JPS58117717A - Electronic type am tuner - Google Patents

Abstract

PURPOSE:To minimize the adverse effect due to harmonics from a limiter amplifier, by activating the limiter amplifier only at the automatic channel selection. CONSTITUTION:A control signal generating circuit 18 generates a control signal at the automatic channel selection only and turns on a switch means 6. As a result, an IF signal is supplied to the limiter amplifier only at the automatic channel selection. Thus, the limiter amplifier 7 is made active only at the automatic channel selection. Further, the circuit 18 is used in common with an AFC control circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic AM tuner, and more particularly to a voltage synthesizer one-way AM tuner.

The tuner has an added function of performing automatic tuning by sequentially changing the tuning frequency of the tuning circuit of the high frequency circuit section and the local oscillation frequency of the local oscillator circuit to perform a so-called up or down search operation. That is, a reversible counter capable of up and down counting is provided, and a clock pulse signal of a constant frequency is sent to the reversible counter until a synchronization detection signal is generated in response to an up or down command.
The counting output of this reversible counter is converted into, for example, D/A (digital/analog) to obtain a tuning voltage, and the tuning frequency and local oscillation frequency are controlled by this tuning voltage.

In the AM tuner, a limiter amplifier is provided for inputting the IP multiplied signal at the intermediate frequency (IP) stage.
A so-called S-curve characteristic is obtained by means of converting a change in the output frequency of the limiter amplifier into a voltage, and the automatic tuning operation is stopped by generating the tuning detection signal at the zero point of this S-curve. The signal system that generates the tuning detection signal, including the limiter amplifier, was activated not only during automatic tuning, but also during manual tuning and in a stationary state after tuning was completed. Therefore, there is a drawback that harmonics of the IF are generated due to the non-linearity of the limiter amplifier, which are fed back to the antenna and cause deterioration of the whistle sound characteristics.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electronic AM cheese that minimizes the adverse effects of harmonic components from a limiter amplifier.

The electronic AM tuner according to the present invention is configured to activate the limiter amplifier only during automatic channel selection.

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

The figure is a block diagram showing an embodiment of the present invention. The signal is received by an antenna 1, passed through an RF (high frequency) section 2, and mixed with a local frequency from a local oscillator circuit 4 in an RF signal mixer 3. The signal is converted twice.

The IP-multiplied signal is converted into an audio signal in the AM detection circuit 5 and is supplied to the limiter amplifier 7 via the switch means 6. The IP multiplied signal whose amplitude is limited by the limiter amplifier 7 is input to the S curve detection circuit 8 . The S-curve detection circuit 8 operates to convert a change in the IF multiplied signal frequency into a voltage, and its output voltage exhibits a so-called S-curve characteristic. The tuning detection circuit 9 generates a tuning detection signal at the zero point of the S curve based on the output of the S curve detection circuit 8.

This tuning detection signal becomes a stop signal that stops the automatic tuning operation described below.

Reference numerals 10 and 11 are switches for commanding up and down searches during channel selection, and output signals of these switches are applied to an auto-tuning input latch circuit 12 and a manual input gate circuit 13, respectively.

The auto-tuning input latch circuit 12 and the manual input gate circuit 13 are also input with manual/auto command signals having mutually opposite logics, which are generated by a mode switch (not shown) that selects between manual and automatic channel selection operations, for example. . The manual tuning control circuit 14 sends out clock pulses from the tuning clock output circuit 15 in response to the output of the manual input gate circuit 13, which is generated while the up or down switch is pressed during manual tuning.
This is the clock input of a reversible counter (not shown) in the controller 16. At this time, the reversible counter is controlled to count up or down in response to the up or down command, and the DC voltage corresponding to the counting content of this counter becomes a tuning voltage and is applied to the RF section 2 and the local oscillator circuit 4. Controls the tuning frequency and local oscillation frequency.

During auto tuning, the auto tuning input latch circuit 12 is activated and stores the suppressed state of the up or down switch, and controls the auto tuning control circuit 17 in accordance with the up or down command. This control circuit 17 performs an auto-tuning operation by sending clock pulses from the tuning clock output circuit 15 to the controller 16 in response to the output of the auto-tuning control circuit 17, and receives the tuning detection signal from the tuning detection circuit 9 mentioned above. By applying this, the sending of clock pulses to the controller 16 is stopped, thereby stopping the auto-tuning operation.

The above configuration is the same as that of a conventional AM tuner except that the switch means 6 is provided, and since it is well known, the details thereof will be omitted.

In the present invention, in addition to the above configuration, a control signal generation circuit 18 is provided which generates a control signal for controlling on/off of the switch means 6.
generates a control signal only during automatic channel selection and switches the switch means 6.
Turn on. As a result, since the TF multiplied signal is supplied to the limiter amplifier 7 only during automatic tuning, the limiter amplifier 7 is activated (operated) only during automatic tuning.

Electronic tuners use an AFO (automatic frequency) circuit (not shown) that automatically controls the frequency of the local oscillator circuit 4 so that it oscillates stably. need to be stopped.

For this reason, auto tuning input launch circuit 1
An AFO control circuit (not shown) is provided which generates an output based on each output of the 2 and manual input gate 13 only during automatic tuning to stop the operation of the AFO circuit. It can also be used as the generating circuit 18.

It should be noted that the present invention is not limited to the above-described configuration; in short, any configuration may be used as long as the limiter amplifier 7 is activated only during automatic channel selection.

As detailed above, in the present invention, since the limiter amplifier is activated only during automatic channel selection, it is possible to minimize adverse effects such as deterioration of whistle sound characteristics due to harmonic components from the limiter amplifier. I can do it.

[Brief explanation of the drawing]

The figure is a block diagram showing an embodiment of an electronic AM tuner according to the present invention. Explanation of symbols of main parts 3...Mixer 4...Local oscillator circuit 6...
Switch means 7...Limiter amplifier 8...S
Curve detection circuit 15...Tuning clock output circuit 16...Controller 18...Control signal generation circuit Applicant
Pioneer Corporation

Claims (1)

[Claims] An electronic AM tuner comprising a limiter circuit inputting an intermediate frequency signal and configured to stop automatic tuning operation based on the output of the limiter circuit, the limiter circuit being activated only during automatic tuning. An electronic individual tuner characterized by being designed to