JPS6143319Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a tuning circuit for a tuner, and particularly to a tuning circuit using a variable capacitance diode as a tuning element.

In recent tuners, electronic tuning circuits that use variable capacitance diodes instead of variable capacitors (variable capacitors) are often used.
All such electronic tuning circuits can be electrically controlled, and therefore have the advantage that the circuit can be constructed in a compact size.

The capacitance of a variable capacitance diode changes depending on the DC voltage applied to both ends, and the tuning capacitance of the variable capacitance diode when receiving a desired broadcasting station depends on the DC voltage applied according to the tuning operation. It is determined accordingly. A received signal is input while this predetermined DC voltage is applied to the variable capacitance diode, and especially when the signal level of this received signal is relatively large, it is not applied to the variable capacitance diode due to the characteristics of the variable capacitance diode itself. This results in an apparent increase in the DC voltage. In other words, the variable capacitance diode is used with a reverse bias V _R applied, but the forward voltage of the variable capacitance diode is
When the peak _value of the input voltage e approaches or exceeds V _R +V _F , a part of the positive side peak value is rectified and superimposed on V _R due to general diode characteristics, and apparently, This means that the tuning voltage has increased. Therefore, since the tuning capacitance of the variable capacitance diode changes depending on the signal level, the tuning frequency shifts and reception becomes impossible, which is undesirable.

Therefore, an object of the present invention is to provide a tuning circuit that can always obtain a stable reception state without being affected by the signal level of a received signal.

The tuning circuit according to the present invention is intended for an electronic tuning circuit using a variable capacitance diode as a tuning element, and is characterized by controlling the DC voltage applied to the variable capacitance diode according to the signal level of a received signal. It is said that

Hereinafter, the present invention will be explained in detail with reference to the drawings.

The figure is a circuit block diagram of an embodiment of the present invention. In the figure, an RF amplifier 1 including a coil L and a variable capacitance diode VC selects a desired broadcast station from among broadcast waves received by an antenna 2, amplifies it, and supplies it to a mixer 3. The high frequency reception signal supplied to the mixer 3 is mixed with the local oscillation signal from the local oscillation circuit 4, converted into an intermediate frequency (IF) signal, and then supplied to the next stage IF amplifier (not shown).

The received signal from the RF amplifier contains a direct current component as a tuning voltage applied to the variable capacitance diode VC and a signal component, and is supplied to the mixer 3, which is used to detect the signal level of this received signal. It is supplied to a capacitor C constituting the detection means 5, and the DC component is blocked. The received signal, in which the DC component has been cut off and only the signal component remains, is subjected to half-wave rectification by the diode D, and then converted and outputted by the low-pass filter 6, for example, into a DC voltage corresponding to the carrier wave signal level of the broadcast wave. This carrier wave signal level changes depending on the distance from the broadcasting station, the conditions of the receiving location, the antenna, etc.

The output voltage of low pass filter 6 is RF amplifier 1
The voltage is supplied to a control means 7 for controlling the tuning voltage to be applied to the variable capacitance diode VC, and after being phase inverted and amplified by a phase inverter 8, it is applied to a tuning voltage control circuit 9. A tuning voltage control circuit 9 controls the tuning voltage according to the output voltage of the phase inverter 8. That is, for example, when the signal level of the received signal is relatively large, the tuning applied in response to the tuning operation is applied to cancel out the DC component that attempts to change the tuning capacitance of the variable capacitance diode VC according to the signal level. RF amplifier 1 by correcting the voltage
supply to. It goes without saying that the control means 7 may have a configuration in which the output voltage of the low-pass filter 6 is directly used as the control voltage of the tuning voltage control circuit 9 without using the phase inverter 8. Further, the level detection means is not limited to the circuit configuration of the above embodiment, and various modifications can be made.

As detailed above, according to the present invention, even if the signal level of the received signal changes, the tuning capacitance of the variable capacitance diode can be reliably maintained at a value corresponding to the desired receiving station, without causing tuning deviation. A stable reception condition is always obtained.

[Brief explanation of the drawing]

The figure is a circuit block diagram of an embodiment of the present invention. Explanation of symbols of main parts, 1...RF amplifier, 5
...Level detection means, 6...Low pass filter,
7... Control means, 9... Tuning voltage control circuit, VC
...variable capacitance diode.

Claims (1)

[Scope of utility model registration request] The tuning circuit uses a variable capacitance diode as a tuning element, and includes a level detection means for detecting a carrier wave signal level of a received broadcast wave and outputting a detection signal according to the level, and a level detection means for detecting a carrier signal level of a received broadcast wave and outputting a detection signal according to the level, and a A tuning circuit comprising: control means for controlling a tuning voltage applied to the variable capacitance diode, and correcting a capacitance deviation of the variable capacitance diode in response to an excessive input to the tuning circuit.