JPH0690122A - Differential amplifier circuit - Google Patents

Abstract

PURPOSE:To provide the differential amplifier circuit which can be stably operated even under a much lower power supply voltage or can be stably operated both of under a low power supply voltage and under a high power supply voltage and can be easily manufactured. CONSTITUTION:Differential transistors Q1 and Q2 receive constant currents I1 and I2 through an output step transistor in the single step of an upstream constant current circuit at the collectors. Thus, voltage drop is reduced rather than the conventional case. The amplified fluctuating currents of input signals A and B flow out to branch lines connected to the collectors and turn to an output signal C by a current mirror (Q11, Q12) and current mirrors (Q21, Q22) and (Q23, Q24).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential amplifier circuit, and more particularly to a differential amplifier circuit operable even under a low power supply voltage.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional differential amplifier circuit compatible with a low power supply voltage. Here, Q1 and Q2 are a pair of differential transistors, Q4 and Q6, Q3 and Q5, Q7 and Q, respectively.
Reference numeral 8 constitutes a current mirror. In the pair of differential transistors (Q1, Q2), the base of the transistor Q1 receives one signal A of the pair of input signals and controls the emitter current according to the input signal A. Transistor Q2
The base receives the other signal B of the pair of input signals and controls the emitter current according to the input signal B. The sum of these emitter currents is kept constant by the constant current circuit downstream.

Therefore, when the emitter current through the transistor Q1 changes according to the input signal A, the emitter current through the transistor Q2 also changes in the opposite direction. Also,
When the emitter current through the transistor Q2 changes according to the input signal B, the emitter current through the transistor Q1 also changes in the opposite direction. From this relationship, the emitter current through the transistors Q1 and Q2 fluctuates in the opposite direction according to the difference between the input signals A and B.

Furthermore, the collector current through transistor Q1 is approximately equal to the emitter current, and transistor Q1
It is duplicated and detected as an inversion current by a current mirror composed of transistors Q3 and Q5 connected to the collector side of 1, and is again inverted by a current mirror composed of transistors Q7 and Q8. On the other hand, the collector current through the transistor Q2 is also almost equal to the emitter current, and is duplicated and detected as an inversion current by the current mirror composed of the transistors Q4 and Q6 connected to the collector side of the transistor Q2.

Then, a current signal consisting of the difference between these duplicated currents is output as an output signal C to the output line branched from the connection point between the transistor Q6 and the transistor Q8. The difference current of this duplicate current is the transistor Q1, Q
The fluctuation of the current through 2 is doubled. Therefore, the output signal C is obtained by amplifying the difference between the input signals.

[0006]

In such a conventional differential amplifier circuit, between the pair of power supply lines Vcc and GND,
The current mirror circuit, the differential transistor, and the constant current circuit are sequentially connected. Moreover, since the current mirror circuit is used as a detection circuit of the collector current of the differential transistor, the input stage transistor of the current mirror circuit is inserted and connected. However, since the input stage transistor of the current mirror circuit is used with its base and collector connected to each other, a voltage of VBE (1VF) is always generated between its emitter and collector. Therefore, the voltage applied to the differential transistor by this voltage becomes lower than the power supply voltage. Conversely speaking, the minimum operating voltage of the power supply voltage becomes higher accordingly. This is a problem because it is not possible to cope with the reduction in power supply voltage due to the recent miniaturization of devices and the extension of battery life.

On the other hand, by inserting and connecting a transistor circuit or a Schottky diode between the base and collector of the input stage transistor of the current mirror circuit (see FIG. 6), the base potential of the input stage transistor is changed to the differential transistor. Although a circuit has been proposed in which the minimum operating voltage is lowered by not restricting the operating voltage of the above, it is difficult to stabilize the operating state when a transistor circuit is used, and when a Schottky diode is used. However, since the material for the Schottky diode is limited, there remains a disadvantage that the semiconductor manufacturing process is restricted.
An object of the present invention is to solve the above-mentioned problems of the prior art and to stably operate even under a lower power supply voltage or stably under a lower power supply voltage or a higher power supply voltage. It is to realize a differential amplifier circuit that can operate and is easy to manufacture.

