplification stage included in the receiver is not performed sufficiently, or between stations during channel selection, a large noise component is output to the FM demodulation output terminal, and this is transmitted to the subsequent stage. When amplified and listened to through speakers, it was noticeably harsh.

A conventional FM receiver will be explained below.

FIG. 2 shows a block diagram of a conventional FM receiver. In FIG. 2, 1 is an intermediate frequency amplifier;
3 is an FM demodulator, 6 is an input terminal, and 7 is an output terminal.

The operation of the FM receiver configured as described above will be described below.

First, a frequency modulation signal converted to an intermediate frequency applied to an input terminal 6 is amplified and limited in amplitude by an intermediate frequency amplifier 1, demodulated into an audio signal by an FM demodulator 3, and outputted to an output terminal 5.

FIG. 3 shows the relationship between the input signal level and the signal output and noise output after FM demodulation. What is shown by the broken line is the characteristic of the circuit according to the conventional example.

Problems to be Solved by the Invention However, in the conventional configuration described above, the noise output is the sum of noise components included within the demodulation band of the FM demodulator, as shown in FIG. When the level of the input signal shown in FIG. 3 falls below the level at which the amplitude limiting operation of the intermediate frequency amplifier 1 begins to operate, the amplitude limiting function of the intermediate frequency amplifier 1 does not operate sufficiently, and the noise level increases, resulting in a signal-to-noise ratio. It is normal that it is bad. Furthermore, since the noise level itself is high, amplifying the sound and listening to it through a speaker is extremely unpleasant to the ears.

The present invention solves the above-mentioned problem of the conventional inter-station setting, and aims to improve the absolute level of noise during weak input, and also suppresses the inter-station noise during channel selection, thereby providing a good FM signal to the ears.
The purpose is to provide a receiver.

Means for Solving the Problems To achieve this object, the FM receiver of the present invention
a first intermediate frequency amplifier that amplifies an intermediate frequency;
a detector that detects the output of the intermediate frequency amplifier and generates a detection signal corresponding to the input electric field strength; a current source that responds to the detection signal; and a second detector that further amplifies the output of the first intermediate frequency amplifier. The device includes an intermediate frequency amplifier and an FM demodulator that demodulates the output signal of the second intermediate frequency amplifier, and has a configuration in which the gain of the FM demodulator is controlled according to the current value of the current source.

Effect: With this configuration, it is possible to obtain an FM receiver that reduces the gain of the FM demodulator when the FM signal input is small and between stations during the channel selection operation to prevent noise from occurring in the output.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of an FM receiver in an embodiment of the present invention. In Figure 1, 1,
2 is an intermediate frequency amplifier that amplifies the intermediate frequency; 3 is an FM demodulator that demodulates the output of the intermediate frequency amplifier 2; and 4 is a detector that detects the output of the intermediate frequency amplifier 1 and generates a detection signal corresponding to the input electric field strength. 5 is a current source that provides a current in response to a detection signal, 6 is an input terminal, and 7 is an output terminal.

The operation of the FM receiver configured as described above will be described below.

First, the intermediate frequency signal applied to the input terminal 6 is amplified by the first intermediate frequency amplifier 1, further amplified and amplitude limited by the second intermediate frequency amplifier, and demodulated into an audio signal by the FM demodulator 3. It is output to the output terminal 7. -Auspicious 1
The signal input to the detector 3 from the output of the intermediate amplifier is detected and the intensity of the input signal is detected.The detection signal is sent to the current source 5, and the current corresponding to the detection signal is sent to the FM demodulator 3. The gain of the FM demodulator is controlled by the supplied current. As a result, when the input signal strength is weak, the gain of the FM demodulator 3 is lowered to prevent noise from appearing at the output terminal 7.

The solid line in FIG. 3 shows the relationship between the input signal level and the signal output and noise output after FM demodulation according to the embodiment. As you can see from the figure, the noise level during weak input is reduced.

