JPS62243408A - Differential amplifier circuit - Google Patents

Abstract

PURPOSE:To obtain a differential amplifier operated at a low voltage and having a large dynamic range by using a differential pair comprising transistors(TR)Q1, Q2 as a building block and providing four current mirror circuits as active loads, resistors, constant current sources and bias power supplies. CONSTITUTION:The current mirrors 13-16 and resistors R1-R4 are connected to the building block comprising TRs Q1, Q2 and bias voltage source 8, 10, 11 and constant current sources 12, 18 are connected as specified. A reference voltage A reaches a bias voltage E1-I0R2 at a connecting point P1 between elements Q3, Q7, that is, at an inverting output terminal 6 by a constant current I0. In selecting the reference voltage A as a power supply voltage Vcc/2, the maximum amplitude at the output B is Vcc-2VCE, where VCE is the saturated voltage of the TRs, which is a very large value. Further, the gains G are respec tively G=v1/v0=R3/R1 and G=v2/v0=R2/R1, where v1, v2 are outputs at the terminals 5, 6 and v0 is an AC input, and in selecting the resistors R1-R3 equal, the outputs of the terminals 5, 6 are synchronized with the input and the outputs whose phase is inverted and whose amplitude is equal are obtained.

Description

Detailed Description of the Invention [Industrial Application Field of the Invention] The present invention is a differential amplifier circuit that operates at a low voltage (reduced voltage of about 0.9 V), has a large input/output dynamic range, and has an inverting The present invention relates to a differential amplifier circuit having an output terminal and a non-inverting output terminal.

[Problem that the invention seeks to solve]

A conventional differential amplifier circuit will be explained based on FIG. 5.

Such a differential amplifier circuit is based on a differential pair consisting of transistors Q1 and Q2, and has two current mirror circuits consisting of a diode D1 and a transistor Q3 as an active load circuit, and a diode D2 and a transistor Q5, and a resistor R4. is added. An AC signal S is superimposed on the DC voltage El of the bias voltage source 10 and applied to the base of the transistor Q1 via the non-inverting input terminal 3, and a load current (mirror current) is applied to the base of the transistor Q7 and the current mirror circuit, respectively. Current consisting of diode D4
The transistor Q is supplied to the mirror circuit.
3 and Q7 is a non-inverting output terminal 9, a resistor RIO and a bias voltage source 8 are connected in series between the base of the transistor Q2 and the ground terminal 2, and a feedback resistor is connected between the base of the transistor Q2 and the output terminal 9. R20 is connected.

However, such non-inverting differential amplifier circuits are less than IV (
If you try to operate with a low power supply voltage VCC with a reduced voltage of 0.9V, the input/output dynamic range is small and it will not work with large amplitude AC input signals, or it will cause distortion. This will be explained based on FIG. In order to bias transistor Q1, the base-emitter voltage Via (approximately 0.6
8V) must be applied.

Therefore, the bias voltage El is set to a voltage of about 0.7 V, and the alternating current signal S is superimposed on the bias voltage E and applied to the base of the transistor Q1. The signal S has an amplitude based on the potential of the bias voltage El, and the amplitude voltage is equal to the base-emitter voltage Vat of the transistor Q1 (approximately 0.
68V).

That is, the input dynamic range is at most 0.04Vp-
p, and if a signal S with an amplitude larger than this value is input, distortion will occur, which is not preferable.

Therefore, at low voltages, it is impossible to increase the input dynamic range with a differential amplifier circuit in which a signal is directly applied to the base of transistor Q1.

With such an unpowered differential amplifier circuit, it is difficult to obtain two kinds of outputs, one in phase and the other in phase with respect to the phase of the input signal.

[Purpose of the invention]

The differential amplifier circuit according to the present invention was made to improve the above-mentioned problems, and its main purpose is to provide a differential amplifier circuit that operates stably at a low voltage of 1 V or less (reduced voltage of 0.9 V). The purpose of the present invention is to provide dynamic amplification circuits.

Another object of the present invention is to provide a negative feedback type differential amplifier circuit with a large input/output dynamic range.

Still another object of the present invention is to provide a differential amplifier circuit capable of obtaining two types of outputs whose phases are inverted from each other.

[Embodiments of the invention]

FIG. 1 is a circuit diagram showing an embodiment of a differential amplifier circuit according to the present invention.