[0008]

A first structure of a differential amplifier circuit of the present invention which achieves the above object has a pair of differential transistors for receiving an input signal at their respective bases, In a differential amplifier circuit that amplifies and outputs a signal difference, the differential transistor pair is connected to a first constant current circuit with both emitters connected to each other, and the collector of one transistor has a second constant current circuit. A predetermined constant current is received via the collector-emitter of the output stage transistor of the current circuit, and the collector of the other transistor receives the collector-emitter of the output stage transistor of the second constant current circuit or the third constant current circuit. Receiving a predetermined constant current, the input side transistors are inserted and connected to the respective branch lines connected to the collector of the differential transistor pair. It detects respective varying current which comprises a Ntomira circuit flowing through the branch line, in which the amplified signal of the difference of the input signals from these variations current is obtained.

A second configuration of the differential amplifier circuit of the present invention which achieves the above object has a pair of differential transistors for receiving an input signal at their respective bases, and amplifies the difference between the input signals. In the differential amplifier circuit for outputting, in the differential transistor pair, both emitters are connected to each other and are connected to the first constant current circuit, and the collector of one transistor is the output stage transistor of the second constant current circuit. A predetermined constant current is received via a collector-emitter, and the collector of the other transistor receives the second constant current circuit or the third constant current circuit.
A current mirror circuit in which an input side transistor is inserted and connected between the collector of the differential transistor pair and a reference line, receiving a predetermined constant current through the collector-emitter of the output stage transistor of the constant current circuit Then, each fluctuating current branched and flowing out from the collector is detected, and the reversal current of the detected current is caused to flow from one line of the pair of power supply lines to the reference line, whereby the fluctuating current is A passive amplifier that obtains an amplified signal of the difference between the input signals, is connected between the one line of the power supply line and the reference line, and increases the current according to the increase of the voltage applied between them. Circuit and the current mirror circuit connected between the reference line and the other line of the power supply line to the reference line in a steady state. Potential of the reference line by including a fourth constant current circuit for supplying a total current of the total current of the currents and the current flowing to the passive circuit when the power supply voltage is the minimum operating voltage. Is to follow the potential of the one line of the power source line while maintaining a substantially constant difference.

[0010]

In the differential amplifier circuit according to the first aspect of the present invention, the single-stage output stage transistor of the constant current circuit, the differential transistor, and the constant current circuit are sequentially connected between the pair of power supply lines. In general, the voltage generated in the single-stage output stage transistor is smaller than the base-emitter voltage. Therefore, the voltage applied to the differential transistor has less voltage drop from the power supply voltage than the conventional one. In other words, the minimum operating voltage of the power supply voltage can be lowered by the difference. Further, since other circuits used for generating the output signal are general constant current circuits and current mirror circuits, the operation is stable and the manufacturing is easy.

Further, in the differential amplifier circuit of the present invention having the second structure, the single-stage output stage transistor of the constant current circuit, the differential transistor, and the constant current circuit are sequentially connected between the pair of power supply lines. Therefore, the minimum operating voltage of the power supply voltage is low. Moreover, since the other element circuits are general constant current circuits, current mirror circuits and passive circuits, the operation is stable even at a low voltage and the manufacturing is easy. Further, the potential of the first reference line, which provides the reference voltage of the current mirror circuit that detects the fluctuation current branched from the collector of the differential transistor, follows the power supply voltage while keeping a substantially constant difference.

As a result, the collector potential of the differential transistor also follows the power supply voltage while maintaining a substantially constant difference. Therefore, when the power supply voltage is high, the differential transistor can operate in a wide voltage range corresponding to the power supply voltage. That is, not only stable operation but also a wide dynamic range can be secured. Therefore, it is possible to operate stably even under a low power supply voltage, and it is possible to operate with sufficient performance even under a high power supply voltage.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment of the differential amplifier circuit of the present invention
The embodiment will be described with reference to the circuit diagram of FIG. Note that FIG. 2 is a specific example. Where Q1, Q
2 is a pair of differential transistors, Q11 and Q12,
Q21 and Q22, Q23 and Q24 form a current mirror, respectively. In the transistor Q1, the base receives one of the pair of input signals A, the emitter is connected to the constant current circuit (current value I1) together with the emitter of the transistor Q2, and the collector is the constant current I3 (note that I3 in FIG. 2 is I3).
= I1) is received. The difference between the collector current of the transistor Q1 and the constant current I3 is the current mirror (Q1) via the line branched from the collector of the transistor Q1.
1, Q12) and the reversal current is duplicated.

The transistor Q2 has a base for receiving the other signal B of the pair of input signals, and an emitter for the transistor Q2.
1 is connected to the constant current circuit (current value I1) together with the emitter, and the collector has a constant current I2 (where I2 = I in FIG. 2).
Receive 1). Then, the difference between the collector current of the transistor Q2 and the constant current I2 is caused by the current mirror (Q21, Q21,
Q22) and the reversal current is duplicated. This inversion current is inverted again by the current mirror (Q23, Q24).

