JP3100804B2 - Analog switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog switch for interrupting and conducting a signal with a bipolar transistor in an electronic circuit.

[0002]

2. Description of the Related Art Conventionally, switches and relays have been used in electronic circuits to switch connections between circuits. On the other hand, in recent years, analog switches have become widespread for miniaturization, digitization, or high reliability of devices. In a conventional analog switch, as shown in FIG. 7, an FET (field effect transistor) 51 is mainly used as a switching element. Hereinafter, this analog switch will be described.

This analog switch is provided with a comparator 5
2 having a control terminal 53 at its non-inverting input terminal.
, While the reference voltage is input to the inverting input terminal. The reference voltage is obtained by dividing the power supply voltage V _CC by the resistors 54 and 55 connected in series. The comparator 52 compares the control voltage with the reference voltage, and sets the output to “H” when the control voltage is higher than the reference voltage, and sets the output to “L” when the control voltage is opposite. I have.

Further, the output terminal of the comparator 52
The cathode of the diode 56 and one terminal of the capacitor 57 are connected. The anode of the diode 56 and the other terminal of the capacitor 57 are connected to the gate of the FET 51.

The FET 51 is of Nch type, and has a source connected to the signal terminal 58 and a drain connected to the output terminal 59.
It is connected to the. In the FET 51, the gate and the source are connected to each other via the resistor 60.

In the above-described analog switch, the control voltage input from the control terminal 53 and the reference voltage are compared by the comparator 52. When the control voltage is higher than the reference voltage, the output of the comparator 52 becomes "H". . At this time, when the diode 56 is turned off, the FET 51 is turned off.
Is turned on, and the signal terminal 58 and the output terminal 59 are connected.

On the contrary, when the control voltage is smaller than the reference voltage, the output of the comparator 52 becomes "L". At this time, when the diode 56 is turned on, the FET 51 is turned off, and the connection between the signal terminal 58 and the output terminal 59 is cut off.

[0008]

By the way, electronic circuits are being integrated into ICs with the advance of today's integrated circuit technology, and analog switches are no exception. However, when the above analog switch is integrated into an IC,
Incorporating the FET 51 requires a complicated IC manufacturing process, which leads to an increase in manufacturing cost. Moreover,
Since a peripheral circuit is required, there is a problem that the chip cost is increased.

The present invention has been made in view of the above circumstances, and has as its object to configure an inexpensive analog switch with a simple structure using bipolar transistors.

[0010]

According to a first aspect of the present invention, there is provided an analog switch, comprising: a signal circuit for transmitting a signal voltage;
In order to solve the above-mentioned problem, an analog switch including a control circuit that controls connection and disconnection of an input and output of a signal circuit by applying a control voltage is characterized by taking the following means. .

The control circuit is composed of a first transistor, while the signal circuit is composed of an emitter follower circuit having a second transistor, and is an analog switch in which the emitters of the first and second transistors are connected together. And a current having the same value as the current flowing through the collector of the second transistor flows between the collector of the first transistor and the collector of the second transistor so as to flow through the collector of the first transistor. A current mirror circuit, wherein a base and a collector of the first transistor are connected, and a first transistor
ON / OFF operation of the first transistor at the base of the
The control terminal for inputting the control voltage to be controlled is set.
Have .

[0012]

The current flowing through the load (constant current circuit) connected to the emitter of the second transistor in the emitter follower circuit is represented by I, and the first transistor and the second transistor
The currents flowing through the respective transistors are I ₁ and I ₂ .

The first transistor is turned on by the control voltage
When I ≒ I ₁ , no current flows through the second transistor of the emitter follower circuit. As a result, the input and output of the signal circuit are cut off, and no signal voltage is output. When the first transistor is turned off, a current flows through the second transistor, and I ≒ I ₂ . Thereby, the input and output of the signal circuit are connected, and a signal voltage is output.

In the analog switch according to the first aspect, when the first transistor is turned on and I ≒ I ₁ ,
No current flows through the second transistor, the input and output of the signal circuit are cut off, and no signal voltage is output. On the other hand, when the first transistor is turned off and I ≒ I ₂ , the input and output of the signal circuit are connected, and a signal voltage is output.

As described above, in the analog switch according to the first aspect, disconnection between input and output of the signal circuit is controlled by whether or not the control voltage is applied to the first transistor.

