JPH01264405A - Switching circuit - Google Patents

Abstract

PURPOSE:To simplify the constitution of the title circuit so as to make the circuit into an IC and to reduce the current consumed by the circuit by providing a switching circuit which switches a circuit composed of a 1st signal source and a 1st amplifier to another circuit composed of a 2nd signal source and a 2nd amplifier, or vice versa. CONSTITUTION:When a switching circuit 18 is set to an amplifier 14 side, a supply voltage Vcc is impressed across the amplifier 14 and, at the same time, a constant- current source 19 is driven, resulting in the driven state of the amplifier 14. Then the output signal of a signal source 13 is outputted from a terminal 17 after amplification 14. It the grounding current amplification factors of emitter-grounded transistors(TR) Q1-Q3 is beta, an electric current of I1/2beta is made to flow to the base of the TR Q2 which is the negative input terminal of the amplifier 14 and an offset of R1I1/2beta is produced as compared with the DC potential at an output terminal. When the circuit 18 is set to another amplifier 12 side, on the other hand, another constant-current source 20 is driven and the output signal of another signal source 11 is outputted from the terminal 17. In this case, an electric current of I1/2beta is made to flow to the base of the TR Q3 and the DC potential at the negative input terminal of the amplifier 14 offsets by R1I1/2beta as compared with the DC potential at the output terminal.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to selectively switching the outputs of a plurality of amplifier circuits with different gains, frequency characteristics, etc., such as preamplifiers, etc. The present invention relates to a switching circuit, and particularly to a switching circuit suitable for integration into an IC (integrated circuit).

(Prior Art) As is well known, switching circuits that selectively switch the outputs of multiple amplifier circuits with different gains, frequency characteristics, etc.
It is constructed as shown in FIG. That is, the output signal from the first signal source 11 is supplied to the input terminal via the coupling capacitor CI, and the output signal from the second signal source 13 is coupled. The second voltage supplied to the positive input terminal via capacitor C2
The output of the amplifier 14 is selectively switched by a switch circuit 15 to be outputted to an amplifier 16 from an output terminal 17. Note that a resistor R1 is interposed and connected between the negative input terminal 1 and the output terminal of the second amplifier 14, and the negative input terminal 1 is grounded through a resistor R2 and a capacitor C3 in series.

In other words, signals with different levels are level-matched by the first amplifier 12 and the second amplifier 14 with equal levels and frequency characteristics, and are then led to the next stage circuit. The second amplifiers 12 and 14 can both be operated at all times, and if the output DC voltages of the first and second amplifiers 12 and 14 are made equal, the amplifiers 12 and 14 can be used as amplifiers when switching the switch circuit 15. 16
DC fluctuations in the output voltage can also be eliminated.

However, in the conventional switching circuit as described above, the IC
In this case, the problem arises that it is difficult to circuitize the switch circuit 15 and the number of elements increases.

Furthermore, keeping both the first and second amplifiers 12, 14 in constant operation also results in an unnecessary increase in current consumption.

(Problems to be Solved by the Invention) As described above, the conventional switching circuit has the problems that it is difficult to integrate it into an IC and the current consumption increases.

Therefore, the present invention was made in consideration of the above circumstances, and an object thereof is to provide an extremely good switching circuit that has a simple configuration, is suitable for IC implementation, has low current consumption, and has no problems with transient characteristics during switching. shall be.

[Configuration of the Invention (Means for Solving the Problems) This invention comprises a first amplifying means that supplies a signal from a first signal source, a base that supplies a signal from a second signal source, and a base that supplies a signal from a second signal source. a first transistor serving as an input terminal; a second transistor having its emitter commonly connected to the first transistor and having its base serving as a negative input terminal; a first constant current source that supplies a constant current to a common emitter connection point of the second transistor; a third transistor whose bases are commonly connected to the second transistor; a second amplifying means, which includes a second constant current source in the input stage that supplies a current that is 1/2 of the output current of the constant current source, and whose output end is commonly connected to the output end of the first amplifying means; A first resistor is connected in series between the output terminal of the second amplifying means and the negative input terminal, and a reference potential point is connected between the negative input terminal of the second amplifying means and the reference potential point. A power source voltage is applied to the inserted second resistor and capacitor, and the second amplifying means, and the first constant current source is activated to enable the second amplifying means to perform a signal amplification operation. a second driving means for applying a power supply voltage to the first driving means and the first amplifying means to enable the first amplifying means to perform a signal amplification operation, and for activating a second constant current source; and is configured to set the output DC potentials of the first and second amplification means to be equal.

(Function) According to the above-mentioned configuration, firstly, the conventional switch circuit for switching the signal system is not required, so the configuration can be simplified, and the use of IC can be effectively promoted. can. Furthermore, since the power supply voltage is selectively applied to the first and second amplifying means, current consumption can be reduced. Furthermore, since the second amplifying means maintains a constant DC voltage at its negative input terminal regardless of whether it is in an operating state or a non-operating state, its transient characteristics at the time of switching are also good.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 3 are indicated by the same symbols, and only the different parts will be described here. That is, the first amplifier 12 and the second amplifier 1
4, the switch circuit 18 selectively applies the electric J1λ voltage Vce to the first and second amplifiers 12 and 14.
is operated selectively. Here, the output DC potentials of the first and second amplifiers 12 and 14 are set to be equal. Further, the output terminals of the first and second amplifiers 12 and 14 are commonly connected, and the connection point thereof is directly connected to the output terminal 17.

