JPS63266922A - Multiplexer circuit - Google Patents

Abstract

PURPOSE:To obtain a stable output against a change in the temperature and in the component characteristic by adopting the same circuit constitution relating to a constant current source of the operating side of an analog switch circuit and the constant current source of a buffer amplifier circuit so as to facilitate the design. CONSTITUTION:The buffer amplifier circuit consists of transistors(TRs) Q10, Q13, Q14 and resistors R10, R11, R12 and the constant current source of the TR Q10 consists of the TRs Q13, Q14 and the resistors R10, R11, R12 in a multiplexer circuit. The constant current source is provided so as to be of the same constitution as the constant current source is at the operating side of an analog switch circuit. Since the circuit is constituted as above, a current flowing to the TR Q9 and a current flowing to the TR Q10 are always in the same relation even if the temperature change or component characteristic varies or even if a clamp voltage is changed. Thus, the design of the constant current source is facilitated and a stable output is obtained against the temperature change and deterioration in the component characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multiplexer circuit used as an input circuit for an A/D converter or the like.

[Conventional technology]

FIG. 2 is a circuit diagram showing a conventional multiplexer circuit. In FIG. 0, 1 is a clamp voltage input terminal, and 2.3 is an analog signal 1.3, respectively. II is an input analog signal input terminal, 4 and 5 are analog switch circuit control l
1 signal input terminal, one of which is connected to the power supply and the other to ground. 6 is the output terminal, 7 is the power terminal, 9
．． 10 is a clamp circuit, Q1 to Q12 are transistors,
R1-R9 are resistors, CI and C2 are capacitors, and transistors Q1-Q9 and resistors R1-R6 form a clamp circuit 9. Analog signal clamped to lO! , ■
An analog switch circuit is configured to select one of the transistors Q3. Q4.
Clamp circuit 9 consisting of Q8 and resistors R4, R5°R6
a constant current source connected to transistor Q5. Q6. Q
7 and resistors R1, R2, and R3.
and a constant current source connected to. Further, the transistor QIO-Q12 and the resistors R7 to R9 constitute a buffer amplifier circuit that amplifies and outputs the output of the analog switch circuit.

Next, the operation will be explained.

Analog signal 1 inputted from analog signal input terminals 2 and 3. If is clamped by the clamp circuits 9 and 10 to the clamp voltage applied from the clamp voltage input terminal 1, one of them is selected by the analog switch circuit and output from the buffer amplifier circuit. here,
Assuming that the control signal input terminal 4 is connected to the ground and the terminal 5 is connected to the power supply, the transistor Q7 is turned off, the transistor Q8 is turned on, and the transistors Q1 to Q4゜Q9
A feedback type differential amplifier consisting of transistors Q3. The signal passes through Q4 and Q9, is input to the base of the buffer transistor QIO, is level-shifted, and is output to the output terminal 6.

[Problem that the invention seeks to solve]

Conventional multiplexer circuits require transistors Q3, C4, Q9 and Q10 to match the analog signal to the input range of the A/D converter, requiring the DC level of the clamped signal to be the same when switched.
(7) V st must be the same. Since transistors Q3 and C4 are differential amplifiers (feedback type), the offset of VIE will be small, but transistor Q9
The offset of vlK of QIO and QIO must be matched by a constant current source consisting of resistors R7 to R9 and transistors Q11 to Q12. In such a case, under certain conditions, it is possible to design a constant current source to reduce the offset between V The problem was that the design was extremely difficult when considering various conditions such as changes.

The present invention was made to solve the above-mentioned problems, and it is possible to easily design a constant current source for a buffer amplifier circuit, and it is possible to easily design a constant current source for a buffer amplifier circuit.

The purpose of the present invention is to obtain a multiplexer circuit that can obtain a stable output against changes in element characteristics.

[Means for solving problems]

In the multiplexer circuit according to the present invention, the constant current source of the buffer amplifier circuit is provided to have the same circuit configuration as the constant current source on the operating side of the analog switch circuit.