Further, the current mirror circuit attempts to cause a current having the same value as the current flowing through the second transistor to flow through the first transistor. Since the base and the collector of the first transistor are connected, a part of the current flowing from the current mirror circuit is supplied to the base of the first transistor. For this reason, the signal voltage and the control voltage become equal and stable.

Accordingly, when the control voltage is not applied to the first transistor, the same voltage as the signal voltage applied to the base of the second transistor appears at the base of the first transistor. Therefore, when the first transistor is used as a control terminal for applying a control voltage, the control terminal can be used as an output terminal from which a signal voltage is output.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing an analog switch according to the present invention, an analog switch having a basic configuration of an embodiment described later will be described below with reference to FIGS.

As shown in FIG. 1, the analog switch as a basic configuration includes NPN-type transistors 1 and 2 and a constant current circuit 3.

The transistors 1 and 2 both have collectors connected to a power supply terminal 4, and a power supply voltage V _CC is applied through the power supply terminal 4. Transistor 1
2 has an emitter connected to one end of the constant current circuit 3 and an output terminal 7. The constant current circuit 3 has the other end connected to the GND terminal 5.

The transistor 1 which constitutes the signal circuit and is also the second transistor has a signal terminal 6 at its base.
Is connected. The transistor 1 forms an emitter follower circuit together with the constant current circuit 3 serving as a load. On the other hand, the control terminal 8 is connected to the base of the transistor 2 which constitutes the control circuit and is also the first transistor. Also, the signal terminal 6 and the GND terminal 5
Are connected to both ends of the signal source 9.

The operation of the analog switch configured as described above will be described.

The transistors 1 and 2 of the base voltages applied, that is, the signal voltage and the control voltage and the a V _b - V _a, respectively, the currents flowing through the emitter of the transistor 1, 2 and I ₁ · I _2, Assuming that the current flowing through the constant current circuit 3 is I, the currents I ₁ and I ₂ are given by the following equation (1).
It is represented by equation (2).

I ₁ = I / [1 + exp ((V _b −V _a ) / VT)] (1) I ₂ = I / [1 + exp ((V _a −V _b ) / VT)] = I−I ₁ (2) In the above equation, VT = k · T / q, where k is Boltzmann's constant, T is absolute temperature, and q is the amount of charge. Then, when the above equation is drawn on a graph, it becomes as shown in FIG.

In the above analog switch, a signal voltage is applied to the base of the transistor 1 through the signal terminal 6. Also, the base of the transistor 2
A control voltage is applied through a control terminal 8.

In this state, when the transistor 2 is turned on by the control voltage and I ≒ I ₂ , as shown in FIG. 2, no current flows through the transistor 1 and the signal circuit is cut off. Therefore, in this case, no signal voltage is output. On the other hand, a current flows through the transistor 1 I ≒ I ₁ becomes the signal circuit becomes conductive transistor 2 is turn OFF. Therefore, in this case, a signal voltage is output. That is, when V _a ≫V _b , the transistor 1
And N, to OFF when V _a «V _b.

As described above, in the analog switch, a switch function can be realized with a simple configuration including the transistors 1 and 2 and the constant current circuit.

[0028] If described with reference to FIGS. 2 to 4 for the embodiment of EXAMPLES present invention is as follows. The components of the present embodiment having the same functions as those of the analog switch as the basic configuration are denoted by the same reference numerals, and the description thereof will be omitted.

The analog switch according to this embodiment is similar to the one shown in FIG.
As shown in the figure, similar to the analog switch as the basic configuration, the semiconductor device includes NPN transistors 1 and 2 and a constant current circuit 3, and further includes a PNP transistor 1.
1 and 12 are provided.

The transistors 11 and 12 have their emitters connected to the power supply voltage V _CC , and their bases connected to the collector of the transistor 1. In the transistor 11, the collector and the base are connected to each other, and the collector is connected to the collector of the transistor 1. The transistor 12 has a collector connected to the collector of the transistor 2. The current mirror circuit 13 is configured by the above connection of the transistors 11 and 12. The transistor 2 has a collector and a base connected to each other.