As described above, according to this embodiment, there is a first intermediate frequency amplifier that amplifies the FM intermediate frequency, and a detector that detects the output of the first intermediate frequency amplifier and generates a detection signal corresponding to the input electric field strength. and a current source responsive to the detection signal, a second intermediate frequency amplifier that further amplifies the output of the first intermediate frequency amplifier, and an FM demodulator that demodulates the output signal of the second intermediate frequency amplifier. The purpose is to improve the absolute level of noise during weak input by controlling the gain of the FM demodulator according to the current value of the current source, and also to suppress inter-station noise during channel selection operation. Good FM to the ear with
A receiver can be provided.

Now, one embodiment of the present invention will be explained in more detail with reference to FIG. The FM intermediate frequency signal applied to the input terminal 6 is amplified by a first intermediate frequency amplifier l composed of a differential amplifier of transistors 102 and 103 and transistors 106 and 107, and is taken out from a load 108 and 109. It is amplified by a second intermediate frequency amplifier composed of a differential amplifier of transistors 112 and 113, and taken out from a load 114 and 115.
8,130,131.132, the phase is changed with respect to the frequency of the FM intermediate frequency signal, and the transistor 1
It enters one of the multipliers consisting of 19, 120, 124°125. The other signal taken out from the loads 114 and 115 is amplified by a differential amplifier of transistors 123 and 126, and enters the other multiplier, and a demodulated signal of the FM intermediate frequency signal is obtained at the collector of the transistor 120, that is, the output terminal 7. It will be done. The magnitude of this demodulated signal is determined by the current source 156
and the gain determined by the values of the loads 121 and 122. However, it is assumed that the collector current of the transistor 146 is not flowing.

Now, the FM intermediate frequency signal taken out from the load 109 is applied to the second intermediate frequency amplifier and the coupling capacitor 1
After being applied to the detector 4 through 37 and detected, the signal is input as a detection signal to a comparator consisting of transistors 146 and 147.

First, when the input signal strength is high enough, the detection signal is high (the transistor 146 is non-conductive and the gain of the FM demodulator is maximum.

Then, when the input signal strength is low, the detection signal is low, transistor 146 conducts, and the current in transistor 156 is constant, so the FM demodulator current decreases and the gain decreases. Therefore, the output signal level at the output terminal is small.

As described above, by using a current source that responds to the input signal strength, F
By controlling the gain of the M demodulator, the absolute level of noise can be improved at weak inputs.

Effects of the Invention As described above, the present invention includes a first intermediate frequency amplifier that amplifies an FM intermediate frequency, and a detector that detects the output of the first intermediate frequency amplifier and generates a detection signal corresponding to the input electric field strength. , a current source responsive to the detection signal, a second intermediate frequency amplifier that further amplifies the output of the first intermediate frequency amplifier, and an FM demodulator that demodulates the output signal of the second intermediate frequency amplifier. FM according to the current value of the current source.
By controlling the gain of the demodulator, the absolute level of noise is reduced during weak input, and it also suppresses inter-station noise during channel selection, resulting in excellent FM reception that improves the listening experience. This is something that can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an FM receiver according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional FM receiver. FIG. 3 is a diagram showing the limiter characteristics of the FM receiver of FIGS. 1 and 2, in which the vertical axis represents the demodulated signal output voltage and the demodulated noise output voltage, and the horizontal axis represents the input signal voltage. FIG. 4 is a circuit diagram showing a specific example of one embodiment of the present invention. 1.2...Intermediate frequency amplifier, 3...F
M demodulator, 4...detector, 5...current source, 6...input terminal, 7...output terminal. Figure 1 Figure 2 Figure 3 Enter @Bell Vxy (jBμ)

Claims (1)

[Claims] a first intermediate frequency amplifier that amplifies an FM intermediate frequency; a detector that detects the output of the first intermediate frequency amplifier and generates a detection signal corresponding to the input electric field strength; and a current source that responds to the detection signal. , a second intermediate frequency amplifier that further amplifies the output of the first intermediate frequency amplifier, and an FM demodulator that demodulates the output signal of the second intermediate frequency amplifier, and according to the current value of the current source. An FM receiver characterized in that the gain of an FM demodulator is controlled by