JPH0737378Y2 - S meter voltage shift circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial application> The present invention relates to an S-meter voltage shift circuit of a radio receiver, and more particularly to an S-meter voltage shift circuit capable of continuously changing the voltage level of an S-meter voltage signal.

<Prior Art> In a radio receiver, the S / N ratio can be improved by changing from stereo to monaural or by attenuating (high-cutting) high frequencies in a weak electric field where the noise level becomes large.
Therefore, the radio receiver for use in vehicles receiving conditions change according to the running of the automobile, channel separation control circuit and high-cut control circuit is provided, the received field strength as shown in FIG. 4 is E ₁ or less In this case, the degree of channel separation is weakened to give a monaural tendency, and when the received electric field strength becomes E ₂ or less, the high cut amount is increased as the received electric field strength becomes weaker. Incidentally, 1 is a channel separation characteristic, and 2 is a high cut characteristic.

Such a radio receiver is provided with an S meter circuit having a predetermined input / output characteristic (input / output characteristic 3 in FIG. 4) in order to detect the received electric field strength, and the S meter voltage output from the S meter circuit is provided. Separation and high-cut control are performed based on the signal SMin.

By the way, the levels E ₁ and E ₂ and the slope in the channel separation characteristic and the high cut characteristic differ depending on the area where the FM receiver is used. That is, whether the area where the radio receiver is used is a strong electric field area with a lot of multipath noise (for example, an urban area), a weak electric field area with little noise (for example, a wilderness with few obstacles, a coast, etc.), or adjacent interference. Channel separation characteristics and high cut characteristics differ depending on whether or not there is a region. For this reason, the radio receiver is provided with a shift circuit for changing the voltage level of the S meter voltage signal SMin, changing E ₁ and E ₂ by shifting, and a characteristic changing circuit for changing the inclination of each characteristic.

FIG. 5 is a block diagram of the main part of the radio receiver. 11 is an antenna, 12 is a front end, 13 is an intermediate frequency amplifier, and 14
Is a detector, 15 is a noise killer, 16 is a stereo demodulation circuit,
Reference numeral 17 is connected to the intermediate frequency amplifier 13 and outputs S meter voltage signal SMin having a voltage value according to the received electric field strength E.
When the separation control voltage Vsc is below the set level Ls, 18 is a separation control circuit which weakens the degree of separation to make a monaural tendency as shown in FIG. 4, and 19 is a high cut control voltage Vhc set level Lh. When it becomes the following, as shown in Fig. 4, as the received electric field strength becomes weaker, the amount of high-frequency attenuation (high-cut amount) becomes higher.
Is a high-cut circuit that increases

Reference numeral 20 denotes a shift circuit that shifts the voltage level of the S meter voltage signal SMin, and shifts the level of the S meter voltage signal by using a diode or the like having a constant voltage characteristic. Reference numeral 21 is a characteristic changing circuit, which is a separation characteristic changing section for changing the inclination of the channel separation characteristic.
21a and a high-cut characteristic changing section 21b for changing the inclination of the high-cut characteristic.

FIG. 6 is an example of the shift circuit 20 for the S-meter voltage signal SMin. The shift voltage signal SMout shifted by the sum Vsft (= Vbe + Vf) of the base-emitter voltage Vbe of the transistor Tr and the voltage drop Vf of the diode D is shown in FIG. It is obtained from the output terminal (see FIG. 7). The transistor Tr generates Vbe and also operates as a buffer. This is the resistance RL
This is because the load is relatively low, so that the load does not become heavy.

<Problems to be solved by the invention> However, in the conventional shift circuit, the S meter signal voltage SMin
The shift amount was constant. Therefore, due to variations in the ICs that make up the intermediate frequency amplifier, the S meter voltage signal SMin
If the level of fluctuated, it could not be corrected.

Further, the voltage shift amount can be changed by changing the number of diodes connected in series (see the dotted line in FIG. 6) or by connecting the diodes having different shift amounts, but the change amount of the shift amount becomes troublesome. However, there is a problem that the shift amount cannot be changed continuously (only discretely), and it is impossible to perform fine level fluctuation correction, separation, and change control of high-cut characteristics.

