JPH0429253B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an input switching type electronic switch circuit, and more particularly to an improved circuit in which switching noise and switching errors do not occur.

2. Description of the Related Art Conventionally, an electronic switch circuit configured as shown in FIG. 1 is known as an electronic switch circuit used in an equalizer switching circuit or the like in an audio device.

In other words, this is an input switching type analog switch circuit using bipolar transistors.
The transistors Q1 to Q8 connected between the positive and negative power supplies +VCC and -VEE form a roughly double-balanced differential circuit configuration, and the transistors Q3 and Q6
By selectively supplying a switching voltage to each base X, Y of It derives the signal. Note that transistors Q7 and Q8 are for current mirrors.

By the way, in this case, while the transistor Q3 is on, the transistor Q6 is off, so the transistor Q4 is off. For this reason,
The coupling capacitor CB on the signal source B side, which is charged when the transistor Q4 is on, is discharged via the resistor RB.

Here, the potential of the output terminal OUT immediately after the transistor Q3 is turned on is as shown in part A of FIG.
From 0 potential, the base of transistor Q1 becomes resistor RA
After short-circuiting and increasing the offset potential to +VBO when biased, it decreases with a time constant determined by the coupling capacitor CA and resistor RA on the signal source A side and settles at the steady state potential -VB. become. If the switching voltage is switched to the transistor Q6 side in this state, the potential at the output terminal OUT rises by one step again to the above-mentioned offset potential +VBO as shown in the lower part of Fig. 2, and then returns to the steady state potential -VB. This will result in a decline.

However, such large fluctuations in the output potential immediately after switching are undesirable because they are transmitted to the outside as switching noise without being corrected.

The idea of eliminating switching noise, which is a drawback of the circuit shown in FIG. 1, is already well known from the content described in Japanese Patent Laid-Open No. 75981/1983. However, JP-A-54-
In the circuit described in No. 75981, since the current flowing to the input transistor 6 and the current flowing to the compensation transistor 32 are supplied from separate current sources 28 and 36, a current error occurs between each current source 28 and 36. This easily manifested itself as an error in the output level, making it impossible to obtain complete compensation.

Therefore, the present invention has been made in view of the above points, and is an extremely good and improved method that can simply and reliably prevent the generation of switching noise and also prevent the generation of error current in the current source. The purpose of this invention is to provide an input switching type electronic switch circuit.

That is, the input switching type electronic switch circuit according to the present invention is provided with a second transistor whose base is common to the first transistor for input, and a current equal to the current flowing when the first transistor is in the on state is transferred to the first transistor. Switching noise and switching errors are avoided by making the current flow to the second transistor when the transistor is off, and by configuring a common current source that flows the current to the first and second transistors. It has the characteristics of

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

That is, as shown in FIG. 3, one end of the signal source A is grounded, and the other end is grounded with a coupling capacitor CA and a bias resistor RA connected in series.
A midpoint A between the capacitor CA and the resistor RA is connected to the base of an input transistor Q11 constituting one switching circuit 11.

Here, the input transistor Q11 and the diode-connected input transistor Q12 form a differential pair, and their common emitter is connected to the collector of the switching transistor Q13. The switching transistor Q13 has its base connected to one switching voltage supply terminal X, and its emitter connected to the negative power supply -VEE via the constant current source 11.

A compensation transistor Q14 whose base is commonly connected to the base of the input transistor Q11 has its collector connected to the positive power supply +VCC, and its emitter connected to the collector of the transistor Q15. A transistor Q16 having a common base and common emitter relationship with this transistor Q15 has its base connected to the negative power supply -VEE via the bias power supply VA, and its emitter connected to the emitter of the switching transistor Q13. is the positive power supply +
Connected to VCC.

The above is one switching circuit 11 in the left half of the diagram.
The other switching circuit 21 section in the right half of the figure is completely symmetrical with the one switching circuit 11 section, and includes a signal source B and a coupling capacitor.
CB, resistor RB, input transistor Q21, diode-connected output transistor Q22, switching transistor Q23, compensation transistor Q24, transistors Q25, Q26 constant current source I
2. Switching voltage supply terminal Y, bias power supply
VB, and the connection relationship will be omitted.

In the figure, OUT is the diode-connected output transistor Q12, Q of both switching circuits 11, 21.
This is an output terminal connected to the common base of 22.

In addition, Q31 and Q32 are both switching circuits 11 and 21.
A transistor forming a current mirror shared by the differential pair transistors Q11, Q12 and Q21, Q22, and is connected between the collector circuit of the transistor and the positive power supply +VCC.

