JPS6017952Y2 - FM tuner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tuner in an FM receiver in which a local oscillator and a detector are controlled by the oscillation of one crystal resonator.

Conventionally, the local oscillator is directly controlled by quartz, or the IF frequency is oscillated by a quartz oscillator, the W frequency by the received signal is compared with the IF frequency by quartz oscillation, and the condition is converted, and the local oscillator is generated using this distributed output. There are methods that control the frequency.

The above two methods control the frequency of each individual circuit section, but neither of them takes any measures regarding the stability, variation, etc. of the detector.

However, the frequency drift in an FM receiver is large, mainly in the local oscillator and detector.

Therefore, good stability in the receiver can only be achieved by simultaneously suppressing both the local oscillator and detector drifts.

An object of the present invention is to improve the stability of an FM receiver by controlling the drifts of the two circuits, namely, the local oscillator and the detector, with one quartz oscillator.

The present invention will be explained below based on the drawings.

As shown in FIG. 1, the FM tuner 1 of the present invention receives the output of a front end section 5 consisting of an antenna coupling/high frequency amplification circuit 2, a frequency conversion circuit 3, and a local oscillation circuit 4 through an intermediate frequency amplifier 6 and a mixer. 7 and a pulse count detector 9, a quartz oscillator 8 is provided in the mixer 7, and the output of the pulse count detector 9 is connected to a DC converter 10, and the DC output of the DC converter 10 is connected to the A to the local oscillator circuit 4 of the front end section 5
It is designed to be given as an FC signal.

Now, the front end section 5 selectively amplifies the desired radio waves,
Convert to an intermediate frequency that is easier to amplify.

The subsequent intermediate frequency amplifier 6 amplifies the intermediate frequency.

The quartz oscillator 8 generates a stable frequency using an oscillation circuit including a crystal resonator as a second oscillation means, and the mixer 7 mixes this frequency with the intermediate frequency from the intermediate frequency amplifier 6. The second intermediate frequency is converted to a second intermediate frequency lower than this intermediate frequency.

Since the frequency from the quartz oscillator as the reference frequency is extremely stable, compared to a specific oscillator, an intermediate frequency signal with less frequency fluctuation is supplied to the detector, improving drift, and since it detects at a lower frequency. , the modulation degree (deviation frequency/carrier frequency) is large, the detection efficiency is improved, and S
/N is improved.

Next, the pulse count detector 9 is composed of a limiter, a monostable multivibrator, etc., as is well known, and the output of the mixer 7 is supplied to the monostable multivibrator through the limiter, and the output of the mixer 7 is supplied to the monostable multivibrator through the limiter. Outputs a pulse train and performs pulse count detection.

The output of the pulse count detector 7 is demodulated through an audio circuit (not shown) including an integrator and is sent to a DC converter 10.

The DC converter 10 includes DC conversion means such as an integrator and a low-pass filter, and converts the detected output into a DC signal.

Here, the level of the DC signal corresponds to the deviation between the stable frequency of the quartz oscillator 8 and the intermediate frequency.

Next, the DC signal is fed back to the local oscillation circuit 4 as a first oscillation means, and functions to control the local oscillation frequency to the center frequency of the quartz oscillator 8.

Specifically, as the DC output of the FM detector detunes around the tuning point, positive and negative DC outputs are generated corresponding to the upper and lower frequencies of the center frequency, so the output is fed back to the local oscillation circuit, and the local oscillation circuit Positive tuning is maintained by providing it in the resonant circuit or controlling it in the actance circuit.

As shown in FIG. 2, the C converter 10 consists of a DC conversion circuit 11 such as an integrator low-pass filter, and a switching circuit 12 interposed between this and the front end section 5. 12 may be linearly tuned during tuning using, for example, the touch sensor 13, and after the tuning is completed, the feedback loop may be activated at the actual value.

In this invention, the quartz oscillator improves the stability of the pulse count detector, and at the same time, the amount of feedback as the output performs AFC control for the local oscillator, so the stability of the pulse count detector and oscillator is improved. It can be increased to the high precision of a single quartz oscillator.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an FM tuner according to the present invention, and FIG. 2 is a block diagram showing another embodiment. 1...-FM tuner, 4...Local oscillation circuit, 5...Front end section, 6...
・Intermediate frequency amplifier, 7...Mixer, 8...
...Quartz oscillator, 9...Pulse count detector, 10...DC converter, 11...
DC conversion circuit, 12... Song switching circuit, 13...
...Touch sensor.

Claims (2)

[Scope of utility model registration request] (1) In the FM receiver, a pulse count detector is provided as a detection means, and the frequency from the quartz oscillator and the intermediate frequency from the front end section are input to the mixer provided on the input side of the pulse count detector. The output of the pulse count detector is converted to DC by a DC converter, and the DC output is applied to a local oscillator in the front end section as an AFC signal.
tuner (2) The FM tuner according to claim 1, wherein the DC converter is composed of a DC conversion circuit, a switching circuit, and a switching circuit driven by a touch sensor.