JPS5936029Y2 - AFC control circuit - Google Patents

Description

[Detailed explanation of the invention] This invention is based on the AF
This invention relates to an AFC control circuit that uses a plurality of sensors and uses the difference in output as a new control output in order to reduce malfunctions of the C control circuit.

A conventional AFC control circuit is shown in FIG.

Reference numeral 1 in FIG. 1 is a sensor that operates this AFC control circuit, and is a tuning knob or equivalent.

2 is a panel board through which signals are sent to the amplifier circuit.

The amplifying circuit is mainly composed of an amplifying transistor 3, and a voltage of 10 B is applied to the drain of the amplifying transistor 3 via a load resistor 4.

The gate of the amplifying transistor 3 is grounded via a bias resistor 5, and the source is grounded via a bias resistor 6 and a bypass capacitor 7.

The drain of the amplifying transistor 3 is grounded via a coupling capacitor 8 and a resistor 9, and the connection point between the coupling capacitor 8 and the resistor 9 is connected via a diode 10 to the gate of a transistor 13.

Diode 10 is for rectification, and its cathode is connected to resistor 1
2 and a smoothing capacitor 11 in a parallel circuit.

The resistor 12 is a resistor for determining a discharge time constant, and the smoothing capacitor 11 is for smoothing the signal rectified by the diode 10.

Further, the reference voltage SV is applied to the drain of the transistor 13, and the source is connected to the AFC input terminal 14 via a limiting resistor 16 and to the AFC output terminal.

The AFC input terminal 14 is connected to an AFC voltage terminal of an FM detector or the like, and the AFC output terminal 15 is connected to an AFC input terminal of a local oscillation circuit such as a tuner.

In FIG. 1, the voltage induced in the sensor 1 increases when a part of the human body (such as a finger) comes into contact with it.

This voltage is amplified by the amplifying transistor 3, and this amplified signal is obtained across the resistor 9 via the coupling capacitor 8.

The voltage across this resistor 9 is rectified by a diode 10 and smoothed by a smoothing capacitor 11.

The DC voltage obtained across the smoothing capacitor 11 is applied to the gate of the transistor 13, and becomes a control voltage for switching the transistor 13.

Now, as the voltage across the smoothing capacitor 11 increases, conduction occurs between the drain and source of the transistor 13, and the reference voltage Sv from the reference power supply connected to the drain of the transistor 13 is obtained at the AFC terminal 15.

Therefore, when the sensor 1 is a tuning knob, when a tuning operation is performed, the AFC voltage becomes a constant value of the reference voltage S■, and the tuning operation can be performed accurately.

In such a conventional AFC control circuit, sensor 1 is
As the sensitivity is increased, the transistor 13 becomes conductive due to the noise induced in the sensor 1. This makes it difficult to set the optimum sensitivity, and also depends on the environmental conditions of the device using this sensor. There is a drawback that the change may cause malfunctions such as the transistor 13 becoming conductive or not conductive.

This idea was made to eliminate the above-mentioned drawbacks of the conventional AFC. By arranging multiple sensors and finding the difference in voltage induced between them, it is possible to increase sensitivity and reduce malfunctions. The purpose is to provide a control circuit.

Embodiments of the AFC control circuit of this invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram of one embodiment.

In this Fig. 2, in order to avoid duplication, the same parts as in Fig. 1 are given the same reference numerals and their explanations are omitted, and the parts different from Fig. 1 are emphasized. state

That is, in FIG. 2, a sensor 1, a panel 2, an amplifying transistor 3, a load resistor 4, bias resistors 6, 7,
Bypass capacitor 7, coupling capacitor 8, resistor 9, diode 10, smoothing capacitor 11. Resistor 12, transistor 13, AFC input terminal 14, AFC output terminal 15
, and the limiting resistor 16 are exactly the same as those shown in FIG. 1, except for the points described below.

That is, the second sensor 1A is provided close to the sensor 1.

Sensor 1 and IA are installed insulated.

The voltage induced in the sensor 1 is applied to the gate of the amplification transistor 3 in the same manner as in FIG. 1, but the voltage induced in the sensor 1A is applied to the gate of the amplification transistor 17.