Therefore, in the above configuration, one switching circuit 1
If the switching voltage supply terminal X in 1 is at low level L, the transistors Q11, Q
12, Q13 is turned off. Transistor Q1
4, Q15, and Q16 are turned on. Since transistor Q13 is off, transistor Q
15 and Q16, if pairability is ensured, a current I1/2 will flow in each of them, and the transistor Q
15, and current I1/2 flows to transistor Q14. Transistor Q16 is transistor Q14
This is to cause current to flow through I1/2. The base current of transistor Q14 is connected to the coupling capacitor CA
is charged and enters steady state.

In this state, the switching power supply end
Suppose that is switched to high level H, transistors Q14, Q15, and Q16 are off this time,
Transistors Q11, Q12, and Q13 are turned on. At this time, a current I1/2 flows through the input transistor Q11.

In other words, the base current of the resistor RA when the transistor Q11 is turned on and the base current when the transistor Q14 is turned on are respectively I1/2β. Therefore, if the pairability between the input transistor Q11 and the compensation transistor Q14 is ensured, both base currents, that is, the input potential at point A will not change at all before and after switching, and switching noise can be prevented.

This also applies to point B of the other switching circuit 21.

That is, if the switching voltage supply terminals X and Y are alternately switched to low level and high level, diode-connected input transistors Q12 and Q22
One of the two will always be on,
Moreover, since the input potential does not fluctuate, it is possible to prevent switching noise from occurring and being transmitted to the outside.

Transistor Q1, one of which is in the on state
1, constant current source 11 is shared for the current flowing to Q14, therefore transistors Q11 and Q14
Errors in the current flowing through the circuit can be eliminated.

FIG. 4 shows another embodiment, in which the input/output transistors Q11, Q12 and Q2 of FIG.
1 and Q22, respectively, diode-connected transistors Q11a, Q12a and Q21a,
Q22a is connected in series to increase the withstand voltage.

In addition, in Fig. 4, the switching voltage supply terminal X,
Y is a diode-connected transistor Q41, Q4
2 into one terminal, it is possible to switch between the left and right inputs by switching between high and low levels. In addition,
Resistors R1-R3 and transistors Q43-Q4
6 is the bias power supply VA, VB and I1, I
2.

In the embodiment shown in FIG. 4, the third
As in the case shown in the figure, it is possible to prevent the occurrence of switching noise and also to prevent the occurrence of error current of the current source.

It goes without saying that the present invention is not limited to the embodiments described above and illustrated, and that various modifications and applications can be made without departing from the gist of the invention.

Therefore, as detailed above, according to the present invention, there is provided an extremely good input switching type that is improved to simply and reliably prevent the generation of switching noise and to prevent the generation of error current of the current source. It becomes possible to provide electronic switch circuits.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a conventional input switching type electronic switch circuit, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, and FIG. 3 is an example of an electronic switch circuit according to the present invention. The configuration diagram shown in FIG. 4 is a configuration diagram similarly showing another embodiment. Q11-Q16, Q21-Q26, Q31, Q
32...Transistor, A, B...Signal source, VA,
VB…bias power supply, OUT…output terminal, CA, CB
...Capacitor, Ra, RB...Resistor, I1, I2... Constant current source, X, Y... Switching voltage supply terminal.

Claims (1)

[Scope of Claims] 1. First and second transistors whose emitters are commonly connected to a first power source and whose bases are commonly connected to form a current mirror circuit, and whose collectors are the first and second transistors. an input transistor connected to the base of the input transistor and the collector of the second transistor; a time constant circuit inserted between the base of the input transistor and a signal source that supplies the input signal; a switching transistor whose collector is connected to its emitter and to which a switching signal is applied from the outside to its base; and a compensation current equal to the current flowing when the input transistor is in the on state, and which is connected to the time constant circuit when the input transistor is in the off state. a compensating transistor circuit inserted between the emitter of the switching transistor and the second power source in order to cause the current to flow relative to the switching transistor; and a compensation transistor circuit inserted between the emitter of the switching transistor and the second power source to a current source that commonly flows current through the input transistor and the compensation transistor circuit; and an output transistor whose emitter is commonly connected to the input transistor and whose base and collector are connected to the collector of the first transistor. and a first compensation transistor whose collector is connected to the first power supply and whose base is commonly connected to the base of the input transistor; and the collector is connected to the first power supply. a second compensation transistor connected to the emitter of the compensation transistor, a base connected to the second power supply via a bias power supply, and an emitter connected to the emitter of the switching transistor and the current source; , a third compensation whose collector is connected to the first power supply, whose base is commonly connected to the base of the second compensation transistor, and whose emitter is connected to the emitter of the switching transistor and the current source. an electronic switch circuit, comprising: a transistor for output, and extracts an output from a collector of the transistor for output.