In this way, the differential transistors (Q1, Q
The output stage circuit of the constant current circuit is connected upstream of 2). This output stage circuit may be a single-stage transistor in a constant current circuit using a current mirror circuit, for example (see FIG. 2). The voltage drop in the single-stage output stage transistor, that is, the collector-emitter voltage VCE is generally 0.
1 to 0.3V, which is smaller than the base-emitter voltage VBE of 0.6 to 0.7V. Therefore, the input stage transistor of the conventional current mirror is inserted and connected, and the voltage V
In the present invention, the voltage drop of BE is required, but in the present invention, the single-stage output stage transistor of the constant current circuit is connected, so that the voltage drop of VCE which is smaller than the conventional one is sufficient. Conversely, since a voltage drop other than that of the differential transistor is small, it is possible to operate in a lower power supply voltage. Further, since the constant current circuit and the current mirror circuit are used, the manufacturing is easy, and the operation of these is stable.

Under such a configuration, the transistor Q
1 controls the emitter current according to the input signal A, and the transistor Q2 controls the emitter current according to the input signal B. The sum of these emitter currents is kept constant (I1) by the constant current circuit downstream. Be drunk Therefore, when the emitter current via the transistor Q1 changes according to the input signal A, the emitter current via the transistor Q2 also changes in the opposite direction. Also, depending on the input signal B, the transistor Q
When the emitter current through 2 fluctuates, the transistor Q
The emitter current through 1 also fluctuates in the opposite direction. From this relationship, the emitter current through the transistors Q1 and Q2 fluctuates in the opposite direction according to the difference between the input signals A and B.

Further, since the emitter current through the transistor Q1 is almost equal to the collector current, the variation of the emitter current is expressed as a difference current with the constant current I3, so that the transistor Q is changed.
This is reflected in the current (fluctuation current) to the branch line connected to the collector side of 1. This is the current mirror (Q11,
It is described above that it is detected by Q12). On the other hand, since the emitter current through the transistor Q2 is almost equal to the collector current, the variation of the emitter current is also the constant current I.
A difference current with respect to 2 is reflected in the current (fluctuation current) to the branch line connected to the collector side of the transistor Q2. This is the current mirror (Q21, Q22), (Q2
3, Q24).

Then, a current signal consisting of the difference between the duplicated fluctuating currents is output as the output signal C to the output line branched from the connection point between the transistor Q24 and the transistor Q12. As described above, the transistor Q1,
Since the fluctuation of the current through Q2 fluctuates in the opposite directions, the difference current of this fluctuation current is
The fluctuation of the current through 2 is doubled. Therefore, the output signal C is obtained by amplifying the difference between the input signals. That is, this circuit can operate normally even under a low power supply voltage.

Further, FIG. 3 shows a circuit diagram as a second embodiment of the present invention. Note that FIG. 4 is a specific example. This circuit is an improvement of the invention of the first embodiment described above, and its essential part, that is, the differential transistor pair (Q1,
The same applies to Q2), the constant current circuit, the detection current mirror, and the like. The difference is that the detection current mirror group is not provided between the pair of power supply lines but is provided between one line (Vcc) of the pair of power supply lines and the reference line 100 of the intermediate potential. It is that you are. Further, a passive circuit including a resistor R1 and a diode D3 connected in series is added between the line (Vcc) and the reference line 100 in parallel with the detection current mirror group.
A constant current circuit (current value I4) is added between 0 and the other line (GND) of the pair of power supply lines.

The current value I4 is the total current of the currents flowing through the reference line 100 in the steady state of the current mirror group (Q11, Q12, Q21, Q22) and the passive circuit (when the power supply voltage is the minimum operating voltage). R1 and D3) are set to the total current value including the current flowing in. Passive circuit (R
1, D3), the current flowing in this circuit alone
It is determined corresponding to the voltage between the power supply line (Vcc) and the reference line 100, and the current increases as the voltage increases.

On the other hand, the current flowing through the current mirror group is
It is the remainder obtained by subtracting the constant current I1 from the sum of the constant current I3 and the constant current I2, which is constant. Therefore, the current flowing through the passive circuits (R1, D3) incorporated in the entire differential amplifier circuit is the rest of the constant current I4 minus the current flowing through the current mirror group due to the restriction of the constant current I4. It is constant. By the way, as described above, the current value I4 is originally set to the total current value of the current in the current mirror group and the current flowing in the passive circuits (R1, D3) when the power supply voltage is the minimum operating voltage. . For these reasons, the voltage between the power supply line (Vcc) and the reference line 100 is kept constant.