In the analog switch configured as described above, when attention is paid only to the transistors 1 and 2 , when the transistor 2 is turned on by the control voltage and I ≒ I ₂ , as shown in FIG. When no current flows, the signal circuit is cut off. Therefore, in this case, no signal voltage is output. On the other hand, transistor 2
Is turned off and a current flows through transistor 1, I ≒ I ₁
And the signal circuit becomes conductive. Therefore, in this case, a signal voltage is output.

In the present analog switch, the current mirror circuit 13 tries to supply a current of the same value to the transistors 1 and 2. When the control terminal 8 is open, a part of the current flowing through the collector of the transistor 12 of the current mirror circuit 13 is supplied to the base of the transistor 2, so that the transistor 2 is turned on and the current I / 2 substantially equal to that of the transistor 1 is generated. Flows. Thus, as shown in FIG. 2, stabilized in a state in which a V _a = V _b, the signal voltage appearing at <br/> control terminal 8 in an open state.

As described above, according to the present analog switch, the switch function can be realized with a simple configuration using the transistors 1 and 2 and the constant current circuit, similarly to the analog switch as the basic configuration.

Thus, for example, when the analog switch is built in an IC 14 as shown in FIG.
By using the control terminal 8 as a test terminal, it is possible to measure a signal inside the IC 14 or to input a signal from the outside. In addition, by grounding the control terminal 8, it is possible to prevent an internal signal from being output from the control terminal 8. Moreover, according to this analog switch, since the current mirror circuit 13 is provided and the collector and base of the transistor 2 are connected, the control terminal 8
The control terminal 8 can be used as an output terminal.

Specifically, in the IC 14, a signal processing circuit 15 is provided between the signal terminal 6 and the base of the transistor 1, and a signal processing circuit 16 is provided between the emitters of the transistors 1 and 2 and the output terminal 7. Is provided.

In such an IC 14, after the signal input from the signal terminal 6 is processed by the signal processing circuit 15, the signal passes through the emitter follower circuit and passes through the signal processing circuit 16.
And output to the control terminal 8 as well. In this case, since a signal that does not pass through the signal processing circuit 16 is output from the control terminal 8, it is possible to test only the signal processing circuit 15.

When the control terminal 8 is grounded, the IC 1
4, the output of the signal processing circuit 15 does not appear.
That is, in this case, it is possible to prevent the external influence of the IC 14 from being given to the signal processing circuit 16 via the control terminal 8.

Further, when a signal is input to the control terminal 8 in a state where a voltage higher than the bias voltage applied to the base of the transistor 1 is applied to the control terminal 8, this signal is output from the signal processing circuit 15. Is input to the signal processing circuit 16 in place of. Therefore, in this case, it is possible to test only the signal processing circuit 16.

By the way, if the analog switch as the basic configuration is made into an IC like the IC 14,
The control terminal 8 can be used as a test terminal.
However, since the analog switch cannot output a signal from the control terminal 8, a signal is input from the control terminal 8 or the control terminal 8 is grounded when no signal is input.

Although the analog switch of the present embodiment and the analog switch as the basic configuration have the NPN transistors 1 and 2, they have PNP transistors having polarities different from those of the transistors. There may be.

The above-described analog switch has one signal source.
The analog switch of the basic configuration
Switch to cut off the signal voltage of the two signal sources.
It is also possible to configure an analog switch that switches and outputs
Noh.

The analog switch in this case includes analog switches 21, 22, and 23 and an inverting circuit 24, as shown in FIG.

The analog switches 21 and 22 have the same configuration as the analog switch as the basic configuration. The analog switch 21 is connected to the first analog switch.
Switch, the analog switch 22 is connected to the second analog switch.
Switch.

The analog switch 23 is connected to the transistor 2
5 and 26 and a constant current circuit 27 are provided. The PNP transistors 25 and 26 have their emitters both connected to one end of the constant current circuit 27 and the output terminal 7. The other end of the constant current circuit 27 is connected to the power supply terminal 4. The transistors 25 and 26 have their collectors connected to the GND terminal 5.

The base of the transistor 25 is connected to the output terminal 2
8 is connected to the emitters of the transistors 1 and 2 in the analog switch 21. On the other hand, the base of the transistor 26 is connected to the emitters of the transistors 1 and 2 in the analog switch 22 via the output terminal 29.

The analog switch 23 comprises transistors 25 and 26 having polarities opposite to those of the transistors 1 and 2 and is a third analog switch.

