JPH0145252B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electronic switch circuits for analog signals.

An electronic switch circuit as shown in FIG. 1 was proposed prior to this invention.

This circuit consists of two pairs of differential transistors Q ₁ and Q ₂
and the corresponding transistor Q ₁ in Q ₃ , Q ₄ ,
A common load is provided by a current mirror circuit consisting of a diode-type transistor (or the same applies below) Q ₁₀ and a transistor Q ₁₁ , with the collectors of Q ₃ , Q ₂ , and Q ₄ connected in common, and one differential The bases of transistors Q ₁ and Q ₃ are input terminals IN ₁ and IN ₂ to which analog input signals are applied, respectively.
The bases of the other differential transistors Q ₂ and Q ₄ are connected in common to the output terminal OUT from which the output signal is obtained, and the respective differential transistors Q ₁ ,
Q ₂ , Q ₃ , and Q ₄ are configured as a voltage follower circuit. Note that the output signal is formed via an emitter follower circuit composed of a transistor _Q12 and a resistor _R12 .

And each of the above differential transistors Q ₁ ,
Constant current transistors Q ₇ and Q ₈ are provided at the common emitters of Q ₂ and Q ₃ and Q ₄ , and by selectively operating these transistors Q ₇ and Q ₈ ,
By operating only one differential transistor Q ₁ , Q ₂ or Q ₃ , Q ₄ , either input terminal IN ₁ or IN ₂
The analog signal applied to the output terminal is transmitted to the output terminal.

As a control circuit for selectively operating the constant current transistors Q ₇ and Q ₈ , the differential transistor
A constant current switching circuit using pnp transistors of conductivity type opposite to Q ₁ to _{Q 4} is used.

That is, a diode-type transistor Q that forms _a current mirror circuit together with the constant current transistors Q ₇ and Q ₈ is connected to the collectors of the differential transistors Q ₁₃ and Q ₁₄ whose emitters are commonly connected to the constant current circuit I 0 . ₁₅ and Q ₁₆ are provided respectively.
Then, the reference voltage V ₁ is applied to the base of one transistor Q ₁₃ , and the control signal V _C is applied to the base of the other transistor Q ₁₄ .

The operation of this circuit is as follows: control signal V _C > reference voltage V ₁
When , transistor _Q13 turns on and a constant current _I0 flows through transistor _Q15 , so a similar constant current flows through the collector of constant current transistor _Q7 , transmitting the input signal from input terminal _IN1 to output terminal OUT. death,
If control signal V _C < reference voltage V ₁ , transistor
Q ₁₄ is turned on and switched to transmit the input signal at input terminal IN ₂ to output terminal OUT.

In this circuit, a differential transistor is generally used.
Since there is a difference in the offset voltage of the differential input due to variations in the base-emitter voltage V _BE between Q ₁ , Q ₂ and Q ₃ , Q ₄ , the constant current transistors Q ₇ ,
If _Q8 is switched digitally, the output DC level will fluctuate and a pop sound will occur when switching.
As mentioned above, unlike the case where the output signal is fed back 100%, if the feedback factor β is set to 1 or less and a predetermined gain (1/β) is set, a large pop-up proportional to the offset voltage of the difference multiplied by this gain will be generated. A sound is produced.

Therefore, in the above circuit, by slowing down the voltage change of the control signal V _C and gradually (softly) switching the constant current, there is an advantage that the occurrence of the pop sound can be prevented or significantly reduced. .

However, in this circuit, the switching position is
Since it can only take two states, IN ₁ and IN ₂ , its uses are limited.

An object of the present invention is to provide an electronic switch circuit that can easily switch between three or more states.

According to the basic feature of the present invention, as a control signal for selectively operating constant current transistors respectively provided at the common emitters of at least three pairs of differential transistor circuits each having a common collector output, The above-mentioned differential transistor is composed of a transistor of the opposite conductivity type, and the constant current supplied from the common emitter is switched between one output by the first differential transistor and the other output by the second differential transistor. Two outputs switched by are used.

Hereinafter, this invention will be explained in detail together with examples.

FIG. 2 shows a circuit diagram showing one embodiment of the present invention.

In this embodiment, a differential transistor similar to that described above is used.
In addition to Q ₁ to _{Q 4} , a pair of differential transistors Q ₅ ,
Q ₆ is added, one differential transistor
The base of Q ₅ is connected to the third input terminal IN ₃ , and the base of the other differential transistor Q ₆ is connected to the output terminal OUT in the same way as transistors Q ₂ and Q ₄ . A third constant current transistor _Q9 is provided at the common emitter of the differential transistors _Q5 and _Q6 , forming a three-state electronic switch circuit.

Note that the collectors of the transistors Q ₁ , Q ₃ , Q ₅ and the transistors Q ₂ , Q ₄ , and Q ₆ are connected in common as described above, and form a current mirror composed of a diode-type transistor Q ₁₀ and a transistor Q ₁₁ . A circuit is provided as a load and an output signal is obtained via the emitter follower output circuit Q ₁₂ , R ₁ .

