JPH0133045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention can effectively reduce the shock noise generated when power is turned on and off by muting, and is particularly suitable for preventing shock noise in semiconductor integrated circuits. It provides a circuit.

FIG. 1 shows a block diagram of a shock noise prevention circuit that has been widely used in the past. In the figure, 2 is a differential amplifier circuit with large input impedance and large voltage gain, 5, 6, 7 and 1.
2 is a resistor and a capacitor for a bias circuit that provides a DC bias point for the differential amplifier circuit; 3 is an electronic switch that can be turned on or off by a control circuit; 4 is an electronic switch that makes the electronic switch 3 conductive when the power is turned on or off; This is a control circuit that turns off the electronic switch during normal operation.

Note that the circuit portion within the dotted line frame 26 is a portion that can be integrally integrated into a silicon substrate, for example, and in this case, 18 to 22 become external terminals of the semiconductor integrated circuit. Further, resistors 8 to 10 and capacitors 11, 12, and 14 are external elements, and input/output terminals are 1 and 17.

The operation of the shock noise reduction circuit shown in FIG. 1 will be explained. When the power is turned on and off, the voltage at the output terminal 19 of the differential amplifier circuit 2 changes rapidly over time, which causes shock noise, but in the circuit shown in FIG.
By making the switch 3 conductive during this period, the waveform at the output terminal 19 can be prevented from being transmitted to the subsequent circuit, and the shock noise can be effectively reduced. By the way, the capacitor 14 is provided because the DC bias point of the differential amplifier circuit 2 is different from the voltage when the switch 3 is turned on, that is, the potential of the ground point. In the conventional shock noise prevention circuit, this capacitor 14 is essential, so by adding the shock noise prevention circuit, the number of input/output terminals increases. Therefore, when the circuit is integrated into a semiconductor circuit, the number of external terminals increases.

According to the present invention, it is possible to effectively reduce the shock noise when the power is turned on and off without increasing the number of input/output terminals. The shock noise reduction circuit of the present invention will be explained below. FIG. 2 shows a block diagram of a shock noise reduction circuit according to the present invention. Similar to FIG. 1, the portion surrounded by the dotted line frame 34 is a portion that can be made into a semiconductor integrated circuit, for example, and the other elements are external components. In FIG. 2, 2 is a differential amplifier circuit similar to that in FIG. 1, and resistors 5, 6, 7, and 12 are resistors and capacitors for a bias circuit similar to those in FIG. Further, 3 and 32 are electronic switches that can be turned on or off by the control circuit 31. When the power is turned on or off, the control circuit 31 makes the switch 3 conductive and turns off the switch 32, and on the other hand, During normal operation,
A control operation is executed to turn off the switch 3 and turn on the switch 32. Incidentally, unlike in FIG. 1, the output of the differential amplifier circuit 2 is connected to an external terminal 33 via an electronic switch 32 controlled by a control circuit 31. Further, a wiring from the voltage branch point 15 with resistors 6 and 7 similar to that shown in FIG. 1 is connected to the other end of the electronic switch 3 whose one end is connected to the external terminal 33, The control circuit 31 also controls the on/off state. The resistor 10 in FIG. 1 can be omitted from the external circuit elements in FIG. There are now four terminals, one less than the conventional one. Next, the operation of the shock noise prevention circuit of the present invention will be explained.

In the shock noise prevention circuit of the present invention, unlike the conventional example, when the switch 3 is conductive, the output terminal 33
Since the DC bias of the differential amplifier circuit 2 is equal to the output DC bias of the differential amplifier circuit 2, there is no change in the output voltage when switches 3 and 32 are switched. There is no need for direct current cutting. On the other hand, when the power is turned on or off, the voltage of the DC bias circuit is
This voltage changes slowly depending on the time constants of the capacitor 12 and the resistors 6 and 7, so it is possible to reduce the shock noise when the power is turned on and off. In this way, the shock noise prevention circuit of the present invention effectively reduces the shock noise when the power is turned on and off without increasing the number of input/output terminals that become external terminals when it is implemented as a semiconductor integrated circuit. be able to.