The inverting circuit 24 includes transistors 30 and 31
, Resistors 32 and 33, and a constant current circuit 34.

The NPN transistors 30 and 31 have collectors connected to the power supply terminal 4 via resistors 32 and 33, respectively, and emitters both connected to one end of the constant current circuit 34. The other end of the constant current circuit 34 is connected to the GND terminal 5. The collector of the transistor 30 is connected to the base of the transistor 2 of the analog switch 22 via the control terminal 35. On the other hand, the collector of the transistor 31 is connected to the base of the transistor 2 of the analog switch 21 via the control terminal 36. Further, the base of the transistor 30 is connected to the control terminal 8, and the base of the transistor 31 is connected to the reference power supply 3.
7 are connected to the positive terminal. This reference power source 37
The negative terminal is connected to the GND terminal 5.

The inverting circuit 24 changes the voltage applied to the control terminal 8 to control the control terminals 35 and 36.
The voltage that appears to have become so as to be inverted with respect to each other, this
This is referred to as inversion means.

The operation of the analog switch configured as described above will be described.

Here, the voltage applied to the control terminal 8 is V
_c , the voltage of the reference power supply 37 is _Vd , and the resistance 32.3
3 are R, the voltage values appearing at the control terminals 35 and 36 are _Ve · _Vf , and the current flowing through the constant current circuit 34 is I ′, the voltage _Ve · _Vf is (3 )
Expression (4)

V _e ≒ V _CC −I ′ · R / [1 + exp ((V _d −V _c ) / VT)] (3) V _f ≒ V _CC −I ′ · R / [1 + exp ((V _c − _Vd ) / VT)] (4) When these equations are drawn in a graph, they are as shown in FIG.

In the above analog switch, a signal voltage is applied to the bases of the transistors 1.1 of the analog switches 21 and 22 by the signal sources 38 and 39 through the control terminals 40 and 41. A control voltage is applied to the base of the transistor 30 of the inverting circuit 24 through the control terminal 8.

When the control voltage is changed in this state, the voltages V _e and V _f appearing at the control terminals 35 and 36 are inverted with each other. Since the voltages V _e and V _f are inverted from each other as described above, the analog switch 21
22 outputs the signal voltage of only one of them. At this time, the output terminal 7 of the analog switch 21 or the analog switch 22 that does not output a signal voltage becomes “H”.

For example, when the control voltage is changed to be high,
Increasing the current flowing through the transistor 30 is a voltage drop in the resistor 32 increases, the voltage V _e decreases. At this time, since the total current flowing through the transistors 30 and 31 is kept at a constant I 'by the constant current circuit 34, the current flowing through the transistor 31 decreases. As a result, the voltage drop at the resistor 33 decreases, and the voltage _Vf increases.

With such an operation, in the analog switch 21, the transistor 1 is turned on and no signal voltage is output. On the other hand, in the analog switch 22, the transistor 1 is turned off and a signal voltage is output. At this time, the output terminal 28 becomes “H”, while the signal voltage of the signal source 39 appears at the output terminal 29. Therefore, in the analog switch 23, the transistor 25 is turned off, while the signal voltage is applied to the base of the transistor 26, and the signal voltage is output to the output terminal 8.

[0057] When changing a low control voltage, the voltage V _f decreases in the reverse voltage V _e increases, the signal voltage of the signal source 38 from the analog switch 21 is outputted. At this time, in the analog switch 23, the transistor 26 is turned on by the output of the analog switch 22.
The signal voltage is output through the transistor 25 to perform FF.

In the above configuration, the analog switch 2
3 is functionally equivalent to the analog switches 21 and 22, but since the connection structure of the transistors 25 and 26 is symmetric, the bases of the transistors 25 and 26 have a function as a control terminal and a function as a signal terminal. It is possible to have. Thus, the bases of the transistors 25 and 26 are controlled by the control voltage so that the function as the control terminal and the function as the signal terminal are switched with each other.

As described above , in the above analog switch, the signal voltage of the signal sources 38 and 39 can be output by switching the analog switches 21 and 22 by the control voltage applied to the control terminal 8 by the inverting circuit 24. That is, according to the analog switch, it is possible to select and output one of two signals.