[Effect]

In this invention, since the constant current source of the buffer amplifier circuit is provided to have the same circuit configuration as the constant current source on the operating side of the analog switch circuit, the constant current source of the buffer amplifier circuit can be easily designed. At the same time, it is possible to reduce drift due to changes in temperature and changes in element characteristics.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a multiplexer circuit according to an embodiment of the present invention. In FIG. 0, the same reference numerals as in FIG. Q14 is a transistor, RI
O-R12 shows resistance.

In this embodiment, transistors QIO, Q13 . Q14 and resistors RIO, R11, and R12 constitute a buffer amplifier circuit, and transistors Q13゜Q14 and resistors R
IO, R11, and R12 constitute a constant current source of the transistor QIO, and this is provided to have the same configuration as the constant current source of the analog switch circuit. That is,
The transistor Q13 has a collector connected to the emitter of the emitter follower transistor QIO and a base connected to the clamp voltage input terminal 1. The emitter of the transistor Q14 is grounded, the collector is connected to the emitter of the transistor Q13 via a resistor, and the base is connected to the emitter of the transistor Q13 via a resistor. It is grounded and connected to the power supply via a resistor.

In a multiplexer circuit with such a configuration, the constant current source of the buffer amplifier circuit has the same circuit configuration as the constant current source on the operating side of the analog switch circuit, so the current flowing through transistor Q9 and the current flowing through transistor QIO are , even if there are temperature changes, changes in element characteristics, etc., or even if the clamp voltage changes, the current will always flow in the same relationship. Therefore, the constant current source of the buffer amplifier circuit can be easily designed, and the
It is possible to obtain stable output against changes in element characteristics.

Note that the present invention can be similarly applied to a multiplexer circuit including an analog switch circuit having a constant current source with another circuit configuration.

〔Effect of the invention〕

As described above, according to the multiplexer circuit of the present invention, the constant current source of the buffer amplifier circuit is provided to have the same circuit configuration as the constant current source on the operating side of the analog switch circuit. The present invention has the advantage that the design can be easily carried out, and a stable output can be obtained against changes in temperature and changes in element characteristics.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a multiplexer circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional multiplexer circuit. In the figure, 1 is a clamp voltage input terminal, 2.3 is an analog signal input terminal, 4.5 is a control signal input terminal, 6 is an output terminal, 7 is a power supply terminal, 9 and 10 are clamp circuits, and Q1
~Q14 is a transistor, and R1-R12 are resistors. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A plurality of clamp circuits each clamping a plurality of analog signals to a predetermined clamp voltage, and a plurality of constant current sources connected to each of the clamp circuits, and one of the constant current sources and an analog switch circuit that selects one of the plurality of clamped analog signals, an output transistor, and a constant current source to the output transistor, and amplifies and outputs the output of the analog switch circuit. A multiplexer circuit comprising a buffer amplifier circuit, wherein a constant current source of the buffer amplifier circuit has the same circuit configuration as a constant current source on the operating side of the analog switch circuit. (2) The analog switch circuit includes a differential transistor circuit in which a first transistor whose base is connected to the clamp circuit, a second transistor whose base and collector are connected, and whose emitters are commonly connected; is grounded via a resistor, is connected to the operation control signal input terminal of the analog switch circuit via the resistor, and has a common-emitter transistor whose collector is connected to the emitter of the differential transistor circuit via the resistor. a plurality of constant current sources, the collectors of the first transistors of the plurality of constant current sources are commonly connected to the power supply via a load transistor, and the collectors of the second transistors of the plurality of constant current sources are connected in common to the power supply via a load transistor. Commonly connected to a power supply via a diode-connected transistor and a load transistor, the buffer amplifier circuit includes an emitter follower transistor whose base is connected to the base of the diode-connected transistor and whose collector is connected to the power supply; is connected to a clamp voltage, the collector is connected to the emitter of the emitter follower transistor, the collector is connected to the emitter of the third transistor through a resistor, the base is grounded through the resistor, and 2. The multiplexer circuit according to claim 1, further comprising a constant current source comprising a common emitter transistor connected to a power source via a resistor.