JPS6233384Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an S-curve voltage generation circuit in a radio receiver or the like.

When a quadrature detection circuit is used as a detection circuit, the detection output is not at O level but at the reference voltage of the quadrature detection circuit, for example a (V), when there is no signal and when tuning. Therefore, when creating an S-curve voltage based on such a detection output,
The tuning center voltage is also a(V). On the other hand, automatic frequency control (hereinafter referred to as AFC) uses S-curve voltage.
When performing AFC operation by driving a circuit called
(V) It may be necessary to apply an S-curve voltage of (V) to the AFC circuit. The present invention provides an S-curve detection circuit that facilitates adjustment to generate an S-curve voltage of b(V) when using a quadrature detection circuit having a reference voltage of a(V).
A curve voltage generation circuit is provided.

Hereinafter, a detailed description will be given with reference to embodiments shown in the drawings.

In FIG. 1, 1 is an intermediate frequency amplifier circuit, 2 is a quadrature detection circuit, 3 is an audio frequency amplifier circuit, 4 is a muting circuit, 5 is an operational amplifier circuit, and 6 is a variable resistor for adjusting offset voltage. A reference voltage (for example, 5.56V) is derived from the A output of the quadrature detection circuit 2 (Fig. 2a).
reference). A detection output (see Figure 2b; only the S curve signal is shown) is obtained from the B output of the quadrature detection circuit 2, and this is amplified by the audio frequency amplification circuit 3 (see Figure 2C). . Due to the offset voltage in the audio frequency amplifier circuit 3, the detection output voltage at the time of complete tuning does not necessarily reach the reference voltage (5.56V) of the quadrature detection circuit 2, but a voltage slightly lower than this, for example, about 5.1V, appears. Now, the reference voltage (5.56V) output from the quadrature detection circuit 2 and the detection output output from the audio frequency amplifier circuit 3 are input to the operational amplifier circuit 5, and an S-curve output is obtained from the output side (Fig. 2). (see d). And the tuning center voltage of this S curve output is a predetermined voltage (for example, 4.75V)
The input offset voltage is adjusted by operating the adjustment resistor 6 so that

By the way, when performing such adjustment, the output of the audio frequency amplifier circuit 3 is a constant voltage (5.1V in the previous example) in the no-signal state, so the output of the operational amplifier circuit 5 is at a predetermined voltage. All you have to do is adjust the adjustment resistor 6 so that the tuning center voltage (4.75V in the previous example) is reached, but in reality, even when there is no signal, the output of the audio frequency amplification circuit 3 may be affected by external noise etc. Due to fluctuations, adjustment work was difficult, and it was difficult to obtain the specified 4.75V accurately.

Therefore, in the present invention, a muting circuit 4 is provided to suppress the above fluctuations when there is no signal. The muting circuit 4 is driven when the level of the intermediate frequency signal is below a predetermined value, and sets the audio frequency amplifier circuit 3 to a muting state (see FIG. 2e). At this time, the output of the audio frequency amplification circuit 3 is not affected by external noise and becomes a constant voltage (5.1V). Therefore, adjustment is easy,
And it will be accurate. Then, when the level of the intermediate frequency signal exceeds a predetermined value in the signal reception state, the muting state is canceled and the output of the audio frequency amplification circuit 3 changes based on the S curve characteristic, and the output of the operational amplifier circuit 5 changes. From this, it is possible to obtain an S-curve voltage with a tuning center voltage of 4.75V.

According to the present invention described above, when adjusting the offset voltage of the operational amplifier circuit in order to obtain an S-curve output with a desired voltage as the tuning center voltage, the adjustment is made without being affected by external noise. This makes it easy to work with and allows accurate adjustment.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an S-curve voltage generation circuit according to the present invention, and FIGS. 2 a to 2 e are diagrams showing waveforms at various parts in FIG. 1. 2... Quadrature detection circuit, 4... Muting circuit, 5... Operational amplifier circuit, 6... Variable resistor for adjusting offset voltage.

Claims (1)

[Scope of utility model registration request] A quadrature detection circuit whose reference voltage is a (V), an amplifier circuit that amplifies the detection output from this quadrature detection circuit, and a detection output amplified by this amplifier circuit and the reference voltage of a (V). An operational amplifier circuit that outputs an S-curve voltage with b(V) (a≠b) as an input and a tuning center voltage, an offset voltage adjustment circuit connected to the input side of this operational amplifier circuit, and an intermediate frequency signal. A muting circuit that detects the level and controls the amplifying circuit when there is no signal is provided, and by controlling the amplifying circuit with the muting circuit when there is no signal, fluctuations in the detected output from the amplifying circuit are prevented. An S-curve voltage generation circuit characterized by: