JPH0641398Y2 - FM receiver level shift circuit - Google Patents

Description

[Detailed Description of the Device] (a) Field of Industrial Application This device relates to a level shift circuit of an FM receiver, and in particular,
The present invention relates to a level shift circuit of an FM receiver suitable for reducing noise of high frequency components due to weak electric field strength and controlling the degree of separation of stereo signals.

(B) Prior art As a level shift circuit of a conventional FM receiver, for example,
The thing as shown in FIG. 2 was provided.

In the figure, 1 is a receiving antenna, 2 is a front end circuit, 3 is an IF amplifier, 4 is an FM demodulation circuit, 5 is a high cut circuit, 6 is an MPX and separation blend circuit, and 7 is L.
A channel output terminal, 8 is an R channel output terminal, 9 is an electric field strength indicator, 10 electric field strength detection circuits, 19 to 22 are resistors, and 23 is a level shift diode.

As for the circuit configuration, the receiving antenna 1 is connected to the front-end circuit 2, the front-end circuit 2 passes through the IF amplifier 3, the FM demodulation circuit 4 and the high-cut circuit 5, and further,
It is connected to the MPX and separation blend circuit 6.

From the MPX and separation blend circuit 6, L channel signal output terminal 7 which is a stereo audio signal, and R
The channel output terminals 8 are connected to the next-stage AF amplifiers, respectively.

Further, a part of the IF signal is taken out from the IF amplifier 3 and connected to the electric field strength detection circuit 10,
Is connected to the electric field strength indicator meter 9.

Further, the output of the electric field strength detection circuit 10 is connected to the anode side of the level shift diode 23.

The cathode side of the level shift diode 23 is a resistor 19 and
The MPX and the separation blend circuit 6 are connected to the high-cut circuit 5 via a voltage dividing circuit composed of 20, and also via the voltage dividing circuit composed of resistors 21 and 22.
It is connected to the.

Explaining the operation of the level shift circuit having the above configuration, the IF signal applied from the IF amplifier 3 to the electric field strength detection circuit 10 becomes a DC level voltage according to the received strength by the electric field strength detection circuit 10 and the anode of the level shift diode 23. Is applied to the side of the level shift diode 23, and the voltage is level-shifted by the forward voltage of the level shift diode 23 and output to the cathode side of the level shift diode 23.

The voltage level-shifted by the level shift diode 23 is set to a voltage level for controlling the high-cut circuit 5 by the voltage dividing circuit formed by the resistors 19 and 20 and applied to the high-cut circuit 5.

Similarly, a voltage dividing circuit constituted by the resistors 21 and 22 sets the voltage level to control the MPX and the separation blend circuit 6 and applies the voltage level to the MPX and the separation blend circuit 6.

As described above, in the conventional example, when the DC level signal output from the electric field strength detection circuit 10 is level-shifted and used as a control signal for the high-cut circuit 5, MPX, separation blend circuit, etc., the level shift is performed. The voltage value is defined only by the forward voltage of the level shift diode 23.

(C) Problems to be solved by the device However, in the level shift circuit of the conventional FM receiver described above, as shown in FIG. 2, the voltage level output from the electric field strength detection circuit 10 is level-shifted to a high cut level. When used as a control signal for the circuit 5, MPX and high blend circuit 6, the level shift can be adjusted only by the forward voltage of the level shift diode 23, and the high cut circuit 5 and
There was a difficulty in providing the optimum control signal level to the characteristics of the MPX and the high blend circuit 6.

The present invention has been made in view of the above points, and the purpose thereof is to eliminate the drawbacks of the conventional example, and to arbitrarily select the signal from the electric field strength signal detection circuit to be supplied to the high cut circuit, MPX and high blend circuit. The level shift circuit of the FM receiver is provided so that the level shift voltage can be set to the value of and the optimum high cut characteristics and separation blend characteristics are obtained.

(D) Means for solving the problem The level shift circuit of the FM receiver of the present invention detects the IF signal and the electric field strength detection circuit which inputs the IF signal output from the IF amplifier to detect the electric field strength level. A high-cut circuit controlled by a DC voltage for cutting high-frequency components included in the obtained audio signal, and an MPX circuit that separates a stereo signal obtained by detecting an IF signal into L and R components , FM that combines the L and R components provided in this MPX circuit and controls the separation blend circuit controlled by the DC voltage for changing the stereo sense, and the electric field strength detection circuit, the high cut circuit and the separation blend circuit In the level shift circuit of the receiver, an electric field constituted by a FET and a transistor is provided between the electric field strength detection circuit and the high cut circuit and separation blend circuit. A pressure shift circuit is provided and the high cut circuit and the separation blend circuit are controlled by the electric field strength.

(E) Function According to this invention, the IF signal output from the IF amplifier is input and the electric field strength detection circuit that detects the electric field strength level and the IF
A high-cut circuit controlled by a DC voltage for cutting wide-range frequency components included in the audio signal obtained by detecting the signal, and a stereo signal obtained by detecting the IF signal as L
And R component. The MPX circuit, the separation blend circuit controlled by the DC voltage for mixing the L and R components provided in the MPX circuit to change the stereo feeling, the electric field strength detection circuit, the high cut circuit and the separation blend circuit are provided. In the level shift circuit of the FM receiver to be coupled, a voltage shift circuit composed of FET and transistor is provided between the electric field strength detection circuit and the high cut circuit and separation blend circuit, so it automatically changes according to the change of electric field strength. It becomes possible to control the blending amounts of the L and R signals which are stereo signals of the high cut circuit and the separation blend circuit.