In this embodiment, as a control circuit for selectively operating the constant current transistors, two pairs of differential transistors each consisting of a pnp transistor of a conductivity type opposite to the differential transistors Q ₁ to _{Q 6} are used.
Q ₁₃ , Q ₁₄ and Q ₁₇ , Q ₁₈ are used.

That is, a constant current circuit I ₀ is provided at the commonly connected emitters of the differential transistors Q ₁₃ and Q ₁₄ , and a first reference voltage V ₁ is applied to the base of the transistor Q ₁₃ .

A diode-type transistor _Q15 is provided at the collector of the transistor _Q13 , and forms a current mirror circuit together with a constant current transistor _Q7 . The collector of transistor Q ₁₄ is connected to the common emitter of differential transistors Q ₁₇ and Q ₁₈ . A second reference voltage V ₂ lower than the first reference voltage V 1 is applied to the base of the transistor _{Q 17} , and a control signal V _C is commonly applied to the bases of the transistors Q ₁₄ and Q ₁₈ . Transistor Q ₁₇ ,
Diode-type transistors Q ₁₆ and Q ₁₉ are provided at the collector of Q ₁₈ , respectively, and constitute a current mirror circuit together with constant current transistors Q ₈ and Q _9, respectively.

In the operation of this embodiment circuit, when V _C >V ₁ , differential transistors Q ₁₃ and Q ₁₇ are turned on.
Therefore, when the transistor Q ₁₃ is turned on, the constant current I ₀ flows through the differential transistors Q 1 and Q ₁ through the current mirror circuit composed of the transistors Q ₁₅ and Q ₇ .
Flows to Q ₂ . This allows the differential transistors Q ₁ ,
Only Q ₂ operates and transmits the input signal on input terminal IN ₁ to output terminal OUT.

At this time, even if the transistor _Q17 is on, the constant current _I0 does not flow through the transistor _Q17 because the transistor _Q14 is off.

Next, when V ₁ > V _C > V ₂ , differential transistors Q ₁₄ and Q ₁₇ are turned on. Therefore, the constant current I ₀ passing through these transistors Q ₁₄ and Q ₁₇ flows to the differential transistors Q ₃ and Q ₄ via a current mirror circuit made up of transistors Q ₁₆ and Q ₈ . As a result, only the differential transistors Q ₃ and Q ₄ operate, and the input signal from the input terminal IN ₂ is transferred to the output terminal OUT.
to communicate.

Next, when V ₁ > V _C , the differential transistor
Q ₁₄ and Q ₁₈ turn on. Therefore, the constant current I ₀ passing through these transistors Q ₁₄ and Q ₁₈ flows to the differential transistors Q ₅ and Q ₆ via a current mirror circuit made up of transistors Q ₁₉ and Q ₉ . As a result, only differential transistors Q ₅ and Q ₆ operate,
Transmits the input signal from input terminal IN ₃ to output terminal OUT.

In this way, a three-state switching operation can be performed.

In the above switching operation, if the change in control signal V _C is slowed down, the differential transistor
Since the current switching operations of Q ₁₃ , Q ₁₄ , Q ₁₇ , and Q ₁₈ can be carried out linearly, it is possible to prevent or significantly reduce pop noises, as described above. The control signal V _C can be easily changed as described above by using an integrating circuit or the like.

FIG. 3 shows another preferred embodiment of the circuit of the present invention.

In this embodiment, the circuit elements of the parts surrounded by dotted lines are formed on a single-chip silicon substrate by a well-known semiconductor manufacturing method, and the numbers surrounded by circles indicate terminal numbers.

This embodiment circuit is used as a microphone input switching circuit in a magnetic tape recording/reproducing device or the like.

That is, in order to cause the differential transistors Q ₁ and Q ₂ to perform a mute operation, only the bias voltage V _B1 is applied to the base of the transistor Q ₁ via the resistor R ₃ , and the base of the transistor Q ₂ In this case, 100% of the output signal is fed back and configured as a voltage follower circuit.

The differential transistors Q ₃ and Q ₄ are provided for a low impedance (for example, 600Ω) microphone, and the base of the transistor Q ₃ is
Similarly to the above, the bias voltage V _B1 is applied via the resistor R ₂ and is connected to the No. 1 terminal.
On the other hand, the base of transistor Q ₄ has a resistor R ₁₄ ,
An output signal divided by _R15 is applied, and the gain is set to, for example, 35 dB.

In addition, the differential transistors Q ₅ and Q ₆ are so-called DIN transistors with high impedance (for example, 470KΩ).
Provided for standard microphones.

Similarly to the above, the base of the transistor Q ₅ is applied with the bias voltage V _B1 via the resistor R ₁ and is commonly connected to the No. 1 terminal. On the other hand, an output signal divided by resistors R ₁₆ and R ₁₇ is applied to the base of transistor Q ₆ , and for example, the gain is
Set to 25dB.