The connection relationship from the amplification transistor 17 to the gate of the transistor 13 is exactly the same as the connection relationship from the amplification transistor 3 to the gate of the transistor 13.

The gate of the amplifying transistor 17 is grounded via a bias resistor 19, and the source is grounded via a bias resistor 20 and a bypass capacitor 21.

A voltage of 10 B is applied to the drain via a load resistor 18.

This drain is grounded via a coupling capacitor 22 and a resistor 23.

A connection point between the coupling capacitor 22 and the resistor 23 is grounded via a diode 24, a parallel circuit of a resistor 26, and a smoothing capacitor 25.

The resistor 26 is a discharge resistor for determining a time constant.

The smoothing capacitor 25 is for smoothing the DC voltage rectified by the diode 24.

The anode of the diode 24 is connected to the gate of the transistor 13 via a resistor 28, and the anode of the diode 10
The cathode of is connected to the gate of the transistor 13 via a resistor 27.

Note that the diodes 10 and 24 have opposite polarities, and the DC voltage obtained across the smoothing capacitor 25 through the diode 24 has the opposite polarity to the DC voltage obtained across the smoothing capacitor 110.

Next, the operation of the AFC control circuit of this invention constructed as described above will be explained.

The system of sensor 1 is the same as that in Fig. 1, and
The noise component of the voltage induced in the sensor 1A can be considered to be equivalent to that induced in the sensor 1.

A signal amplified by the amplification transistor 17 is obtained across the resistor 23 through the coupling capacitor 22.

The voltage amplified by the amplifying transistor 17 passes through the coupling capacitor 22 and is rectified by the diode 24, so that a smoothed DC voltage is obtained across the smoothing capacitor 25.

This DC voltage has a polarity opposite to that available across the smoothing capacitor 11.

The voltage across the smoothing capacitor 11.25 is the voltage across the resistors 27 and 2.
8 and applied to the gate of transistor 13.

Therefore, by determining the resistance ratio of the resistors 27 and 28 so that the transistor 13 does not conduct when the sensor 1 is not in contact with the human body, malfunctions due to noise can be reduced.

If a part of the human body comes into contact with sensor 1, sensor 1A
Since it is insulated from sensor 1, the induced voltage is larger in sensor 1 than in sensor 1A.

Therefore, smoothing capacitor 1 is smaller than smoothing capacitor 25.
The DC voltage obtained across the transistor 1 increases, and a positive voltage is applied to the gate of the transistor 13, causing the transistor 13 to conduct and perform the same operation as the conventional one.

This makes it possible to reduce malfunctions and further increase sensitivity.

FIG. 3 shows only the sensor part in another embodiment of this invention, and as shown in FIG. 2, the sensors 1 and 1A are not provided separately, and the panel board 2 is used as the sensor. This is what was used.

It is clear that the operation in this case is similar to that in FIG.

As described above, according to the AFC control circuit of this invention, since a pair of sensors are provided and the difference in voltage induced in each sensor is determined and used as a control output, sensitivity can be increased and This has the effect of eliminating malfunctions even due to changes in environmental conditions.

[Brief explanation of drawings]

Figure 1 is a wiring diagram showing a conventional AFC control circuit, Figure 2 is a wiring diagram showing one embodiment of the AFC control circuit of this invention, and Figure 3 is a sensor in another embodiment of the AFC control circuit of this invention. FIG. 1.1A...sensor, 2...hanel,
3,17...Amplification transistor, 10.24
...Diode, 11゜25...Smoothing capacitor, 13...Transistor, 14.
...AFC input terminal, 15...AFC output terminal. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (3)

[Scope of utility model registration request] (1) A pair of sensors that each induce a voltage and whose induced voltage increases when a part of the human body comes into contact with it, a rectifier that obtains rectified voltages with different polarities from the induced voltage of each sensor, and this rectifier. An AFC circuit comprising a circuit that becomes conductive and outputs a predetermined reference voltage when a voltage deviation exceeds a predetermined value. (2) The AFC control circuit according to claim 1, wherein the sensors are insulated from each other. (3) The AFC control circuit according to claim 1, wherein one of the sensors is a panel.