JPS58159024A - Wide band signal switching circuit - Google Patents

Abstract

PURPOSE:To improve a crosstalk characteristic in case when a signal is cut off and also power consumption in that case, by using a field effect transistor in a wide band emitter-follower type switching circuit of or a switching circuit using a diode. CONSTITUTION:When a controlling transistor 5 is turned on by controlling a base current of the transistor 5 by the potential of a control terminal 6, a current flows to a resistance 9, and the gate-source voltage of a field effect transistor (FET) 15 is set to reverse bias voltage by a voltage drop generated in the resistance 9. Accordingly, the FET15 becomes a cut-off state, and the current flowing in the resistance 9 becomes a bias current of the emitter of a transistor (TR) 3 and the base of a TR4. As a result, emitter-follower circuits of 2 stages are operated, and a signal is outputted to an output terminal 2. When the TR5 is turned off from the control terminal 6, the FET15 attains to a conducting state, the potential of a connecting point 10 attains the same potential as that of an electric power source terminal 7, and the base-emitter potential of the TR3 and 4 is biased in the reverse direction. Also, the connecting point 10 is grounded in AC.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the characteristics of a wideband signal switching circuit.

Conventionally, wideband signal switch circuits include switches that conduct or cut off the forward current of a diode and utilize the difference in impedance of the diode in those cases, and switches that connect the collector and emitter when the base of a transistor is forward biased or reverse biased. There are switches that utilize conduction/cutoff of the transistor, and switches that function as a switch by fully controlling the bias voltage of a transistor operated as an emitter follower. This emitter follower type switch has the function of a buffer amplifier and also has good broadband characteristics. FIG. 1 shows an example of this emitter follower type switch circuit, in which 101 and 102 surrounded by broken lines each constitute one switch. Here, 1 is a signal input terminal, 2 is a signal output terminal, a control terminal for the six switch, 7 is a power supply terminal to which a positive voltage is applied, and 8 is a power supply terminal to which a negative voltage is applied. In this example, it is 2-man power and 1 output (hereinafter, a switch with 1 input and m output will be expressed as nxm), but if you want to use 1 x 1 switch, prepare n switches and use the power terminal 7. , 8 and the output terminal 2, and insert a resistor 201 between the output terminal 2 and the positive power supply terminal 7. Furthermore, when using an nxm switch, the n
-m switch 8i) (1it 4n, 1gi 5) 4m)
, connect the input terminals 1 of the switches with the same t, connect the output terminals 2 of the switches with the same t, and connect the resistor 201 to each output terminal in the same way as in the case of 7LX1. Bye. The transistors 3 to 4 that operate as emitter followers in each switch conduct the control transistor 5 with the voltage applied to the control terminal 6, and apply an appropriate bias through the resistor 9, resulting in the signal being input to the signal input terminal 1. The signal appears at the signal output terminal 2. Also, when the voltage at the control terminal 6 is changed to turn off the transistor 5, no current flows through the resistor 9, and the potential at the connection point 10 between the emitter of the transistor 3 and the base of the transistor 4 is brought to the same level as the positive power supply terminal 7 by the resistor 11. potential, and the base-emitter of the transistor 3.4 is reverse biased. Therefore, the transistor 3.4 tends to operate as an emitter follower, and almost no signal is transmitted. This circuit has the characteristic that there is almost no current consumption when the signal is cut off, but in order to prevent an increase in current consumption when the signal is on, a relatively large value is used for the resistor 11, so that the The signal leaked by the capacitance is hardly attenuated and leaks again to the output terminal 2 due to the capacitance between the base and emitter of the transistor 4, making it impossible to obtain sufficient crosstalk characteristics.In order to improve the crosstalk characteristics, the control Eliminate transistor 5 and replace transistor 3.4
Japanese Patent Publication No. 13708/1983 shows a switch circuit in which the resistor 11 for reverse biasing the oscilloscope is replaced with a new control transistor 13 as shown in FIG. In the circuit shown in FIG. 2, the transistors 3 and 4 are reverse-biased by the transistor 13 when the signal is cut off, and at the same time, the connection point 1o between them is grounded in an alternating current manner to improve crosstalk characteristics. However, even when the signal is cut off, there is a drawback that the base current flowing through the resistor 14 for turning on the transistor 13 and the collector current of the transistor 13 passing through the resistor 9 are consumed. These two circuits improve crosstalk characteristics,
As a way to reduce current consumption when the signal is cut off, a circuit in which the resistor 9 shown in FIG. 2 is replaced with a circuit in which the resistor 9 and the transistor 5 are connected in series as shown in FIG. 1 can be considered. A new circuit is required to control both at the same time, making the circuit considerably more complex. Furthermore, there is a drawback that the base current of the transistor 130 is consumed even when the signal is cut off.

An object of the present invention is to use a field effect transistor in a broadband emitter follower type switch circuit or a switch circuit using a diode as described above, to have good crosstalk characteristics when a signal is cut off, and to reduce current consumption at that time to almost zero. The purpose of the present invention is to provide a circuit configuration that achieves this.

An embodiment of the present invention will be described below with reference to FIG. 1 is a signal input terminal, 2 is a signal output terminal, 3.4 is a transistor for emitter follower operation, 6 is a control terminal, and the bias of transistors 3 and 4 is controlled by transistor 5. The collector of transistor 5 is resistor 9
through the emitter of transistor 3 and the base of transistor 4 and the field effect transistor (FET) 15
is connected to the source at connection point 10. FET 15
Its drain is connected to a power supply terminal 7 to which a positive voltage is applied, and its gate is connected to the collector of the transistor 5 via a resistor 16. A positive power supply is connected to the collector of transistor 3, and the emitter of transistor 5 and transistor 4 are connected to each other.
A negative power supply is supplied to the collector of .

When the base current of the control transistor 5 is controlled by the potential of the control terminal 6 and the transistor 5 is turned on, a current flows through the resistor 9, and the voltage drop generated across the resistor 9 becomes the reverse bias voltage between the gate and source of the FET 15. . FET 15 is cut off and the current flowing through resistor 9 becomes a bias current for the emitter of transistor 3 and the base of transistor 4. Therefore, the two-stage emitter follower circuit operates and a signal is output to the output terminal 2. In this case, the minimum value of the input signal voltage is vlNmin, and the voltage between the base and emitter of transistor 3 is V.
3' - The collector saturation voltage of transistor 5 is V. R5s
If the negative voltage applied to the at 1 power supply terminal 8 is vEF, the minimum value of the voltage applied to the resistor 9 "R9m1n" is
■R9min ”” vINmin-VBEa 'C
Essat ”EE, so the absolute value of the gate-source voltage with FET15 cutoff is V
You have to choose a small 9m1n. Note that the resistor 16 is FET1
This is to prevent the frequency characteristics of the switch from deteriorating when the signal is conductive due to the capacitance between the gate and the source being connected in parallel to the resistor 9 that serves as the load of the transistor 3. It can be omitted depending on the purpose.

When the transistor 5 is turned off by the control terminal 6, no current flows through the resistor 9, so the voltage between the gate and the source of the FET 15 becomes zero, and the drain and source of the FET 15 become conductive. Therefore, the potential of the connection point 10 is the same as that of the power supply terminal 7 to which a positive voltage is applied, and the bases and emitters of the transistors 3 and 4 are reverse biased. Further, since the connection point 10 is grounded in an alternating current manner, crosstalk characteristics are improved. It goes without saying that it is better to use an element with a small on-resistance for the FIT 15. Furthermore, since the transistors 3, 4.5 are off in this state, the current consumption when the signal is interrupted is only due to the leakage current of these transistors and is very small. Furthermore, in the circuit configuration shown in Figure 3, a transistor 5 and 1502 FBT semiconductor switching elements are used to control the emitter follower circuit, but the control method seen from the control terminal 6 is exactly the same as that shown in Figure 1. It is easy to control the conduction/cutoff of the switch.

In the example shown in FIG. 3, a case has been described in which two transistors 3 and 4 that operate as emitter followers are used, but if the transistor 3 is replaced with a diode 17 as shown in FIG. When only transistor 4 is replaced with diode 1B as shown in Figure (b), and when transistors 3 and 4 are each replaced with diodes 17 and 18 as shown in Figure (c), the same switching operation occurs. Power consumption when the signal is cut off is almost zero, and good crosstalk characteristics can be obtained. Furthermore, add a PNP transistor to the NPN) transistor.
) It is obvious that a similar effect can be obtained with a circuit in which the N-channel FET is replaced with a P-channel FET in the transistor, and the polarity of the diode and power supply is reversed.

It is also clear that a switch matrix with inputs of 1 and outputs of m can be constructed by using a and ra of the single switches shown in FIGS. 3 and 4 and making the connections described in FIG. 1.

When applied to an exchange that exchanges broadband information, there are far more matrix switches in a signal-blocking state than in a signal-conducting state. Therefore, the present invention can be expected to significantly reduce power consumption by reducing the power consumption during signal interruption to almost zero without deteriorating the crosstalk characteristics, and is also advantageous when implementing high-density packaging such as IC. .

[Brief explanation of the drawing]

1 and 2 are circuit examples of a conventional emitter/7 follower type switch, Figure 3 is an example of an emitter follower type switch circuit for explaining the present invention, and Figure 4 is a circuit example of a diode of the present invention. This is an example of application to a switch circuit using m-. 1...Signal input terminal, 2...
...Signal output terminal, 3.5 ......N
PN) transistor, 4,13...
PNP) transistor, 6... Control terminal, 7... Positive power supply terminal, 8...
...Negative power supply terminal, 9, 11.12.14.16.2
01・・・・・・Resistor, 10・・・・・・・・・
・ Connection point between the emitter of transistor 3 and transistor 40 pace, 15... Junction type N-channel field effect transistor, 17.18...
・・Tiode, 101.102・・・・・・・・・
switch circuit. Patent applicant Nippon Telegraph and Telephone Public Corporation Figure 2 Figure 3 011 -111111--11111-

Claims (2)

[Claims] (1) A first transistor that inputs a signal from its base and outputs it from its emitter, or a diode oriented in the same direction as the base-emitter junction of the transistor (hereinafter, the first transistor and the diode are collectively referred to as "first switch element"). In addition, the base and emitter of the transistor and the corresponding terminals of the diode are collectively referred to as ``base, etc.'' and ``emitter, etc.''), and the output signal from the first switch element is input to the base, and the output signal from the first switch element is input to the base, A second transistor complementary to the first transistor that outputs a signal to the transistor, or 11 diodes that are the same as the junction of the transistor (hereinafter, the second transistor and the diode are collectively referred to as "second switch element"). , 1st
It is connected to the emitter, etc. of the switch element and the base, etc. of the second switch element, and turns on/off the first and second switch elements.
In a switch circuit equipped with a control circuit that turns off,
The control circuit includes a series circuit of a resistor and a third transistor for simultaneously conducting or blocking forward bias currents in the emitter of the first switch element and the base of the second switch element, and the resistor. It is controlled by the applied voltage, and when the third transistor is turned off quickly, the connection points such as the emitter of the first switching element and the base of the second switching element are grounded in an alternating current manner, and 1. A wideband signal switch circuit comprising a field effect transistor for applying a reverse bias voltage between the base, emitter, etc. of the second switch element. (2) A wideband signal switch circuit with the following configuration is
1. A wideband signal switch matrix circuit characterized in that m switches are used to constitute a switch/trix having several inputs and m outputs. A first switch element, a second switch element whose input is the output of the first switch element r, connected to the emitter etc. 7 of the first switch element and the base etc. of the second switch element i, A broadband signal switch circuit comprising a control circuit for turning on/off a first and second switch element, the control circuit comprising: an emitter of the first switch element, etc. and a base of the second switch element; A series circuit of a resistor and a third transistor for simultaneously conducting or cutting off forward bias currents such as An electric field effect for grounding the connection point between the emitter, etc. of the switch element and the base, etc. of the second switch element in an alternating current manner, and applying a reverse bias voltage between the base, etc. and emitter, etc. of the first and second switch elements. A wideband signal switch circuit composed of transistors.