In addition, in this embodiment, a diode _Q23 is used to prevent reverse current due to a signal level exceeding the base and emitter breakdown voltage of the differential transistor that is off.
~ _Q28 are inserted in the forward direction at the emitters of the differential transistors _Q1 ~ _Q6 .

Further, the emitter of the output transistor Q ₁₂ similar to the above is connected to diodes Q ₂₉ and Q ₃₀ and a constant current circuit I′ ₀
are provided in series to form a drive circuit for the push-pull output transistors Q ₃₁ and Q ₃₂ .

Furthermore, in the second embodiment, a differential transistor
Since differential transistors Q ₁₇ and Q ₁₈ and diodes Q ₁₆ and Q ₁₉ forming a current mirror circuit are provided in Q ₁₄ , voltage reduction characteristics deteriorate.

Therefore, in the embodiment circuit of FIG. 3, the collector output current of the differential transistor _Q14 is
It is converted into a sink current by a current mirror circuit composed of Q′ ₁₆ and a transistor Q ₂₀ , and further converted into a push current through a diode Q ₂₁ and a transistor Q ₂₂ provided on the power supply voltage V _CC side. , are supplied to the emitters of differential transistors Q ₁₇ and Q ₁₈ similar to the above.

Thereby, it is possible to improve the voltage reduction characteristics. In particular, when configuring a large number of switching positions N, N-1 differential transistors for switching control are required, and if these are connected in series as in the embodiment circuit shown in FIG. This deteriorates the voltage reduction characteristics, but in this embodiment, the lower limit operating voltage can be set regardless of the number of switching positions.

In this embodiment, the diodes or transistors constituting each current mirror circuit are provided with resistors R ₄ to R ₁₁ for stabilizing operation.

As in this example, when the gain differs depending on the switching position, a DC voltage corresponding to the offset voltage multiplied by the respective gain is output, so if the switching is done digitally, a loud pop sound will be produced. However, by slowing down the change in the control signal V _C as described above,
These popping sounds can be prevented from occurring.

The present invention is not limited to the embodiments described above, and a switching circuit with four or more states can be created using the same technical idea as described above. Alternatively, the conductivity types of the transistors may all be reversed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an electronic switch circuit proposed prior to the present invention, and FIGS. 2 and 3 are circuit diagrams each showing an embodiment of the present invention.

Claims (1)

[Claims] 1. Corresponding collectors are commonly connected,
three pairs of differential transistors configured by transistors of a first conductivity type, each having an input signal applied to one base and having the other base connected in common; one of the common collector connections and the common base; a controlled circuit having at least a common negative feedback circuit connected between the first to third constant current transistors connected to the common emitter connection of the differential transistor pair; An electronic switch circuit comprising: a control circuit for selectively selecting one of first to third constant current transistors, the control circuit having a constant current source connected to a common emitter connection; a first reference voltage is applied to the other base, a control signal is applied to the other base, and the first difference is configured by a transistor of a second conductivity type having a conductivity type opposite to the first conductivity type. a first differential transistor, which receives the collector current of one of the first differential transistor and the first differential transistor, and is configured of a first conductivity type transistor.
and a second current mirror circuit configured with a transistor of a second conductivity type, which receives the output current of the first current mirror circuit as an input, and shares the output current of the second current mirror circuit. a second differential transistor configured of a transistor of a second conductivity type, the second reference voltage being applied to one base and the control signal being applied to the other base; An electronic switch characterized in that the other collector of the first differential transistor and the one and the other collectors of the second differential transistor are connected to the bases of the first to third constant current transistors, respectively. circuit. 2 Corresponding collectors are commonly connected,
An input signal is applied to one base, and three pairs of differential transistors are configured by transistors of a first conductivity type; one of the common collector connections and the other base of each of the differential transistor pairs; a controlled circuit having at least first to third negative feedback circuits respectively connected between the two, and first to third constant current transistors respectively connected to the common emitter connection of the differential transistor pair; ,
an electronic switch circuit comprising a control circuit for selectively selecting the first to third constant current transistors, the control circuit having a constant current source connected to a common emitter connection; A first reference voltage is applied to the base of the transistor, a control signal is applied to the other base of the transistor, and the first transistor is configured of a transistor of a second conductivity type having a conductivity type opposite to the first conductivity type. and a first current mirror circuit constituted by a transistor of a first conductivity type, which inputs the collector current of one of the first differential transistors, and the first current mirror circuit of the first current mirror circuit. A second current mirror circuit which receives the output current as an input and is composed of transistors of a second conductivity type, receives the output current of the second current mirror circuit through a common emitter connection, and has one base connected to a second reference voltage. is applied to the other base, the control signal is applied to the other base, and the second differential transistor is constituted by a transistor of a second conductivity type, the other collector of the first differential transistor, the second An electronic switch circuit characterized in that the collectors of one and the other of the differential transistors are connected to the bases of the first to third constant current transistors, respectively. 3. The electronic switch circuit according to claim 2, wherein the first to third negative feedback circuits have different feedback rates.