From the above, an object of the present invention is to provide an S-meter voltage shift circuit capable of continuously changing the voltage level of the S-meter voltage signal with a simple circuit configuration.

<Means for Solving the Problem> In the present invention, the above problem is that the S meter voltage signal SMin is input to one input terminal and the output voltage is input to the other input terminal.
This is achieved by an operation amplifier having a gain of 1 to which an intermediate voltage between Vout and the bias voltage Vb is fed back and a bias voltage adjusting circuit that changes the bias voltage Vb.

<Operation> The output voltage Vout of the operational amplifier is the input voltage Vi
If n, then Vout = Vin-Vb. Therefore, by changing the bias voltage Vb, the voltage signal Vout obtained by continuously shifting the S meter voltage signal SMin can be obtained.

<Embodiment> FIG. 1 is a circuit diagram of an embodiment of an S-meter voltage shift circuit according to the present invention, in which 11 is an input section composed of resistors R ₁ and R ₂ ,
12 is a bias voltage adjusting circuit that generates a bias voltage Vb with a variable resistor VR 1 and a fixed resistor R _5, and 13 is a feedback unit configured with resistors R ₃ and R ₄ for feeding back an intermediate voltage between the output voltage Vout and the bias voltage Vb. , 14 are operation amplifiers to which the S meter voltage signal SMin is input to the + input terminal and the intermediate voltage between the output voltage Vout and the bias voltage Vb is fed back to the-input terminal. The gain of the operational amplifier can be set to 1 by setting R ₁ = R ₂ = R ₃ = R ₄ .

In this S meter voltage shift circuit, the bias voltage
If Vb, the output voltage Vout is given by Vin ′ = R ₂ · Vin / (R ₁ + R ₂ ) Vout = [(R ₃ + R ₄ ) · Vin ′ / R ₃ ] −Vb, and R ₁ = R ₂ = When R ₃ = R _4, the Vout = Vin-Vb.

Therefore, when the bias voltage Vb is changed to 0 → a → b → c using the variable resistor VR1 of the bias voltage adjusting circuit 12, the output voltage Vout also continuously changes as shown in FIG.

In Fig. 3, the bias voltage Vb is 0 → + 1V → + 2V → + 3V → + 4V
It is a measured value characteristic of the voltage shift circuit according to the present invention when changed to.

<Advantages of Device> According to the present invention, the operation of gain 1 in which the S meter voltage signal SMin is input to one input terminal and the intermediate voltage between the output voltage Vout and the bias voltage Vb is feedback input to the other input terminal. Since the shift circuit is configured by the amplifier and the bias voltage adjusting circuit for changing the bias voltage Vb, and the bias voltage Vb is changed by the variable resistor or the like, the S meter voltage signal SMin is continuously shifted. It is easy to change the shift amount, and it is now possible to perform fine level fluctuation correction, separation, and high cut characteristic change control.

[Brief description of drawings]

FIG. 1 is an S meter voltage shift circuit according to the present invention, FIG. 2 is an example of S meter voltage signal shift according to the present invention, FIG. 3 is an actual shift characteristic diagram of the S meter voltage signal, and FIG. Of characteristics, separation characteristics and input / output characteristics of S meter, FIG. 5 is a block diagram of a radio receiver including a conventional shift circuit, FIG. 6 is a conventional shift circuit, and FIG. 7 is a conventional shift characteristic. is there. 11 …… Input section 12 …… Bias voltage adjustment circuit 13 …… Feedback section 14 …… Operation amplifier

Claims (1)

[Scope of utility model registration request] 1. An S meter voltage shift circuit for shifting a voltage level of an S meter voltage having a value according to a received electric field strength, wherein an S meter voltage signal is input to one input terminal and an output voltage is input to the other input terminal. And an operation amplifier having a gain of 1 to which an intermediate voltage of the bias voltage is fed back, and a bias voltage adjusting circuit for changing the bias voltage, and changing the bias voltage to change the shift amount of the S meter voltage signal. And S meter voltage shift circuit. S meter circuit.