JPH0630410B2 - Signal processing circuit device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a signal processing circuit for a television receiver or the like, and more particularly, by improving the connection between an audio FM detector and an attenuator to reduce the number of elements and the number of terminals. Then, the present invention relates to a signal processing circuit device capable of forming an audio circuit having an audio direct output terminal.

[Prior art]

Conventionally, as the main signal processing circuit device, for example, a signal processing circuit device as an integrated circuit, there is one shown in FIGS. 1 and 2. In FIG. 1, 1 is an FM detector for detecting an FM audio signal, RL is a load resistance, DO is an audio direct output terminal, C is an external capacitor, AI is an attenuator input terminal, R
1, R2 is a resistor, D1 is a diode, 2 is an attenuator, and in the attenuator 2, Q1, Q2 and Q3 are transistors, R3 is a resistor, V1 is a reference voltage source (constant voltage source), Z
Is an output means, O is an output terminal, Vcc power supply terminal, GND is a ground terminal, VC is a volume control terminal, and Vc is a control power source (variable DC voltage source) for volume adjustment. Further, in FIG. 2, D2 is a diode and Q4 is a transistor. The audio direct output terminal DO is for directly outputting the output of the FM detector 1 to the outside, and is used for recording television sound and the like. Further, as is apparent from the drawing, in the structure shown in FIG. 1, the F inside the frame surrounded by the solid line is shown.
M detector 1, attenuator 2, load resistor RL, resistors R1, R2
The diode D1 and the diode D1 are formed, for example, as an integrated circuit, and in the structure shown in FIG. 2, the FM detector 1, the attenuator 2, and the
The load resistor RL, the resistor R2, the diodes D1 and D2, and the transistor Q4 are formed, for example, as an integrated circuit.

Next, the circuit operation of FIG. 1 will be described. FM detector 1
The current is drawn from the load resistance RL by the detection operation of
A voice signal is generated across the load resistor RL. This audio signal is input to the connection point of the resistor R1 and the diode D1 via the audio direct output terminal DO, the external capacitor C, and the attenuator input terminal AI, and this audio signal is directly supplied to the current by the resistors R1 and R2 and the diode D1. Attenuator 2 superimposed on
Entered in.

The collector current of the transistor Q3 of the attenuator 2 changes according to the audio signal input from the terminal AI, and the current is distributed to the transistors Q1 and Q2 according to the base voltage of both transistors Q1 and Q2. Here, when it is desired to raise the volume of the output terminal O, the control power supply Vc voltage is set to the reference voltage V1.
The control power supply Vc voltage may be set lower than the reference power supply V1 to lower the volume.

Next, the circuit operation of FIG. 2 will be described. Similar to Figure 1.
A current is drawn from the diode D2 by the detection operation of the FM detector 1, and a voice signal is generated at both ends thereof. This audio signal flows through the load resistor RL, the diode D1, and the resistor R2 by the current mirror by the diode D2 and the transistor Q4, is DC biased by the resistors RL, R2, and the diode D1, and is output from the audio direct output terminal DO and the diode D1. Is input to the attenuator 2 by a current mirror including a transistor Q3.

The conventional signal processing circuit device is configured as described above. In the conventional example shown in FIG. 1, since the output DC voltage of the FM detector 1 and the input bias of the attenuator 2 are different from each other, capacitive coupling must be performed externally. Therefore, two external connection terminals DO,
AI is required. Further, when the power supply fluctuates, a fluctuating voltage is generated between the load resistance RL and the GND, and the voltage is output to the output terminal O through the attenuator 2.

Further, in the conventional example of FIG. 2, the output current of the FM detector 1 is passed through the load resistor RL and the diodes D1 and R2 by the current mirror by the diode D2 and the transistor Q4, so that the power supply voltage does not directly change at the output terminal DO. However, there is a drawback in that if a direct sound output is taken out with a sufficiently large amplitude, the DC voltage rises and the dynamic range cannot be obtained.

[Outline of Invention]

The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, in which only the alternating current of the differential output current of the FM detector is passed through the resistor to directly output the voice and the resistor is also used as the attenuator. For the purpose of providing a signal processing circuit device capable of obtaining a direct audio output having a wide dynamic range with a simple circuit configuration and being hardly affected by power supply voltage fluctuations, by connecting to the common emitter of the differential amplifier constituting There is.

Example of Invention

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows a signal processing circuit device according to an embodiment of the present invention, for example, a signal processing circuit device as an integrated circuit. In the figure, the same reference numerals as those in FIGS. In the circuit of this embodiment, the differential output of the FM detector 1 is connected to the cathodes of the diodes D2 and D3 (see FIG. 3).
Together, they are connected to the bases of the transistors Q4 and Q5, respectively. The anodes of the diodes D2 and D3 and the emitters of the transistors Q4 and Q5 are connected to the power source, and Q5
Is connected to the diode D4 and the base of the transistor Q6, the collector of Q4 is connected to the collector of Q6, the resistor RL, and the audio direct output terminal DO, and the cathode of the diode D4 and the emitter of the transistor Q6 are connected to the ground terminal GND. Connected. And the diode D2
~ D4, transistors Q4 to Q6 form a subtraction means 3.

