JPS6134770Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a strength meter drive circuit for an FM receiver.

Traditional FM receiver strength meter is FM
There was a drawback that the strength meter pointer would swing even when there was no broadcast signal. below,
A conventional strength meter drive circuit will be explained based on FIG.

In the figure, 1 is a limiter circuit and 2 is a detector. The strength meter drive circuit inputs the output from the limiter circuit 1 to the Peter detectors A ₁ , A ₂ to A _o , converts it into a DC component, and inputs it to a current mirror circuit consisting of a diode 9 and a transistor 10.
The voltage across the terminals of the resistor 12 causes the transistor 11 to
A bias is given to drive the strength meter 13.

Peak detector _A1 has transistors 6, 7, 8,
Consists of resistors 3, 5, and capacitor 4, converts the signal strength of FM broadcast waves into DC voltage,
It also has the function of converting it into electric current. Further, the peak detectors A ₁ , A ₂ to _{A o} are configured with the same circuit. Note that the diode 9 and the transistors 10 and 1
The circuit section including the resistor 1 and the resistor 12 is a drive circuit of the strength meter.

Generally, in order to drive the pointer of a strength meter smoothly, a bias voltage is applied from terminal 15 to each peak detector A ₁ , A ₂ to A _o , and the diode characteristics between the emitter and base of transistor 11 are applied to transistors 7 and 8. A small current is passed in order to eliminate the distortion of the strength meter. Therefore, even when there is no signal, a current is passed from the current mirror circuit consisting of the transistor 10 and the diode 9, and a potential is generated between the terminals of the resistor 12, which causes the strength meter to It has the disadvantage of causing 13 pointers to wave. Furthermore, the noise of the limiter circuit 1 itself is also amplified, resulting in the user having to grip the pointer even more, resulting in a feeling of discomfort.

The present invention solves the above-mentioned drawbacks, and provides an FM receiver suitable for IC implementation that does not cause the strength meter pointer to swing due to no broadcast signal or noise generated from the limiter circuit. The purpose of the present invention is to provide a strength meter driving circuit.

An embodiment of the strength meter drive circuit of the FM receiver according to the present invention will be described below with reference to FIG.

In FIG. 2, 1 is a limiter circuit, 2 is a detector, and the strength meter drive circuit is roughly divided into peak detectors B ₁ , B ₂ -B _o and a drive circuit C. Normally, the limiter circuit 1 is composed of several stages of differential amplifiers, and peak detectors B ₁ , B ₂ to B _o are constructed depending on the number of stages. The output currents of the peak detectors B ₁ , B ₂ -B _o are summed to drive the strength meter 33 via the drive circuit C.

The peak detector _B1 consists of a level detector.
The level detection circuit includes a transistor 18 and a resistor 20,
21, a resistor 21 is connected to the collector of the transistor 18, the other end is connected to the power supply voltage _Vcc , and the transistor 1
A resistor 20 is connected to the emitter of the transistor 18, and the other end is grounded, a transistor 19 is connected to the collector of the transistor 18, a capacitor 17 is connected to the emitter, and the other end is grounded. The comparator includes a differential pair consisting of transistors 22 and 23 and a multi-collector transistor 26 with one collector connected to its base, and a differential pair consisting of transistors 22 and 23, with the base of the multi-collector transistor 26 connected to the collector of the transistor 23. and multi-collector transistor 2
6 is connected to the collector of the transistor 23, the other collector of the multi-collector transistor 26 is connected to the collector of the transistor 22 to form an active load, and a resistor 24 is connected to the emitter of the transistor 22, and the other collector of the multi-collector transistor 26 is connected to the collector of the transistor 23. One end is connected to the emitter of the transistor 23, a constant current source circuit 25 is connected to the connection point between the resistor 24 and the emitter of the transistor 23, and the other end is grounded to form a comparator. The output from the level detector is supplied from the emitter of transistor 19 to the base of transistor 22 which forms a comparator.