In the figure, 1 is a power supply terminal, 2 is a ground terminal, 3 is an input terminal to which bias voltage E is supplied, and 4 is bias voltage E.
an input terminal to which an AC input signal S is superimposed and applied to l;
5 is an output terminal for obtaining a non-inverted output, 6 is an output terminal for obtaining an inverted output, 13 to 16 are first to fourth current mirror circuits, 8°10.11 is a bias voltage source, 12.18
is a constant current source circuit. The power supply voltage vcc is set to approximately IV (reduced voltage 0.9V), and the bias voltage B is approximately 0.7V.
and bias voltage ES to Vcc/2.

In such a differential amplifier circuit, an AC input signal V is superimposed on a bias power supply El and applied from an input terminal 4, and current mirror circuits 13 and 14 output mirror currents (I-Δl) and (1+Δi), respectively. ) is assumed to flow transiently. ! indicates a DC radio wave component, and the DC component I
I = (E+Vmi) / R4...i
It is represented by ll. In addition, Δi indicates a signal current component, and the signal current component Δi is expressed as Δi −1/2 ・vo / R1=−(21).Furthermore, it is applied to the diode D4 via the current mirror circuit B14. Since a mirror current of (I + Δi) flows as a forward current, the collector current of the transistor Q7 in the output stage of the current mirror circuit 15 is (I +
A current of Δi) is about to flow. Also, from the transistor Q3 of the output stage of the current mirror circuit 13 (■-Δi)
Since a mirror current of
A current of Δi flows. Therefore, the negative feedback resistor R2 has 2
A voltage drop of Δ5-R2 will occur.

On the other hand, a forward current (
A mirror current of I-Δi) is supplied. Also, the current
Through the transistor Q6 of the output stage of the mirror circuit 14 (
A mirror current of I+Δi) flows. Since the transistor Q8 forms the current mirror circuit 16 together with the diode D3, a current of (I-Δi) tends to flow as the collector current of the transistor Q8. Therefore, transistor Q8 is (I+Δi) from transistor Q6.
Since the mirror current of R3 is supplied, at the 22nd point, the resistor R3
A current of 2Δi will be applied to. Therefore, the resistance R
3, a voltage drop of 2Δ1-R3 is generated, and an output in which a voltage of 2Δ1-R3 is superimposed on the bias voltage E2 is output from the non-inverting output terminal 5. Bias voltage source E2 is El
/2 value.

Next, the input/output dynamic range of such a differential amplifier circuit will be explained with reference to FIG.

Constant current 1 from the constant current source circuit 17. is injected into the negative feedback resistor R2, so ′ between the terminals of the negative feedback resistor R2 is
, · A voltage drop occurs across R2. Therefore, transistor Q
The potential at the connection point P1 between Q3 and Q7 is lower than the bias voltage E by the value of Io·R2. Therefore, at the inverting output terminal 6, the reference voltage potential (A) is (E I
t.・R2) value, and the reference potential (a) becomes Vcc/2
If set to , the maximum amplitude voltage of the output (b) will be 2 V
This is the value obtained by subtracting the value of C, that is, the input/output dynamic range becomes the value of (Vcc 2 VC - VP-P), which is extremely wide (can be set).

Incidentally, assuming that the AC input voltage of the differential amplifier circuit is vo and the output from the non-inverting output terminal 5 is vl, the gain G of the differential amplifier circuit is expressed by the following equation.

G=Vt/Vo=R3/R1--(
3) Furthermore, if the output from the inverting output terminal 6 is v2, its gain G is expressed as in the following equation.

Gxv, /v6 = R2/R1...-r4 Therefore, if the resistance values of resistors R1 to R3 are set equal, the output derived from the inverting output terminal 6 and the non-inverting output terminal 5 will be equal to the input signal. It is possible to derive outputs having equal amplitude voltages with mutually inverted phases.

Next, another embodiment of the present invention will be described based on FIG. 2. In the embodiment shown in FIG. 2, the constant current source circuit 19 is configured to draw a constant current I0 from the connection point P2,
The other circuits are the same as the embodiment shown in FIG. Also, constant current source 1
The constant current from 2 and the current flowing through the emitter resistor R4 are 1.
This is an example of setting.

An AC input signal v0 is applied from input terminal 4 to the base of transistor Q2 via resistor R1. Further, a constant current I0 is supplied from the constant current source circuit 12 to the negative feedback resistor R2. Therefore, the current mirror circuits 13 and 14 have −(Δi+Ie/2
), a mirror current of (Δi+10/2) flows. The collector current of transistor Q3 is −(Δi+7°/
2) flows, and a mirror current of (Δl + re/2) flows from the transistor Q5 of the current mirror circuit 14 to the diode D4, so a current of (Δi+l./2) flows as the collector current of the transistor Q7. flows. Therefore, a current of (2Δi+10) will flow through the negative feedback resistor R2, and a voltage drop of R2·(2Δi+l.) will occur between the terminals of the negative feedback resistor R2. Therefore, the inverting input terminal 6 has E+R2.
An output voltage of (2Δi'+70) will be generated.

