JPS61264913A - Analog switch circuit for single power supply - Google Patents

Abstract

PURPOSE:To connect directly the titled circuit to a circuit of the next stage in the same IC chip by making a current flowing to a load resistor of a differen tial amplifier when an output of the differential amplifier goes off a half of a current when the output goes on. CONSTITUTION:Transistors (Trs) 5, 6 of a differential pair are connected in parallel and the collector of the Tr 5 is connected to a connecting point between a resistor R2 and a collector of a Tr 2. The point is used as an output and a resistor R8 is made equal to a resistor R1 so as to flow the same current to the Trs 5, 6 when a Tr 3 is turned off. In turning on/off a continuous bipolar signal inputted to a Tr 1 of the differential amplifier by using a digital signal inputted to the Tr 3 of the differential pair, when the digital signal is at an L level and the Tr 3 is turned off, the current flowing to the resistor R2 is a half of a current I' flowing to the resistor R2 when the Tr 3 is turned on and the output voltage is clamped to the center of the amplitude of the bipolar signal. Thus, no capacitor is required, the circuit integration is facilitated, no output signal is required and the titled circuit is connected directly to a circuit of the next stage.

Description

[Detailed Description of the Invention] [Summary] In a single power supply analog switch circuit that switches continuous bipolar signals using a digital signal, when the output is off, the output is clamped to the center value of the amplitude of the bipolar signal. If the output of the differential amplifier is turned off, the load of the differential amplifier is By configuring the current flowing through the resistor to be half of that when the output is on, it is easy to integrate it into an IC and the number of output terminals can be reduced.

[Industrial application field]

In the present invention, as in the case of dividing the supervisory control signal of a repeater in a wired communication system, the next stage is composed of a differential amplifier, and when the output is off, the center value of the amplitude of the bipolar signal when the output is off is This invention relates to an improvement in a single power supply analog switch circuit for switching continuous bipolar signals using digital signals when the output is connected to a differential amplifier circuit whose output would otherwise be biased to one side and increase distortion.

As mentioned above, the single power supply analog switch circuit used when the next stage is a differential amplifier circuit is easy to integrate into an IC, has a small number of output terminals, and allows each circuit to be directly connected within the same IC chip. It is desirable to be able to do so.

[Conventional technology]

Figure 3 is a circuit diagram of a conventional single power supply analog switch circuit, Figure 4 is a time chart of waveforms at various parts in the case of Figure 3, and (A) to (D) are a-d in Figure 3. corresponds to the point.

In the figure, 1 is a constant current source, Tri to Tr4 are transistors, R
1-R7 is a resistor, and the values of R1 and R2 are equal, and R3 and R4
The values of are equal, C1 is the capacitor, ■ is the power supply voltage, Vr
efl and Vref2 indicate reference voltages.

To explain the operation, the continuous bipolar signal shown in FIG.
1 to R4.

On the other hand, the digital signal shown in FIG. 4(B) is transmitted through the transistor Tr3. It is input to a differential pair consisting of Tr 4 and resistor R7.

When the digital signal is at H level, the transistor Tr3 is turned on, and the current flows through the differential amplifier as indicated by the solid arrow.
flows, and an AC signal of amplitude I°·R2 shown in FIG. 4(C) corresponding to the bipolar input signal is obtained at point C. (1
' is the current flowing through the resistor R2) When the digital signal is at L level, the transistor Tr3
is turned off, and as shown in FIG. 4(C), the potential at point C becomes the ground potential, and the output is clamped to the ground potential.

Therefore, the voltage Vof when the bipolar signal output is off
f cants the DC component with a large capacity capacitor CI,
This can be obtained by selecting the values of the resistors R5 and R6 as shown in the following formula.

V o f f = V - R5 / (R5 + R6) Therefore, the waveform at the output point d is as shown in Figure 4 (D). When the output is off, the output has the amplitude of the bipolar signal. is clamped to the center value.