The drive circuit C connects the emitter of the transistor 27 to the base of the multi-collector transistor 28, connects one of the collectors of the multi-collector transistor 28 to the base of the transistor 27, and the collector of the transistor 27 is grounded. The emitter is connected to the power supply voltage _Vcc , and the multi-collector transistor 2
A resistor 29 and a transistor 30 are connected to the other collector of 8.
Connect the base of the resistor 29 and ground the other end of the resistor 29, connect the resistor 31 and the resistor 32 to the emitter of the transistor 30, and connect the strength meter 3 to the other end of the resistor 32.
3 is connected.

The signal from the limiter circuit is applied to the base of transistor 18 via a coupling capacitor. Further, a bias voltage E ₂ is supplied to the base of the transistor 18 via a resistor. The input signal is input to the base of the transistor 19 using the voltage between the terminals of the resistor 21 as a bias, and is converted into a DC voltage.
The transistors 22 and 23 constitute a differential pair, and a voltage E ₁ is applied to the base of the transistor 23, which is equal to the voltage at the emitter of the transistor 19 when there is no signal.
and the voltage supplied to transistor 22,
In other words, when the signal strength of the FM broadcast wave exceeds the potential of voltage _E1 , current is drawn from drive circuit C and resistor 2
A potential is developed across the terminals of the transistor 9, and the transistor 30 becomes active and causes current to flow into the strength meter drive 33. In addition, the transistors 22 and 23
A resistor 24 is connected between the emitters of the transistor 23, and a current source 25 is connected to the emitter side of the transistor 23 for balance. It is designed to absorb electric potential. Since the noise component from the limiter circuit 1 is absorbed by the resistor 24, the noise component is not superimposed on the current when there is no signal and is not supplied to the driver circuit C.

As mentioned above, the strength meter of the FM receiver according to the present invention uses a differential amplifier as a comparator, and applies the emitter potential of transistor Q ₁₉ in advance to the base of transistor Q ₂₃ when there is no signal; By converting the signal strength of the FM broadcast wave into a DC potential from the limiter circuit and supplying it to the base of transistor 22, which forms a differential amplifier with transistor Q ₂₃ , it maintains equilibrium when no signal is input, and the strength meter Leakage current is prevented from flowing, and as the FM broadcast wave signal is input and gradually becomes stronger, current is drawn from the current source circuit consisting of transistors 27 and 28 to drive the strength meter.

In this way, the present invention uses a differential amplifier as a comparison, keeps the differential amplifier at equilibrium when there is no FM broadcast signal, and eliminates the noise from the limiter circuit using the emitter resistor connected to the differential pair of transistors. This prevents leakage current from flowing into the strength meter and prevents the strength meter pointer from swinging due to noise.

As described above, the strength meter circuit of the FM receiver according to the present invention has an excellent effect of preventing the unpleasant deflection of the pointer of the strength meter when there is no signal.

[Brief explanation of the drawing]

Fig. 1 shows a strength meter drive circuit of a conventional FM receiver, and Fig. 2 shows a strength meter drive circuit of an FM receiver according to the present invention. 1: Limiter circuit, 2: Detector, A ₁ , A ₂ ~A
_o , B ₁ , B ₂ to B _o : peak detector, C: strength meter drive circuit.

Claims (1)

[Scope of utility model registration request] In the strength meter drive circuit of an FM receiver, the output from each differential amplifier of a limiter circuit formed from multi-stage differential amplifiers is input to a level detection circuit via a buffer circuit, respectively. comprising means for converting into a DC voltage according to signal strength, and a differential amplifier for detecting the potential of the DC voltage obtained from the means, the differential amplifier comprising first and second transistors forming a differential pair; , a resistor connected between the emitters of these transistors, and a constant current source circuit connected to a connection point between the emitter of the second transistor and the resistor,
A DC voltage corresponding to the input signal intensity is supplied to the base of the second transistor, and a reference voltage corresponding to the voltage generated when there is no signal is supplied to the base of the second transistor, and the input signal intensity is set to the predetermined reference voltage. When the level exceeds the level, the differential amplifier is activated to drive the strength meter, and when there is no signal, the drive current to the strength meter is cut off and the noise generated from the limiter circuit is removed. Features a strength meter drive circuit for an FM receiver.