(F) Embodiment An embodiment of the level shift circuit of the FM receiver according to the present invention will be described with reference to FIG.

The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a circuit diagram of this device.

In the figure, 11 is a FET, 12 is a transistor, 13 is a voltage source, 14 is a semi-fixed resistor, and 15 to 18 are resistors.

Explaining the circuit configuration, the front-end circuit 2, the IF amplifier 3, the FM demodulation circuit 4, the electric field strength indicator meter 9, and the electric field strength detection circuit 10 are the same as those in the conventional example, and therefore their explanations are omitted.

A DC level signal, which is output from the electric field strength detection circuit 10 and is proportional to the electric field strength, is connected to the gate of the FET 11 and the resistance 15 of the bias resistor is connected between the gate and the ground.

The drain side of FET11 is connected to the positive power supply voltage + Vcc,
The source side is connected to the collector of the transistor 12 via the resistor 16.

The base side of the transistor 12 is connected to a voltage divider circuit that divides the voltage source 13, which is composed of a resistor 17 and a semi-fixed resistor 14, and the emitter of which is a negative power source voltage − via a resistor 18.
In the circuit connected to Vcc, the base voltage (VB) obtained by this voltage dividing circuit causes the emitter voltage of the transistor 12 to be a constant potential lower than the base voltage by the forward voltage between the base and the emitter. The current flowing through the collector of is approximately {emitter potential-(-Vcc)} / emitter resistance value, which is a so-called constant current source circuit.

Further, from the collector of the transistor 12, resistors 19, 20 and
High cut circuit 5 and MP through the voltage dividing circuit by 21 and 22
It is connected to the X and separation blend circuit 6.

As the operation of the level shift circuit configured as described above, a signal voltage of a DC level proportional to the electric field strength output from the electric field strength detection circuit 10 is applied as a bias voltage to the gate of the FET 11 by the resistor 15 and is applied to the source of the FET 11. Since the constant current circuit consisting of the transistor 12 is connected to the connected resistor 16, the FET 11 is in the operating state, and the voltage at the connection point between the resistor 16 and the collector of the transistor 12 is the resistance due to the current flowing in the constant current circuit. It is the value of the voltage drop that occurred in 16. Therefore, the level is shifted by the voltage drop generated in the resistor 16 in proportion to the voltage applied to the gate of the FET 11.

As the operation of the constant current circuit by the transistor 12, the current value flowing through the resistor 18 can be changed by changing the base bias voltage of the transistor 12 with the semi-fixed resistor 14, and the current value flowing through the resistor 18 is equal to the base current of the transistor 12. Since it is the sum of the drain-source current of the FET 11 flowing through the resistor 16, the current flowing through the resistor 19 and the current flowing through the resistor 21, the voltage drop level generated in the resistor 16 can be set arbitrarily by changing the current value flowing through the resistor 18. Can be set to. It becomes possible to set optimum resistance values in the high-cut circuit 5, the MPX, and the separation blend circuit 6, respectively, and apply the best control voltage.

(G) Effect of the device According to the level shift circuit of the FM receiver according to the present invention,
Since a voltage shift circuit composed of FET and transistor is provided between the electric field strength detection circuit, high cut circuit, MPX and separation blend circuit, the gain difference between the front end and the IF amplifier depends on the electric field strength. Even if occurs, the high-cut circuit and the optimum control voltage
There is an effect that the MPX and the separation blend circuit can be operated.

Moreover, it has excellent features such as a simple structure and easy implementation.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a level shift circuit of an FM receiver according to the present invention. FIG. 2 is a circuit diagram of a conventional example. Description of main drawings 1: Reception antenna 2: Front end circuit 3: IF amplifier 4: FM demodulation circuit 5: High-cut circuit 6: MPX and separation blend circuit 7: L audio signal output terminal 8: R audio signal output terminal 9: Electric field strength indicator 10: Electric field strength detection circuit 11: FET 12: Transistor 13: Voltage source 14: Semi-fixed resistance 15 to 22: Resistance

Claims (1)

[Scope of utility model registration request] 1. An electric field strength detection circuit for detecting an electric field strength level by inputting an IF signal output from an IF amplifier, and for cutting a high frequency component included in a sound signal obtained by detecting the IF signal. High-cut circuit controlled by DC voltage and stereo signal obtained by detecting IF signal is L and R
MPX circuit for separating into components and L provided in this MPX circuit
In the level shift circuit of the FM receiver, which combines a separation blend circuit controlled by a DC voltage for blending R and R components to change a stereo feeling, and an electric field strength detection circuit, a high cut circuit and a separation blend circuit, A voltage shift circuit composed of a FET and a transistor is provided between the electric field strength detection circuit and the high cut circuit and separation blend circuit, and the high cut circuit and the separation blend circuit are controlled by the electric field strength. Level shift circuit of receiver.