JPH0478050B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an analog switch circuit that compensates for characteristic fluctuations due to temperature.

Prior Art and Problems A repeater monitor circuit is provided with an analog switch circuit that selects and monitors one channel out of a plurality of channels. Such an analog switch circuit is required to have good linearity and low power consumption, and in order to meet these demands, the configuration shown in FIG. 1 was previously proposed. In the figure, IN1 and IN2 are analog signal input terminals, CT1 and CT2 are switching control signal input terminals, REF is a comparison reference voltage input terminal, OUT is an output terminal, V _EE is a power supply voltage, and Q1 to Q
3, Q11~Q13, QC0~QC2, Q21~Q
26 is a transistor, and R ₁ to R ₉ and Rw are resistors.

Transistors Q2 and Q12 are npn type, transistors Q3 and Q13 are pnp type, and transistor Q
2, Q3 constitute a composite transistor circuit corresponding to input terminal IN1, and transistors Q12, Q1
3 constitutes a composite transistor circuit corresponding to the input terminal IN2. In addition, transistors QC1 and QC2, whose bases receive switching control signals from input terminals CT1 and CT2, together with transistor QC0, whose bases receive a comparison reference voltage from input terminal REF, form a switching control circuit corresponding to input terminals IN1 and IN2. The transistor Q23 constitutes a common current source. Also, transistor Q25, Q
26 constitutes an output stage.

Although Figure 1 shows the case where two channels of analog signals are switched and output to the output terminal OUT, it is also possible to configure a configuration in which more channels of analog signals are switched and output. In that case as well, only one current source transistor Q23 is required in the switching control circuit.

For example, when a high-level switching control signal is applied to input terminal CT1, transistor QC1 turns on because transistor QC0 and transistors QC1 and QC2 form a differential pair.
Transistors QC2 and QC0 are turned off. Therefore, the composite transistor circuit consisting of transistors Q2 and Q3 becomes operational, and the analog signal applied to the input terminal IN1 is output from the output terminal OUT. Furthermore, since the composite transistor circuit consisting of transistors Q12 and Q13 is in an inactive state, the analog signal applied to the input terminal IN2 is not output.

The current flowing through the transistor Q23 constituting the current source is I ₀ , the current flowing through the transistor QC1 is I ₁ ,
If the current flowing through transistor Q3 is I ₂ , the current flowing through resistor R ₁ is I ₃ , the current flowing through transistor Q25 is I ₄ , and the current flowing through transistor Q26 through resistor Rw is I ₅ , then I ₁ ≒ I ₀ ...(1) I ₂ ≒I ₄ ≒I ₅ ...(2) and the base-emitter voltages of transistors Q1, Q2, Q3 are V _BE1 , V _BE2 , V _BE3 ,
If V _BE ≒V _BE1 ≒V _BE2 ≒V _BE3 , then V _IN1 = −R ₁ I ₃ −V _BE3 +V _BE2 +V _BE1 = −R ₁ I ₃ +V _BE ……(3). Note that V _IN1 is an analog signal applied to the input terminal IN1.

Since the current gain of transistor Q2 is large, I ₂ =I ₃ -I ₁ (4).

The output voltage V _OUT becomes V _OUT =−RwI ₅ (5) due to the current I ₅ flowing to the resistor Rw via the transistor Q26. Therefore, from equations (1) to (5) above, V _OUT = −RwI ₂ = −Rw (I _{3 −} I ₁ ) = −Rw [− (1/R ₁ ) (V _IN1 − V _BE ) − I ₀ ] = (Rw/R ₁ ) V _IN1 + RwI ₀ − (Rw/R ₁ ) V _BE ……(6).

As can be seen from equation (6), the output voltage V _OUT includes a term of the base-emitter voltage V _BE , and this base-emitter voltage V _BE has temperature dependence _. If the temperature coefficient is k [mV/℃], the output voltage V _OUT is (Rw/R ₁ )k [mV/℃].
℃]. That is, the previously proposed analog switch circuit of FIG. 1 has wide linearity and low power consumption, but the npn transistor and pnp transistor of the composite transistor circuit including the input stage transistors Q1 and Q11. Due to the _VBE , the output voltage fluctuates due to temperature fluctuations.

OBJECT OF THE INVENTION The present invention aims to compensate for characteristic fluctuations due to temperature changes while maintaining low power consumption and wide range linearity.