[Problem that the invention seeks to solve]

However, when converting the circuit into an IC, it is difficult to convert this large capacity capacitor C1 into an IC, and since it has to be installed outside the IC, there are problems with the large size and the need for two terminals for this capacitor. Therefore, there is a problem that it becomes impossible to connect directly to the next stage circuit within the same IC chip.

[Means for solving problems]

The above problem is solved by combining a differential amplifier that manually handles bipolar signals with a differential pair that controls the drive current of the differential amplifier with a digital signal to turn on and off the bipolar signal. This problem is solved by the single power supply analog switch circuit of the present invention, which is configured so that when the output is off, the current flowing through the load resistor of the differential amplifier is 1/2 that when the output is on.

[Effect]

According to the present invention, a differential amplifier to which a bipolar signal is input and a differential pair that controls the drive current of the differential amplifier by a digital signal are combined, and the difference is calculated when the output of the differential amplifier is turned off. The current flowing through the load resistance of the dynamic amplifier is configured so that it is half of that when the output is on, and the current flowing through the load resistance of the dynamic amplifier is clamped to the center value of the bipolar signal amplitude when the output is off. It is not necessary, the size is small, and if it is integrated into an IC, an output terminal is not necessary, and it can be directly connected to the next stage circuit in the same RC chip.

〔Example〕

FIG. 1 is a circuit diagram of a single power supply analog switch circuit according to an embodiment of the present invention, and FIG. 2 is a time chart of waveforms at various parts in the case of FIG. It corresponds to point a''-c.

2 in the figure is a constant current source, Tr5. Tr6 is a transistor, R
Reference numeral 8 indicates a resistor, and the same reference numerals indicate the same functions throughout the drawings.

The difference between FIG. 1 and FIG. 3 is that one transistor of the differential pair is connected to two parallel transistors (Tr5.
6), and the collector side of one transistor Tr5 is
It is connected to the connection point between the resistor R2 and the collector of the transistor Tr2, this point is used as an output, and the value of the resistor R8 is changed to the value of the transistor Tr5 when the transistor Tr3 is off. This point is made equal to the value of the resistor R1 so that the same value of current flows through the Tr6.

In this way, the continuous bipolar signal shown in FIG. 2(A) inputted to the transistor Tri of the differential amplifier is inputted to the transistor Tr3 of the differential pair as shown in FIG. 2(B).
When turning on and off with the digital signal shown in , when the digital signal becomes L level and transistor Tr3 turns off, current I/2 flowing through resistor R2 is
When r3 is on, the current I' flowing through resistor R2 becomes 1/2, and the output voltage is clamped to the center value of the amplitude of the bipolar signal, as shown in FIG. 2(C).

Therefore, there is no need for a capacitor, it is easy to integrate into an IC, and there is no need for an output terminal, and when integrated into an IC, it can be directly connected to the next stage circuit in the rc chip.

〔Effect of the invention〕

As explained in detail above, according to the present invention, when configuring a single power supply analog switch circuit used when the next stage is a differential amplifier circuit, a capacitor is not necessary, and an I
This has the advantage of being easy to convert into a C, eliminating the need for an output terminal, and allowing direct connection to the next stage circuit within the same IC chip.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a single power supply analog switch circuit according to an embodiment of the present invention, Fig. 2 is a time chart of waveforms of various parts in the case of Fig. 1, and Fig. 3 is a conventional example of a single power supply analog switch circuit. A circuit diagram of the switch circuit. FIG. 4 is a time chart of waveforms of various parts in the case of FIG. 3. In the figure, 1.2 is a constant current source, Tri to Tr6 are transistors, R1 to R8 are resistors, CI is a capacitor, (2) is a power supply voltage, and Vrefl and Vref2 are reference voltages. $1g

Claims (1)

[Claims] The differential amplifier comprises a differential amplifier into which a bipolar signal is input, and a differential pair that controls the drive current of the differential amplifier with a digital signal in order to turn on and off the bipolar signal. 1. An analog switch circuit for a single power supply, characterized in that when the output of the differential amplifier is turned off, the current flowing through the load resistor of the differential amplifier is 1/2 that when the output is on.