That is, in the above analog switch,
A first transistor and a second transistor
And the control voltage applied to each control circuit is inverted.
You. Thereby, the first or second analog switch
Only one of them is turned ON. And at this time, ON
The output from the switched analog switch is the third analog switch.
Signal voltage of the analog switch
The output becomes the control voltage of the third analog switch. I
Therefore, the voltage applied to the first or second analog switch is
Selected one of the signal voltages to be output.

As described above, in the above analog switch,
The emitters of the first and second transistors are both connected.
Is connected, for example, by the control voltage.
Is turned on, the emitter follower circuit
Load connected to the emitter of the second transistor
(Constant current circuit) causes current to flow through the first transistor
You. Therefore, current does not flow through the second transistor.
Signal between the input and output of the signal circuit, and the signal voltage is output.
Not. Also, if the first transistor is turned off, the signal
Signal to the emitter follower circuit (signal circuit)
Therefore, a current flows through the second transistor, and the
Connected to output a signal voltage.

The inverting means is a third analog switch.
Signals from the first and second analog switches through
Voltage, the two signal voltages are controlled by the control voltage.
It is possible to switch and output. Therefore,
If the above configuration is adopted, two signal voltages are switched
Providing an analog switch to output at a low cost with a simple structure
Can be

[0063]

As described above, the analog switch according to the first aspect of the present invention comprises: a signal circuit for transmitting a signal voltage;
An analog switch including a control circuit that controls connection and disconnection between input and output of the signal circuit by applying a control voltage, wherein the control circuit includes a first transistor, and the signal circuit includes a second transistor. An analog switch having an emitter follower circuit having the emitters of the first and second transistors connected together, wherein the analog switch is connected between the collector of the first transistor and the collector of the second transistor. A current mirror circuit arranged so that a current having the same value as the current flowing through the collector of the second transistor flows through the collector of the first transistor; the base and the collector of the first transistor are connected ; One of the transistors
Controls ON / OFF operation of the first transistor on the base
The control terminal for inputting the control voltage
You.

Since the emitters of the first and second transistors are connected together, for example, when the first transistor is turned on by a control voltage, the emitter is connected to the emitter of the second transistor in the emitter follower circuit. A current flows through the first transistor due to a load (constant current circuit). Therefore, no current flows through the second transistor, the input and output of the signal circuit are cut off, and no signal voltage is output. In addition, the first transistor is OF
When F is applied, in the emitter follower circuit (signal circuit) to which a signal is applied, a current flows through the second transistor, the input and output are connected, and a signal voltage is output.

In addition, the current mirror circuit attempts to supply a current having the same value as the current flowing through the second transistor to the first transistor, and a part of the current flowing from the current mirror circuit is supplied to the first transistor. Supplied to the base. For this reason, the signal voltage and the control voltage become equal and stable. Therefore, a signal voltage can be output through the first transistor. Therefore, if the configuration of claim 1 is adopted, another output portion of the signal voltage can be provided, and the function of the analog switch can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a basic configuration of an analog switch according to the present invention.

FIG. 2 is a diagram showing the basic configuration and actual operation of an analog switch of the present invention.
6 is a graph showing the operation characteristics of the analog switch according to the example .

FIG. 3 is a circuit diagram illustrating a configuration of an analog switch according to an embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration in which the analog switch of FIG. 3 is formed into an IC.

FIG. 5 is a circuit diagram showing a configuration of another analog switch according to the embodiment of the present invention.

FIG. 6 is a graph showing operating characteristics of another analog switch according to the embodiment of the present invention.

FIG. 7 is a circuit diagram showing a configuration of a conventional analog switch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transistor (signal circuit, 2nd transistor) 2 Transistor (control circuit, 1st transistor) 3 Constant current circuit 13 Current mirror circuit

Claims (1)

(57) [Claims] 1. An analog switch comprising: a signal circuit for transmitting a signal voltage; and a control circuit for controlling disconnection between input and output of the signal circuit when a control voltage is applied, wherein the control circuit comprises a first circuit. An analog switch in which the signal circuit comprises an emitter follower circuit having a second transistor, and the emitters of the first and second transistors are connected together; And a current mirror circuit arranged between the collector of the second transistor and a current of the same value as the current flowing in the collector of the second transistor so as to flow in the collector of the first transistor. The base and the collector of the first transistor are connected, and the base of the first transistor is
Control for controlling ON / OFF operation of the first transistor
An analog switch, wherein a control terminal for inputting a voltage is set .