Further, the base of the transistor Q1 is connected to the reference voltage source V1, the base of the handle Q2 is connected to the variable DC voltage source Vc through the volume control input terminal VC, and the transistor Q1 is connected.
The emitters of Q2 and Q2 are commonly connected to the constant current source Io and the load resistor RL. Further, the transistor Q1 or Q2
The collector of is connected to the output means (output load) Z, and the sound whose volume is controlled is output from the output terminal O. As is clear from the figure, the F inside the frame surrounded by the solid line
M detector 1, attenuator 2, subtraction means 3 and load resistance RL
Are, for example, formed as an integrated circuit.

Next, the operation will be described.

As shown in FIG. 4, the two output currents of the FM detector 1 include the DC bias current I1 and the amplitude Δ corresponding to the audio signal.
The AC current of I is superposed differentially and is output.

The two output currents are canceled by the current mirror composed of D3, Q5, D4 and Q6 and the current mirror composed of D2 and Q4, and the DC bias current component I1 is canceled. As a result, the load resistor RL has an AC current of 2ΔI. Flows. Since the reference voltage V1 and the volume control voltage Vc do not include an AC component, the sound direct output terminal DO uses the common emitter voltage of the transistors Q1 and Q2 as a DC bias voltage, and an AC signal voltage of RL × 2ΔI. The superimposed voltage is output.

On the other hand, the current flowing through the common emitter point of the transistors Q1 and Q2 is the sum of the DC bias current Io from the constant current source Io and the AC current of 2ΔI from the load resistor RL, and the DC voltage applied to the bases of the transistors Q1 and Q2. According to the difference, the current is distributed, the current distributed to the transistor Q2 flows to the output means Z connected to its collector,
A volume-controlled signal is taken out from the output terminal O.

As described above, the configuration of the present embodiment requires less external connection terminals. Moreover, since the current mirror is used to output only the difference between the AC signal currents and output to the resistor, there is an effect that a wide dynamic range is provided and a direct audio output that is less susceptible to power supply voltage fluctuations is obtained.

As shown in FIG. 5, a grounded base transistor Q7 may be inserted between the connection point of the load resistor RL and the constant current source Io and the common emitter connection point of the transistors Q1 and Q2, and the constant voltage source V2 may be connected to the base. . Also, the transistor Q
Instead of 7, a resistor R1 may be inserted as shown in FIG. 6, and the same effect as in the above embodiment can be obtained.

〔The invention's effect〕

As described above, according to the present invention, in the signal processing circuit device including the FM detector and the attenuator, only the AC component of the differential output current of the FM detector is passed through the resistor to directly output the sound. Since it is transmitted to the common emitter of the differential amplifier that constitutes the attenuator, the number of external connection terminals is reduced as much as possible, the output dynamic range is wide with a simple circuit configuration, and a sufficiently large output can be taken out. There is an effect that it is possible to configure a signal processing circuit device that can obtain a voice direct output that is less susceptible to power supply voltage fluctuations.

[Brief description of drawings]

1 and 2 are circuit diagrams of a conventional signal processing circuit, FIG. 3 is a circuit diagram of a signal processing circuit according to an embodiment of the present invention,
FIG. 4 is a waveform diagram of each part of FIG. 3, and FIGS. 5 and 6 are circuit diagrams of a signal processing circuit according to another embodiment of the present invention. In the figure, 1 is an FM detector, 2 is an attenuator, 3 is subtraction means, RL is a load resistor, DO is a voice direct output terminal, Io is a constant current source, Q1, Q2 and Q7 are first, second and second. 3 is a transistor, V1 and V2 are first and second constant voltage sources, Vc is a variable DC voltage source, and Z is an output means. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (4)

[Claims] 1. An FM detector that detects an FM audio signal and outputs two output currents in which alternating currents based on the amplitude of the audio signal are superimposed on a DC bias current with opposite polarities, and 2 from the FM detector. Receiving two output currents, these two
Subtracting means for subtracting two output currents and outputting a signal current in which the DC bias current has been canceled to the output node; a direct audio output terminal for outputting an audio signal to the outside, which is connected to the output node of the subtracting means. , A first transistor to which a reference voltage is applied to the base,
An attenuator having a second transistor whose emitter is connected to the emitter of this first transistor, connected to the base of the second transistor of this attenuator,
A volume control input terminal to which a control voltage is applied from the outside, an audio output terminal connected to the collector of the second transistor of the attenuator, for outputting an audio signal whose volume is controlled by the attenuator to the outside, The signal current from the subtracting means is connected between the output node of the subtracting means and the common connection node of the emitters of the first and second transistors in the attenuator, and the signal current from the subtracting means is connected to the first and second transistors in the attenuator. A signal processing circuit device provided with a resistor for transmitting the signal to a common connection node of the emitters and for converting it into an audio signal to the audio direct output terminal as an AC signal voltage based on a signal current from the subtracting means. 2. One end of the resistor is the first and second ends of the attenuator.
The signal processing circuit device according to claim 1, wherein the signal processing circuit device is directly connected to a common connection node of the emitters of the transistors. 3. The attenuator has a third transistor connected between a common connection node of the emitters of the first and second transistors and one end of the resistor, and having a predetermined potential applied to the base. The signal processing circuit device according to claim 1, wherein 4. The attenuator has a resistor connected between a common connection node of the emitters of the first and second transistors and one end of the resistor. The signal processing circuit device according to the item.