On the other hand, a mirror current of (Δi×./2) flows from the transistor Q6 of the current mirror circuit 14. A mirror current of -(Δi+ to/2) is output from the transistor Q4 of the current mirror circuit 13 as a mirror current.
Since the current flows through the diode D3, a current of -(Δ1+1°/2) tends to flow as the collector current of the transistor Q8. Therefore, from the 22 points to the non-inverting output terminal 5 (2
A current of Δi+(.) flows. Also, a constant current source circuit 19 generates a constant current ■. Because it is designed to attract
A current of 2Δl flows through the resistor R3. Therefore, an output voltage of (E!2Δ1-R3) is generated between the non-inverting output terminal 5 and the ground.

FIG. 4 is a circuit that more specifically embodies the embodiment of the differential amplifier circuit shown in FIG. 2 according to the present invention, and is a constant current source circuit 12.19.
is shown using a current mirror circuit. The other circuits are the same as in FIG.

Note that various known circuits may be applied to the current mirror circuits 13 to 16 without being limited to the embodiments.

〔Effect of the invention〕

As described above, the differential amplifier circuit of the present invention can extremely widen the input/output range, and can provide a differential amplifier circuit that operates at a reduced voltage of 0.9V.

For example, if the power supply voltage VCC is 0.9V, the saturation voltage VC of the transistor! If it is about 0.2V, the two-person output range can be expanded to about 0.5V-r. In addition, it is extremely effective in that it is possible to obtain two types of outputs that are inverted from each other with one differential amplifier circuit, rather than the conventional method where two differential amplifier circuits are provided and two types of outputs that are inverted from each other are obtained. It is.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the differential amplifier circuit according to the present invention, and FIG. 2 is a circuit diagram showing another embodiment of the differential amplifier circuit according to the present invention. FIG. 4 is a diagram for explaining the input/output range of the differential amplifier circuit according to the invention, and FIG. 5 is a circuit diagram showing a more specific differential amplifier circuit of the embodiment of FIG. 2. is a circuit diagram showing a conventional differential amplifier circuit, and FIG. 6 is a waveform diagram for explaining its input dynamic range. 1: Power supply terminal, 2: Ground terminal, 3.4: Input terminal 5: Non-inverting output terminal, 6: Inverting output terminal, 8゜10.11: Bias voltage source, 13 to 16゜19: Current mirror circuit, 12. 18. 19: Current source circuit, S
:Input signal source

Claims (3)

[Claims] (1) A resistor is connected to the commonly connected emitters of the first and second transistors forming a differential pair, and first and second current mirrors are connected to the collectors of the first and second transistors, respectively. An active load circuit consisting of a circuit is connected, and the first
and a first output stage transistor of each of the first and second current mirror circuits are connected to a third current mirror circuit; A transistor of the output stage is connected to a fourth current mirror circuit, and a first current mirror circuit of the first current mirror circuit is connected to the output stage transistor.
A connection point P1 between the transistor of the output stage and the transistor of the third current mirror circuit is an inverting output terminal,
The connection point P2 between the transistor of the second output stage of the second current mirror circuit and the transistor of the fourth current mirror circuit is a non-inverting output terminal, and the signal input terminal and the base of the second transistor are connected to each other. A first resistor is connected between the base of the second transistor and the inverting output terminal, a second resistor is connected between the base of the second transistor and the inverting output terminal, and a third resistor is connected to the non-inverting output terminal.
A resistor is connected to the other end, a bias voltage source is connected to the other end, and a constant current source circuit is connected to the connection point between the first resistor and the second resistor. The second
A differential amplifier circuit characterized in that the input/output dynamic range is expanded by supplying a constant current to the resistor to reduce the DC level of the output obtained from the inverting input terminal. (2) In the differential amplifier circuit, a current equal to the constant current supplied to the second resistor is drawn from the other end P1 of the second resistor. The differential amplifier circuit described. (3) A patent claim in which the differential amplifier circuit includes a current source that draws a current equal to the current supplied from the constant current source circuit to a connection point between the second and fourth current mirror circuits. 1. The differential amplifier circuit according to item 1.