JPS6345083Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a bandwidth switching circuit for an intermediate frequency amplification stage in an FM receiver.

(Prior art) Conventionally, as disclosed in Japanese Patent Publication No. 56-18035, an intermediate frequency amplification stage is equipped with a narrow band intermediate frequency amplifier and a wide band intermediate frequency amplifier, and one of them is selected by a changeover switch according to the receiving condition. At the same time, the oscillation frequency of the local oscillator is configured to be switchable by a changeover switch that operates in conjunction with the changeover switch, and the center frequency of the intermediate frequency signal from the mixer is always set to the intermediate frequency regardless of the changeover of the intermediate frequency amplifier by the changeover switch. The center frequency of the selectivity characteristic of the frequency amplification stage is matched to compensate for the center frequency deviation that exists between the selection element of the wideband intermediate frequency amplifier and the selection element of the narrowband intermediate frequency amplifier.
There is a bandwidth switching circuit for the intermediate frequency amplification stage in an FM receiver.

When using the above-mentioned conventional band switching circuit of the intermediate frequency amplification stage in the FM receiver, when the bandwidth of the center frequency stage is switched according to the reception condition, the oscillation frequency of the local oscillator is switched in conjunction with the band switching circuit of the intermediate frequency amplification stage in the FM receiver. Selection of the center frequency of the selectivity characteristics of the wideband intermediate frequency amplifier and the selection of the narrowband intermediate frequency amplifier, which is caused by a difference in characteristics between the selection element of the wideband intermediate frequency amplifier and the selection element of the narrowband intermediate frequency amplifier, etc. The deviation between the center frequency of the frequency characteristic is compensated for,
The center frequency of the intermediate frequency signal from the mixer is made to match the center frequency of the selectivity characteristic of the intermediate frequency amplification stage, thereby eliminating problems such as deviation of the minimum distortion point during signal reception.

However, when using the above-mentioned conventional bandwidth switching circuit of the intermediate frequency amplification stage in the FM receiver,
The disadvantage was that the indication on the FM receiver's tuning meter would shift by the amount that the intermediate frequency was shifted by switching the bandwidth of the intermediate frequency amplification stage.

(Purpose of the invention) The present invention has been made in view of the above, and it is an FM system that eliminates the above drawbacks and prevents the indication of the tuning meter from shifting even when switching the bandwidth of the intermediate frequency amplification stage. An object of the present invention is to provide a bandwidth switching circuit for an intermediate frequency amplification stage in a receiver.

The present invention will be explained below using examples.

(Structure of the invention) FIG. 1 is a block diagram showing an embodiment of the invention.

In one embodiment of the present invention, an antenna 1, a high frequency amplification stage 2, a local oscillator 3, a mixer 4, an intermediate frequency amplification stage 5, an FM demodulator 6, a low frequency amplification stage 7, a speaker 8 and a tuning meter 9 provide an FM The receiver is configured.

The intermediate frequency amplification stage 5 is a narrowband intermediate frequency amplifier 1
0, the outputs of the wideband intermediate frequency amplifier 11 and the narrowband intermediate frequency amplifier 10 and the wideband intermediate frequency amplifier 1
Selector switch 1 for selecting either one of the outputs of 1
2, and a narrow or wide band intermediate frequency amplifier 10 or 11 selected by a changeover switch 12.
The output of the FM demodulator 6 is supplied to the FM demodulator 6. The local oscillator 3 is constituted by a frequency synthesizer consisting of, for example, a PLL circuit, and the oscillation frequency of a reference frequency oscillator 13 of the frequency synthesizer is configured to be switchable by switching and connecting a capacitor 14 and a capacitor 15. Capacitor 14 and capacitor 15 are switch 1
The connection is configured to be switched by a changeover switch 16 that switches in conjunction with 2.

On the other hand, the tuning meter 9 is composed of a center zero indicator as is well known, is supplied with the output DC voltage of the FM demodulator 6, and is configured to display the tuning state by the S-shaped characteristic output of the FM demodulator 6. There is. Furthermore, potentiometers 17 and 18 are provided to divide the voltage +B, and the output voltage of potentiometer 17 and the output voltage of potentiometer 18 are switched by a changeover switch 19 that switches in conjunction with changeover switch 12. is selected and applied to the tuning meter 9 as a bias voltage.