FIG. 3 shows a specific circuit example of the present invention. In FIG. 3, a block 35 surrounded by a dotted line corresponds to the bias circuit in FIG. 2, a block 36 corresponds to the differential amplifier circuit in FIG. 2, and a block 37 corresponds to the switch 3 in FIG. The corresponding clamp circuit, block 38, is the control circuit 3 of FIG.
This circuit corresponds to No. 1, and the circuit operation will be described below.

The bias circuit 35 as its output DC voltage
V _CC・R ₂ /(R ₁ + R ₂ ) and external capacitance 1
2 has a longer time constant.

The differential amplifier circuit 36 is a circuit often used in operational amplifiers, and can also have the function of the switch 32 by turning on and off transistors Q ₁ and Q ₁₀ forming constant current sources.

The clamp circuit 37 is a circuit that clamps the output of the amplifier to the potential of the bias circuit, and transistors Q ₁₃ and Q ₁₄ operate when the power is on, and transistors Q ₁₆ and Q ₁₇ operate when the power is off.

The control circuit 38 includes the differential amplifier circuit 3
It controls the constant current source transistor 6 and the clamp circuit 37, and the voltage at the voltage branch point
When V _Z <2V _D , this corresponds to when _the power is turned on, and Q ₁₃ and Q ₁₄ of circuit blocks 36 and 37 are turned on, and Q ₁ , Q ₁₀ , Q ₁₆ and Q ₁₇ are turned off.

When 2V _D < V _Z < V _CC -2V _D , this corresponds to normal operation, with Q ₁ and Q ₁₀ turned on and Q ₁₃ , Q ₁₄ , Q ₁₆ and Q ₁₇ turned off.

Next, when V _Z > V _CC -2V _D , this corresponds to when the power is turned off, and Q ₁₆ and Q ₁₇ are turned on and Q ₁ , Q ₁₀ , Q ₁₃ and Q ₁₄ are turned off, so the power is turned on and When off,
The potential of the bias circuit is output, and during normal operation, the output of the differential amplifier is output as is.

As explained above, the shock noise prevention circuit of the present invention has the effect of preventing the output of the differential amplifier from being output to the output terminal when the power is turned on or off, thereby preventing the generation of shock noise. Since the structure has a reduced number of terminal sections compared to conventional circuits, it is particularly suitable for converting the circuit into a semiconductor integrated circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional shock noise prevention circuit, FIG. 2 is a block diagram showing an embodiment of the shock noise prevention circuit of the present invention, and FIG. 3 is a specific example of the shock noise prevention circuit of the present invention. FIG. 2 is a diagram showing a circuit configuration. 1...Input terminal, 2...Differential amplifier circuit, 3, 3
2...Switch, 31...Control circuit,
5, 6, 7...Resistance for DC bias circuit, 8-1
0...Resistance, 11,12,14...Capacitor,
15... Voltage division point, 17... Output terminal, 18~
22, 33...terminal.

Claims (1)

[Claims] 1. A differential amplifier that amplifies the input signal, a voltage generator that has a time constant that gradually changes when the power is turned on and off and generates a predetermined voltage, and a control circuit that operates when the output of the voltage generator is applied. and first and second switch means that operate as a switch under the control of the control circuit, and the first switch means is disposed between an output generation point and an output terminal of the differential amplifier, The second switch means is disposed between the output generation point of the voltage generation section and the output terminal, and further, one input terminal of the differential amplifier is connected to the voltage generation section, A control circuit executes a control operation that disconnects and conducts the first and second switch means, respectively, when the power is turned on and off, and conducts and disconnects the first and second switch means, respectively, during normal operation. A shot noise prevention circuit characterized by: