JPH03214922A - Switching circuit - Google Patents

Abstract

PURPOSE:To realize a high speed switching circuit of unsaturation type capable of outputting n pcs. of input signals selectively, and whose frequency characteristic covers a wide band and is very stable by connecting a diode between an output terminal and each emitter of n-set of emitter follower transistors(TRs), and applying a prescribed bias voltage to n-set of control terminals. CONSTITUTION:A signal inputted to an input terminal 10 is outputted from an output terminal 20 via an emitter follower TR 1 and a diode 7. Since a switching TR 5 and a diode 8 are turned off in this case, a signal inputted to an input terminal 11 is cut off and not outputted to the output terminal 20. When a positive switching pulse is supplied to a control terminal 14 and a negative switching pulse is supplied to a control terminal 13, TRs 5, 2 and the diode 8 being components of a 2nd circuit block are turned on, and TRs 4, 1 and a diode 7 being components of a 1st circuit block are turned off, and a signal inputted to the input terminal 11 is outputted to the output terminal 20.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a switching circuit that extracts an arbitrary signal from two or more types of input signals.

Conventional Technology Figure 3 shows an example of a conventional switching circuit (analog switch) that switches input signals (analog signals) consisting of two or more types using a control signal (pulse signal) and extracts an arbitrary signal.
The explanation will be based on the circuit diagram shown in the figure. The circuit shown in FIG. 3 is a non-saturation type high-speed switching circuit that switches between two types of analog signals.

A conventional switching circuit is an NPN circuit that forms a differential excitation amplifier in which an input signal is input from an input terminal 1O to one side, and an output signal is fed back and input from an output terminal 20 to the other side.
transistors 25 and 26, and PNP transistors 21 . 22, and the collector is an NPN transistor 25. A first circuit block consisting of a switching transistor 4 connected to the common connection point of the 26 emitters and whose base is connected to the control terminal 13 is arranged, and an input signal is input from the input terminal 1l to one side, and the other side is connected to the common connection point of the 26 emitters. NPN transistor 27 forming a differential amplifier to which the output signal is fed back and input from the output terminal 2o.
．． 28, and a PNP transistor 23, which forms a current mirror circuit and serves as an active load of this differential amplifier.
24, collector is NPN } transistor 27.28
A second circuit block consisting of a switch transistor 5 connected to the common connection point of the emitters of the switch transistor 5 and whose pace is connected to the control terminal l4 is arranged.
．． The emitters of the transistors 29 are commonly connected to the first current source 30, and the bases of the transistors 29 whose emitters are connected to the second current source 30 form a current mirror circuit.
P } The collectors of the transistors 22' and 24 are connected in common, and the output signal is obtained at the output terminal 20 by an emitter follower formed by a transistor 29.

Control terminal 13. A switching signal with inverted polarity is input to 14, one of the control terminals is fixed to an appropriate DC bias, and the switching signal is input to the other control terminal. In FIG. 3, 18. 19 indicates a power terminal.

The operation of the conventional switching circuit will be explained below.

If the positive switching pulse is applied to the control terminal l3 as shown in FIG.
When a pulse with an opposite phase is input to the control IMi'J terminal 14, the transistor 4 is turned on (ON) and the transistor 5 is turned off (OFF). On the other hand, analog signals are input to input terminals 10.11. Transistor 5 is O
Since the transistors 23, 24, 27, and 28 forming the second circuit block are OFF, basically the transistors 21, 27, and 28 forming the first circuit block are OFF.
22 , 25 , 26 , 29 . 4 and operates as a buffer amplifier with a gain of 1 times, and only the analog signal input to the input terminal IO is taken out to the output terminal 20.

Problems to be Solved by the Invention Now, in the case of the conventional switching circuit described above, the frequency characteristic between input and output is PNP } transistors 21 and 22 or PNP
Transistor 23. It depends on the performance of the current mirror circuit composed of 24, and is usually a monolithic IC.
Compared to an NPN transistor, for example, in the case of a PNP transistor having a lateral structure, the transient frequency /T is much smaller, so the deterioration of the frequency characteristics described above is significant. This switching circuit also includes transistors 22 . Since the circuit configuration is such that the output signal from 24 is received by transistor 29 forming an emitter follower and fed back to transistors 26 and 28 on one side of the differential amplifier, oscillation is likely to occur due to the phase shift that occurs in this system. unstable. Therefore, conventional switching circuits are not suitable for switching circuits that require a wide band.

The present invention is intended to solve the above-mentioned problems, and aims to provide a non-saturated high-speed switching circuit with wide frequency characteristics and very stable frequency characteristics.

Means for Solving the Problems In order to solve the above problems, the switching circuit of the present invention includes an emitter follower transistor whose base is connected to an input terminal to form an emitter follower, and whose collector is connected to the emitter of the emitter follower transistor. , n circuit blocks (n is an integer of 2 or more) each consisting of a switching transistor whose base is connected to a control terminal are arranged,
The emitters of the n switch transistors are all connected in common, and a first current source is connected between this common connection point and the first voltage terminal, and the output terminal and the n emitter follower transistors are connected to each other. By connecting diodes conductively between the respective emitters, connecting a second WL current source between the output terminal and the second power supply terminal, and applying a predetermined bias voltage to the n control terminals, the n The input signal is selected and outputted to the output terminal.

[4] With the above configuration, the input signal of the circuit block to which a predetermined bias voltage is input to the control terminal is selected and output to the output terminal. In addition, the 1D configuration of the switching circuit of the present invention does not include a feedback circuit like conventional circuits, and the frequency characteristics of the active load do not depend significantly on the frequency characteristic between input and output. The input/output frequency characteristics are widened, and unstable circuit phenomena such as oscillation caused by the circuit configuration are also eliminated.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings. Note that the same components as those in FIG. 3 of the conventional example are given the same reference numerals and explanations are omitted.

