JPH03159311A - Diode switch - Google Patents

Abstract

PURPOSE:To reduce the quantity of output difference generated in on/off time by providing a current source circuit to correct the deviation of timing of two control currents. CONSTITUTION:Transistors 1-3, 4, 5, 15,and 16 constitute first to third current mirror circuits, respectively, and a transistor 14 generates the output current of a second current mirror. Assuming the collector currents of the transistors 3, 5, and 16 as I3, I5, and I16 respectively, a circuit is composed so as to set equation I5=I3+I16. When the diode switch is changed from an on-state on an off-state, the off-time of the current I5 is delayed compared with the current I3, and the DC voltage of an output terminal 12 is lowered excessively, however, since the turn-off of the current I16 is further delayed, it is operated so as to boost the DC voltage. Thereby, the quantity of output DC difference generated due to the deviation of timing of the on/off of the control current can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a diode switch that determines whether or not to transmit a signal by turning on and off a current source.

BACKGROUND OF THE INVENTION In recent years, switching circuits using electronic means have come to be used instead of mechanical switches.

A conventional diode switch will be explained below.

Figure 2 shows a conventional diode switch, 21,2
2.23 is a PNP transistor constituting a current mirror, 24.25 is an NPN transistor constituting a current mirror, 26, 27, 28, and 29 are switch diodes, 30 is a hold capacitor, and 33 is a switch current source. The current of the switch current source 33 flows through the PNP transistors 21 to 23 and the NPN transistors 24 and 25.
The diodes 26 to 29 are controlled by the current output from the current mirror formed by the diodes 26 to 29. At this time, 1 33F I 25= 1 23
......Set a constant so that it becomes +11.

When current 133 flows, current I23=I:! 5 flows through the diodes 26 to 29, and when these diodes are turned on, the signal input from the input terminal 3l is output to the output terminal 32. Next, when current 33 is turned off, I
23=I 25=O, and the diodes 26 to 29 are turned off. That is, the signal at the input terminal 31 is cut off from the output terminal 32 and held by the capacitor 30 .

Problems to be Solved by the Invention However, in the above conventional configuration, the current T33 is turned on and off.
When off, the currents {23 and 125 do not turn on and off at the same time, and the time for the current {25} to turn off is delayed compared to the current I23, so the charge is drawn to the negative side and an output step is created at the output terminal 32. It had some problems.

The present invention solves the above-mentioned conventional problems, and provides a diode switch that can reduce the amount of output DC level difference caused by the difference in the on/off timing of the upper and lower currents I25 and I23 supplied to the diode. It is an object.

Means for Solving the Problem In order to achieve this object, in addition to the first and second current mirrors that drive the switch diode, a second
mirrors the current supplied from the current mirror of the first
The configuration includes a third current mirror that produces a current that is mixed with the current from the current mirror.

Effect: With this structure, it is possible to reduce the amount of output DC step difference that has been generated due to a timing shift between on and off of the control current for turning on and off the switch diode.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a diode switch, which is an embodiment of the present invention. In Figure l, 1-34-5.15-
16 are first, second and third current mirror transistors, 6 to 9 are switch diodes,
10 is a hold capacitor, and 13 is a switch current source. In addition to the conventional structure, it is composed of a transistor 14 which produces the output current of the second current mirror, and transistors 15 and 16 which constitute the third current mirror. The current supplied to the switch diode is the transistor 3,
With a collector current of 5.16, these are I3.15,It
If s, r5= 13+ I+6 (2)
Configure it so that When this diode switch shifts from on to off, the time for the current (1)5 to turn off is delayed compared to the current I3, and the DC voltage at the output terminal 12 drops transiently. D because the current r+6 turns off is further delayed.
It operates to pull up the C voltage, and as a result, output terminal 1
2. The drop in DC voltage can be suppressed.

As described above, according to the present invention, the switch diode can be
By adding a current source circuit for correcting the timing difference between the two control currents to be driven, it is possible to obtain the effect of reducing the amount of output step difference that occurs during on/off. Also, if the same level fluctuation is allowed,
It becomes possible to use a smaller hold capacitor than in the past.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a diode switch according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional diode switch. 1-3, 4-5, ■4-16.21-23.24-25
...transistor that constitutes a current mirror,
6-9.26-29...Switch diode,
10.30...Hold capacitor.

Claims (1)

[Claims] A switch circuit that controls signal transmission by turning on and off a diode bridge includes a first current mirror connected to a switch current source, and a second current mirror that mirrors a current supplied from a first output terminal of the first current mirror. a third current mirror that mirrors the current at the first output end of the second current mirror;
One end is connected to the connection point of the current mirror and the second output end of the first current mirror, and the other end is connected to the second output end of the first current mirror.
and a diode bridge connected to the second output of the current mirror.