JPS62139419A - Car radio circuit - Google Patents

Abstract

PURPOSE:To receive an FM sound signal for a TV always at a high SN ratio by switching a pass band and gain between an FM sound signal from an FM tuner part and an FM sound signal from a TV tuner part. CONSTITUTION:A ceramic filter switching circuit 5 switches the pass band and gain under control by a microcomputer 9. Since the SN ratio of a received FM sound signal is comparatively high and almost constant at the reception of an FM sound program, the pass band of a switching circuit 5 is set up to a wide value and the gain is improved to prevent the SN ratio from deterioration. At the reception of the FM sound signal for the TV, the pass band is narrowed to remove a noise component and the gain is reduced to prevent the noise component in the FM sound signal band from increase so that the SN ratio of the FM sound signal is improved and almost fixed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a car radio circuit capable of receiving FM audio programs and FM audio signals of television programs.

[Background of the invention]

In-vehicle radio receivers, that is, car radios, can receive not only FM audio programs but also FM TV programs.
It would be very convenient if it could also receive audio signals. In order to achieve this, K is a tuner unit for FM audio signals of television programs (hereinafter referred to as the TV tuner unit) and a
It would be possible to add a processing circuit to amplify and detect the intermediate frequency FM audio signal from the tuner section, but this is not desirable for car radios, which are large and bulky, and one of the requirements is to be compact. do not have.

Therefore, for example, in the technique disclosed in Japanese Patent Application Laid-open No. 59-181727, a tuning circuit is provided for each signal in order to enable selective reception of different types of signals. A processing circuit that processes output FM audio signals from a tuner unit for FM audio programs (hereinafter referred to as an FM tuner unit) and a TV tuner unit, based on a technology that uses a common processing circuit for the output signal of a tuning circuit. It is conceivable to make it common.

However, the car radio moves as the car moves, and the environment of its MB changes from moment to moment. For this,
FM audio signal radio waves of television programs with a high transmission frequency are affected by this environmental change to a greater extent than radio waves of FM audio programs, and the received electric field changes from moment to moment.

Therefore, simply by simplifying the circuit configuration by making the processing circuit for each FM audio signal common as described above, when receiving the FM9 audio signal of the television number, the resulting audio will be The sound fluctuates from moment to moment, making it extremely difficult to hear.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems, and to provide a car radio circuit that can make the car radio compact and can always receive FM audio signals of television programs at high s7g. .

[Summary of the invention]

In order to achieve this object, the present invention supplies an FM audio signal from an FM tuner section and an FM audio signal from a TV tuner section to a common processing circuit through means whose passband and gain are switchable. The present invention is characterized in that the passband and gain of the means are switched so that the S/N of each FM audio signal is optimized.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

The figure is a block diagram showing an embodiment of a car radio circuit according to the present invention, in which 1 is a TV tuner section, 2 is an antenna,
6 is a switching unit, 4 is an FM front end, 5 is a ceramic filter switching circuit, 6 is an amplification/detection circuit, 7 is a noise canceller, 8 is a decoder, 9 is a microcomputer, 10 is a grease scaler, 1] is a PLL (phase lock - loop) circuit, 12 is an LPF (low pass filter), 13 is a TV front end, 14 is a prescaler/PLL circuit, and 15 is an LPF.

In the figure, an antenna 2, a 1M front end 4,
Prescaler 1o, PLL circuit 1] and LPF
The FM tuner section consisting of z2, the processing circuit consisting of an amplification/detection circuit 6, a noise canceler 7, and a decoder 8, and a microcomputer (hereinafter referred to as microcomputer) 9 have the same configuration as a conventional car radio circuit. , and a switching section 3, a ceramic filter switching section 5, a TV front end 13, and a prescaler P.
A TV tuner section 1 consisting of an LL circuit 14 and an LPF 1s is added to enable reception of F-V audio signals of television programs.

Next, the operation of this embodiment will be explained.

First, when receiving an FM audio program or an AM audio program, by operating a predetermined operation button (not shown), the microcomputer 9 outputs a switching signal SF of a predetermined level, whereby the switching unit 3 is closed to the FM/AM side. . The received signal from the antenna 2 is sent to the 1M front end 4 via the switching unit 3.
is supplied to

On the other hand, according to the user's channel designation, the microcomputer 9 outputs N1 direct according to this channel, and thereby P
The frequency division ratio of the variable division circuit constituting the LL circuit 1 is set. Output signal f of local oscillator of 1M front end 4
is frequency-divided by a prescaler 10, further frequency-divided by the PLL circuit 1, and further frequency-divided by the above-mentioned variable frequency divider circuit, and the phase is compared with the reference signal from the Mototomi oscillator. The phase difference signal resulting from this is PLL
It is output from circuit l and passed through LPF12.