(Function of the invention) In one embodiment of the invention configured as described above, when the radio wave conditions are good without interference etc., the distortion of the demodulated output signal is reduced by selecting the broadband intermediate frequency amplifier 11 with the changeover switch 12. Good sound quality can be obtained. Furthermore, when the radio wave conditions are poor due to interference, the narrowband intermediate frequency amplifier 10 is selected by the changeover switch 12, thereby eliminating the interference and making it possible to reliably receive the desired station.

Further, in conjunction with switching between narrowband intermediate frequency amplifier 10 and wideband intermediate frequency amplifier 11 by changeover switch 12, capacitor 14 and capacitor 15 of reference oscillation frequency oscillator 13 are switched, and the reference frequency oscillation frequency changes by a constant frequency. Therefore, the deviation between the center frequency of the selectivity characteristic of the narrowband intermediate frequency amplifier 10 and the center frequency of the selectivity characteristic of the wideband intermediate frequency amplifier 11 is compensated, and the intermediate frequency from the mixer 4 is transferred to the changeover switch 12. Therefore, the selectivity center frequency is changed to match both the selectivity center frequency of the narrowband intermediate frequency amplifier 10 and the selectivity center frequency of the wideband intermediate frequency amplifier 11.

Further, the voltage of the potentiometer 17 and the voltage of the potentiometer 18 are switched in conjunction with switching between the narrowband intermediate frequency amplifier 10 and the wideband intermediate frequency amplifier 11 by switching the changeover switch 12.
The bias voltage applied to the tuning meter 9 changes, and the indication of the tuning meter 9 is biased by a fixed value. So potentiometer 1
By setting the divided voltage of voltage +B by 7 and 18, tuning is performed in response to the shift in the center frequency of the intermediate frequency signal from the mixer 4 due to the change in the oscillation frequency of the local oscillator 3. The indicated value of the meter 9 is corrected.

(Effects of the invention) As explained above, according to the invention, when the bandwidth of the intermediate frequency amplification stage is switched to a narrow bandwidth or a wide bandwidth, the local oscillation frequency is varied by a fixed frequency, and the tuning meter Since it is configured to bias the frequency, it is possible to correct and match the deviation between the center frequency of the intermediate frequency from the mixer and the center frequency of the selectivity characteristic of the intermediate frequency amplification stage that occurs when switching the bandwidth. Inconveniences such as the deviation of the minimum distortion point are eliminated, and the deviation in the indication of the tuning meter due to the correction of the deviation can be corrected, and the display of the minimum distortion point does not deviate.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention. 1...Antenna, 2...High frequency amplification stage, 3...
Local oscillator, 4...Mixer, 5...Intermediate frequency amplification stage, 6...FM demodulator, 7...Low frequency amplification stage, 8
...Speaker, 9 ...Tuning meter, 10
... Narrowband intermediate frequency amplifier, 11 ... Wideband intermediate frequency amplifier, 12, 16 and 19 ... Changeover switch, 13 ... Reference frequency oscillator, 14 and 1
5... Capacitor, 17 and 18... Potentiometer.

Claims (1)

[Scope of utility model registration request] A switching means for switching the bandwidth of the intermediate frequency amplification stage to a wide bandwidth or a narrow bandwidth, and means for varying the oscillation frequency of the local oscillator in conjunction with the switching means, regardless of the switching by the switching means. The center frequency of the intermediate frequency signal from the mixer is always made to match the center frequency of the selectivity characteristic of the intermediate frequency amplification stage, and the shift in the center frequency of the intermediate frequency amplification stage between wide bandwidth and narrow bandwidth is compensated for. A bandwidth switching circuit of an intermediate frequency amplification stage in an FM receiving device according to the present invention, further comprising means for biasing the indication of a tuning meter by a value corresponding to the deviation of the center frequency in conjunction with the switching means. Bandwidth switching circuit for intermediate frequency amplification stage in FM receiver.