Here, the input stage of the second amplifier 14 has a circuit configuration shown in FIG. ], the positive input terminal + is N
It is connected to the base of a PN type transistor Ql.

Further, the negative input terminal 1 is connected to another NPN type transistor Q2.
．． Each is connected to the base of Q3. The emitters of the transistors Ql and Q2 are commonly connected, and the connection point thereof is grounded via a constant current source 19. Furthermore, the emitter of transistor Q3 is grounded via constant current source 20.

Note that the collectors of the transistors Ql and Q2 are each connected to an unillustrated amplifier circuit driven by the power supply voltage Vce for amplifying the signal supplied to the positive input terminal +. In addition, the collector of transistor Q3 has
A predetermined DC bias is applied.

Here, the constant current source 9 is driven with the switch circuit 18 switched to the second amplifier 14 side, and generates a constant current of 11. In addition, "two-legged constant current source 2
0 is driven with the two-legged switch circuit j8 switched to the first amplifier 12 side, and generates a current that is 1/2 of the output current 1 of the constant current source 19.

The operation of the above configuration will be described below. First, when the switch circuit 18 is switched to the second amplifier 14 side, the power supply voltage Vcc is applied to the second amplifier 14, the constant current source 19 is driven, and the second amplifier 14 is brought into a driving state. . Therefore, the output signal from the second signal source 13 is amplified by the second amplification: (=14) and is led out to the output terminal 17.

In this case, assuming that the common emitter current amplification factor of the transistors Q1 to Q3 is β, a current of If/2β flows in the negative input terminal of the second amplifier 14, that is, the base of the transistor Q2 in a direct current manner. Therefore, the DC potential at the negative input terminal of the second amplifier 14 has an offset of R11l/2β compared to the DC potential at the output terminal.

On the other hand, when the switch circuit 18 is switched to the first amplifier 2 side, the power supply voltage VCC is applied to the first amplifier 12,
The first amplifier 12 is brought into a driving state, and the constant current source 20 is driven. Therefore, the output signal from the first signal source 11 is amplified by the first amplifier 12 and output to the output terminal 17.

In this case, since the constant current source 20 is in the driving state, a current of 11/2β flows in the base of the transistor Q3 in terms of direct current. Therefore, the DC potential at the negative input terminal of the second amplifier 14 produces an offset of R11l/2β compared to the DC potential at the output terminal.

Therefore, according to the configuration as in the above embodiment, first,
Since the conventional switch circuit 15 for switching the signal system is not required, the configuration can be simplified and the use of IC can be effectively promoted. Furthermore, since the power supply voltage Vcc is selectively applied to the first and second amplifiers 12 and 14, current consumption can be reduced. Furthermore, since the DC voltage at the negative input terminal of the second amplifier 14 is held constant regardless of the operating state or non-operating state, the capacitor C3 is not charged or discharged even if the switch circuit 18 is switched. Therefore, transient characteristics at the time of switching can be improved.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effect of the invention] As detailed above, according to this invention, I
It is possible to provide an extremely good switching circuit that is suitable for C conversion, has low current consumption, and has no problems with transient characteristics during switching.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing the main part of the same embodiment, and FIG. 3 is a block circuit diagram showing a conventional switching circuit. be. 11... First signal source, 12... First amplifier, 1
3... Second signal source, 14... Second amplifier, 15
...Switch circuit, 16...Amplifier, 17...Output terminal, 18...Switch circuit, 19.20...Constant current source. Applicant's agent Patent attorney Takehiko Suzue-''S2 figure

Claims (1)

[Claims] first amplification means for providing a signal from a first signal source;
a first transistor whose base is supplied with a signal from a second signal source and whose positive input terminal is a positive input terminal; a second transistor whose emitter is commonly connected to the first transistor and whose base is a negative input terminal; 1. A first constant current source that supplies a constant current to a common connection point of the emitters of the second transistor; a third transistor whose bases are commonly connected to the second transistor; a second constant current source that supplies a current that is 1/2 of the output current of the first constant current source at the input stage, and whose output terminal is commonly connected to the output terminal of the first amplifying means; a first resistor interposed and connected between the output end of the second amplification means and the negative input end; and a first resistor connected between the negative input end of the second amplification means and the reference potential point. Signal amplification by the second amplification means by applying a power supply voltage to the second amplification means and a second resistor and capacitor interposed and connected in series therebetween, and with the first constant current source in operation. A power supply voltage is applied to a first driving means that enables operation, and a power supply voltage is applied to the first amplifying means to enable the first amplifying means to perform a signal amplification operation, and the second constant current source is brought into an operating state. 1. A switching circuit comprising: a second driving means, wherein the output DC potentials of the first and second amplifying means are set to be equal.