Structure of the Invention The present invention provides an input stage transistor corresponding to the input terminal to which input analog signals from a plurality of input terminals are respectively applied, an npn transistor to the base of which the output of the input stage transistor is applied, and an emitter of the npn transistor. a switching control circuit including a composite transistor circuit corresponding to the input terminal and comprising a pnp transistor connected to a base, and a transistor corresponding to the composite transistor circuit that controls operation and non-operation of the composite transistor circuit according to a switching control signal; , and a common current source for the transistors of this switching control circuit.
A temperature compensation diode is connected in series with the PNP transistor of the composite transistor circuit. Examples will be described in detail below.

Embodiment of the Invention FIG. 2 is a circuit diagram of a main part of an embodiment of the present invention, in which the same reference numerals as in FIG. 1 indicate the same parts, Q4,
Q14 is a diode for temperature compensation. In this embodiment, a diode is formed by connecting the base and collector of an npn transistor, but it is also possible to use a normal diode. This diode is used in a composite transistor circuit.
It is connected to the emitters of pnp transistors Q3 and Q13. If V _BE4 is the voltage between the base and emitter of diode Q4, the above equation (3) is: V _IN1 = −R ₁ I ₃ −V _BE4 −V _BE3 +V _BE2 +V _BE1 = −R ₁ I ₃ ……(7 ), and the output voltage V _OUT is (1), (2), (4), (5), (7)
From the formula, V _OUT = −RwI ₂ = −Rw (I ₃ − I ₁ ) = −Rw [− (V _IN1 / R ₁ ) − I ₀ ] = (Rw / R ₁ ) V _IN1 + RwI ₀ ……(8 ) becomes. That is, since equation (8) does not include the term V _BE , the output voltage V _OUT has no temperature dependence.

A composite transistor circuit whose operation and non-operation are restricted by a switching control circuit, and input terminals IN1 and IN2
It is necessary to connect the input stage transistors Q1 and _Q2 of emitter-follower configuration between the By connecting the diodes Q4 and Q14 to the composite transistor circuit, the output voltage V _OUT becomes independent of temperature.

Effects of the Invention As explained above, the present invention provides input stage transistors Q1 and Q11 to which a plurality of input analog signals are respectively applied, and the input stage transistor Q.
1. A composite transistor circuit consisting of npn transistors Q2, Q12 and pnp transistors Q3, Q13 to which the output of Q11 is applied, and a transistor that controls the operation and non-operation of the composite transistor circuit.
It is equipped with a switching control circuit consisting of QC0, QC1, QC2, etc., and temperature compensation diodes Q4 and Q14 are connected to the composite transistor circuit, so that the output voltage V _OUT output from the output terminal OUT is connected to the base of the transistor. This does not depend on the emitter-to-emitter voltage V _BE , and the output voltage V _OUT remains stable even with temperature fluctuations. Therefore, in an analog switch circuit that selects and outputs one analog signal from a single input analog signal or a plurality of input analog signals, there is an advantage that the output voltage accuracy can be improved.

[Brief explanation of the drawing]

FIG. 1 is a previously proposed analog switch circuit, and FIG. 2 is a circuit diagram of an embodiment of the present invention. IN1 and IN2 are analog signal input terminals, CT
1, CT2 is the input terminal of the switching control signal, REF is the input terminal of the comparison reference voltage, OUT is the output terminal, V _EE is the power supply voltage, Q1 to Q3, Q11 to Q13, QC0
~QC2, Q21~Q26 are transistors, _R1 ~
R ₉ and Rw are resistors, and Q4 to Q14 are diodes for temperature compensation.

Claims (1)

[Claims] 1. An input stage transistor corresponding to the input terminal to which input analog signals from a plurality of input terminals are respectively applied, an npn transistor to whose base the output of the input stage transistor is applied, and an emitter of the npn transistor. a composite transistor circuit corresponding to the input terminal, comprising a pnp transistor connected to the base; and a switching control including a transistor corresponding to the composite transistor circuit, which controls operation and non-operation of the composite transistor circuit according to a switching control signal. An analog switch circuit comprising: a current source common to the transistors of the switching control circuit; and a temperature compensation diode connected in series with the PNP transistor of the composite transistor circuit.