FIG. 1 is a circuit diagram of a switching circuit showing one embodiment of the present invention.

The switching circuit of the present invention is an NPN for emitter follower whose base is connected to the input terminal 10 to form an emitter follower.
A first circuit block consisting of a transistor 1 and a switching NPN transistor 4 whose collector is connected to the emitter of the NPN transistor 1 and whose base is connected to the control terminal 13 is arranged, and further whose base is connected to the input terminal 1.
an emitter follower NPN transistor 2 connected to
NPN for the switch connected to the emitter of the transistor 2 and whose base is connected to the control terminal ]4 } A second circuit block consisting of the transistor 5 is arranged, and the NPN for the switch is connected to the control terminal
The emitters of the PN transistors 4 and 5 are commonly connected, and a first current source 1 is connected between this common connection point and the first power supply terminal l9.
, 7, and output terminal 20 and NP for emitter follower.
N } A second 1! for connecting diodes 7 and 8 conductively between the emitters of transistors 1 and 2, respectively, and connecting diodes 7 and 8 conductively between output terminal 20 and second power supply terminal 18. It is constructed by connecting the flow #16.

The operation of the switching circuit having the above configuration will be explained below.

For example, input terminal 10. It is assumed that an analog signal is always input to the control terminal 11, and that a positive polarity switching pulse and a negative polarity switching pulse are simultaneously input to the control terminal 13 and the control terminal 14, respectively. At this time, the transistor 4.1 and the diode 7 forming the first circuit block are ONt.
,,transistor 5.2 forming the second circuit block
and diode 8 is OFF t, second current source 16
The current 16 flows through the diode 7 as part of the collector current of the switching transistor 4. 1st
It is assumed that the current tty of the current WA17 is selected to be an optimal value that normally satisfies 11F>111.

Now, the signal input to the input terminal IO is a transistor for a follower! and is outputted from the output terminal 20 via the diode 7. At this time, since the switching transistor 5 and the diode 8 are OFF, the signal input to the input terminal 11 is blocked and is not output to the output terminal 20.

Further, when a positive polarity switching pulse is applied to the control terminal l4 and a negative polarity switching pulse is applied to the control terminal l3, the transistor 5.2 and the diode 8 which form the second circuit block are turned on, and the first circuit block is formed. When the transistors 4 and 1 and the diode 7 are turned off, the signal input to the input terminal 11 is output to the output terminal 20. As for the diode 7.8, similar switching characteristics can be obtained even if the diode characteristics between the base and emitter of the transistor are used.

In this type of switching circuit, the signal path does not include a feedback circuit like conventional circuits, so the circuit is extremely stable without any oscillation phenomenon, and since it is an emitter follower type circuit, the collector Not only is there less deterioration of the frequency characteristics due to loads and parasitic capacitance, but the input/output frequency characteristics can be improved from It is possible to widen the bandwidth. Furthermore, the number of circuit elements is very small, making it extremely effective when used as a semiconductor integrated circuit. Furthermore, the voltage error between input and output is very small, the temperature characteristics at the output terminal 20 can be almost ignored, the input impedance is large because it is an emitter follower type circuit, and the output impedance is also large when the impedance conversion circuit is connected to the output terminal 20. It can easily be made sufficiently small by adding .

FIG. 2 shows a switching circuit for three or more input signals. The switching operation is similar to the switching circuit shown in Fig. 1, but
Emitter follower transistors that form a circuit block as many as the number of input signals. Finally, a circuit consisting of a switching transistor and a diode is placed in parallel.

For example, when extracting a signal input to the input terminal 12, by turning on only the switching transistor 6, the signal can be outputted to the output terminal 20 via the diode 9.

Although the embodiments shown in FIGS. 1 and 2 are constructed using NPN transistors, it is also possible to construct a switching circuit that can perform the same switching operation as in the embodiments using PNP transistors. It is possible.

Effects of the Invention As described above, according to the present invention, a predetermined bias voltage can be obtained by selecting the input signal of a circuit block inputted to the control terminal as the output terminal, and the feedback circuit like the conventional circuit can be obtained. Since the frequency characteristics between input and output do not depend significantly on the frequency characteristics of the active load, it is possible to obtain stable circuit characteristics over a wide band and without oscillation phenomena. In addition, the voltage error between input and output is very small, the temperature characteristics at the output terminal can be ignored, the mother input impedance is large because it is an emitter follower type circuit, and the output impedance is also large due to the emitter follower type circuit type. It can be easily made sufficiently small by adding it to the output terminal.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a switching circuit showing one embodiment of the present invention, Fig. 2 is a circuit diagram of a switching circuit showing another embodiment of the invention, and Fig. 3 is a circuit diagram of a conventional switching circuit. . 1, 2.3... NPN transistor for emitter follower, 4, 5.6... NPN transistor for switch, ? , 8.9...diode, 10 , 11 .
12...Input terminal, 13, 14, Is...
Control terminal, 16. 17... Current source, 18. 1
9...Power terminal, 20...Output terminal.

Claims (1)

[Claims] 1. A circuit block consisting of an emitter follower transistor whose base is connected to an input terminal to form an emitter follower, and a switch transistor whose collector is connected to the emitter of the emitter follower transistor and whose base is connected to a control terminal. n switch transistors (n is an integer of 2 or more), the emitters of the n switch transistors are all connected in common, and a first current source is connected between this common connection point and the first power supply terminal, and an output A diode is conductively connected between the terminal and the emitters of the n emitter follower transistors, a second current source is connected between the output terminal and the second power supply terminal, and a predetermined current source is connected to the n control terminals. A switching circuit characterized in that the n input signals are selected and outputted to the output terminal by applying a bias voltage.