That is, the potential of the reference line 100 is controlled by the constant current circuit (I4), and the potential of the reference line 100 follows the potential of the power supply line (Vcc) while maintaining a substantially constant difference. When the potential of the reference line 100 maintains a constant difference with respect to the potential of the power supply line (Vcc), the transistors Q1 and Q2 having a potential higher than the potential of the reference line 100 by the drop voltage VBE at the input stage transistor of the current mirror. The collector potential also holds a substantially constant difference with respect to the potential of the power supply line (Vcc).

As a result, when the power supply voltage Vcc is high, the collector-emitter voltage of the transistors Q1 and Q2 can be ensured at a sufficiently high voltage which is almost equal to the power supply voltage Vcc. Therefore, the input signals A and B can take values within this voltage range. That is, in addition to stable operation under a low power supply voltage, it is possible to operate with a wide dynamic range secured under a high power supply voltage. It should be noted that this circuit does not require a special element or the like, and the diode D3 can be a diode-coupled one of a general transistor, so that the manufacturing is easy.

[0024]

As can be understood from the above description, the differential amplifier circuit of the present invention is stable even under a power supply voltage which is low by the difference between the collector-emitter voltage and the base-emitter voltage. Can be operated in a stable manner under a low power supply voltage or a high power supply voltage without impairing the dynamic range, and since it is composed of a general transistor circuit, the semiconductor manufacturing process can be improved. There is an effect that manufacturing is easy without any restriction.

[Brief description of drawings]

FIG. 1 is a first diagram of a differential amplifier circuit having a configuration of the present invention.
3 is a circuit diagram of the embodiment of FIG.

FIG. 2 is a detailed circuit diagram of the specific example.

FIG. 3 is a second diagram of the differential amplifier circuit having the configuration of the present invention.
3 is a circuit diagram of the embodiment of FIG.

FIG. 4 is a detailed circuit diagram of the specific example.

FIG. 5 is an example of a conventional differential amplifier circuit.

FIG. 6 is another example of a conventional differential amplifier circuit.

[Explanation of symbols]

 100 reference line Q1, Q2 differential transistor

Claims (2)

[Claims] 1. A differential amplifier circuit having a pair of differential transistors at respective bases for receiving an input signal and amplifying and outputting a difference between the input signals, wherein the differential transistor pair has both emitters. Are connected to each other and connected to the first constant current circuit, the collector of one transistor receives a predetermined constant current through the collector-emitter of the output stage transistor of the second constant current circuit, and the collector of the other transistor Receives a predetermined constant current through the collector-emitter of the output stage transistor of the second constant current circuit or the third constant current circuit, and connects to each branch line connected to the collector of the differential transistor pair. On the other hand, a current mirror circuit in which an input side transistor is inserted and connected is provided, and each fluctuating current flowing in the branch line is detected. Differential amplifier circuit, characterized in that the amplified signal of the difference between the input signals from these variations current is obtained. 2. A differential amplifier circuit having a pair of differential transistors at respective bases for receiving an input signal and amplifying and outputting a difference between the input signals, wherein the differential transistor pair has both emitters. Are connected to each other and connected to the first constant current circuit, the collector of one transistor receives a predetermined constant current through the collector-emitter of the output stage transistor of the second constant current circuit, and the collector of the other transistor Receives a predetermined constant current through the collector-emitter of the output stage transistor of the second constant current circuit or the third constant current circuit, and the input side is provided between the collector and the reference line of the differential transistor pair. A current mirror circuit in which a transistor is inserted and connected is provided, and each variable current branched and flowing out from the collector is detected and detected. By flowing an inversion current of the current from one of the pair of power supply lines to the reference line, an amplified signal of the difference between the input signals is obtained from these fluctuating currents, and the one of the one of the power supply lines is A passive circuit that is connected between a line and the reference line and has a current that increases in response to an increase in voltage applied between the line and the reference line, and is connected between the reference line and the other line of the power supply line. A fourth constant current that flows a total current of the total current that flows in the reference line in a steady state of the current mirror circuit and the current that flows in the passive circuit when the power supply voltage is the minimum operating voltage. A differential amplifier circuit, wherein the potential of the reference line follows the potential of the one line of the power supply line while maintaining a substantially constant difference.