It is supplied to the 1M front end 4 as a tuning voltage VT. In the 1M front end 4, the output signal f of the local oscillator and the received signal are mixed, and this received signal becomes an intermediate frequency signal. Signal is 10.7MH
The output frequency of the local oscillator is set by the tuning voltage VT to be an intermediate homogeneous signal of z.

The intermediate frequency signal from the FM front edge 4 passes through a ceramic filter switching circuit 5 and is then sent to an amplification/detection circuit 6.
The signal is then amplified and detected. The output signal of the amplification/detection circuit 6 has noise components removed by a noise canceller 7, and then is supplied to a decoder 8, where a left channel signal R and a right channel signal R are generated and output.

When a predetermined channel of a television program is specified by the user, the microcomputer 9 outputs a switching signal sr of a different level from the above, thereby switching the switching section 3 to the TV side. The received signal from the antenna 2 is supplied to the TV front end 13 through the switching section 3.

Furthermore, the microcomputer 9
' value is sent to the prescaler/PLL circuit 14. As a result, the prescaler PL
The L circuit 14 and the LPF 15 output the FM audio signal of the designated channel from the TV front end 13 as a 10.7 MHz intermediate frequency signal. After passing through the ceramic filter switching circuit 5, this intermediate frequency signal is processed in the same manner as when receiving an audio program.

In this way, FM audio programs and television programs
By making the intermediate frequency of the audio signals the same as 10.7 MHz, these FM audio signals can be processed together by the processing circuits used in conventional car radio circuits. This makes it possible to simplify the circuit configuration.

By the way, as explained earlier, as the car moves, the SZN of the FM audio signal of the received television program increases.
changes. The ceramic filter switching circuit 5 is provided to prevent this.

The ceramic filter switching circuit 5 is configured so that the passband and gain can be switched.

When receiving an FM audio program, the SZN of the received FM audio signal is relatively high and almost constant, so the passband of the ceramic filter switching circuit 50 is set wide and the gain is set high to prevent deterioration of the SZN. To prevent.

On the other hand, when receiving an FM audio signal of a television program, the pass band is narrowed to remove the noise component, and the gain is lowered to prevent the noise component from increasing within the FM audio signal band. To improve the SZN of an audio signal so that it becomes almost constant.

Such switching of the ceramic filter switch circuit 5 is performed by a switching signal SW from the microcomputer 9. Ceramic filter switching circuit 5 having such a function
Although various configurations are possible, for example, it can be configured with a ceramic filter having each pass band as described above, an amplifier having each gain, and a changeover switch, and this changeover switch A predetermined ceramic filter and amplifier may be selected by controlling the switch signal SF using the switching signal SF. Another example of the ceramic filter switching circuit 5 is a ceramic filter whose pass band can be switched and an amplifier whose gain can be switched. It may be possible to switch.

Although the audio signal system of the AM audio program is omitted in the figure, the AM audio signal of this program is also received through the switching unit 3, and the tuning control voltage VT from the LPF 12 is applied to the front end 4 at F. Needless to say, the stations will be selected by.

〔Effect of the invention〕

As explained above, according to the present invention, the received FM audio signals of F and M audio programs and the received audio signals of television programs are converted into intermediate same wave number signals of the same wave number and selected. , these can be processed by the same processing circuit, simplifying the W5 printing process, and
Since the device is provided with a means for switching the passband and gain according to each received FM audio signal, an excellent effect can be obtained in that the S/N of each FM audio signal can always be set well.

[Brief explanation of drawings]

The figure is a block diagram showing one embodiment of a car radio circuit according to the present invention. 1...TV tuner section 3...Switching section 4...F
M front end 5...Ceramic filter switching circuit 6...
Amplification/detection circuit 8...Decoder 9...Microcomputer 13...TV front end

Claims (1)

[Claims] A car radio circuit that includes an FM tuner section that converts a received FM audio signal into an intermediate frequency signal of 10.7 MHz, and a processing circuit that amplifies and detects the intermediate frequency signal, and is configured to emit audio of a desired channel. In, F.M.
a first means for selecting between receiving an audio signal and receiving a television signal; and a second means for converting an FM audio signal in the received television signal into an intermediate frequency signal of 10.7 MHz.
means, and a third means whose passband and gain are switched between when receiving an FM audio signal and when receiving a television signal, and the third means includes the FM tuner section or the second means. A color radio circuit, characterized in that it supplies an FM audio signal of an intermediate frequency from the third means, and supplies an FM audio signal output from the third means to the processing circuit.