JPS593606Y2 - Complementary differential amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a differential amplifier circuit having complementary characteristics.

A conventional example is shown in FIG. In the figure, NPN transistors 3 and 4 and PNP transistor 5 have complementary characteristics.
, 6 are NPN) transistors 3 and P
NP) transistor 5 and NPN transistor 4 and PNP
) transistors are commonly connected and connected to input terminals 1 and 2, NPN) transistors 3 and 4 and PNP)
The collectors of transistors 5 and 6 are connected to the emitters of NPN) transistors 8 and PNP) transistors 9 and 10, respectively, and the emitters are connected in common, and the negative power supply (-B) and positive Connected to power supply (10B).

The collectors of transistors 7 and 8 and 9 and 10 are connected to a positive power supply (10B) and a negative power supply (-B) via resistors 11 and 12 and 13 and 14, respectively, and the bases of transistors 7 and 8 are commonly connected. together with resistor 17 and constant voltage element 1
The bases of transistors 9 and 10 are connected in common, and the resistor 20
and is connected to the negative power supply (-B) and ground via the constant voltage element 19.

In the above configuration, differential transistors 3 and 4 and 5 and 6
Since the collector voltage of is determined by the constant voltage elements 18 and 19, the maximum allowable input level of the input signals applied to the input terminals 1 and 2 is restricted by the voltages of the constant voltage elements 18 and 19.

Therefore, the voltage of the constant voltage element is generally set to about 10 to 20 V in consideration of the magnitude of the input signal level, so when the signal source impedance connected to input terminals 1 and 2 is high, the collector cutoff current ( IcB.

) becomes a non-negligible level, causing problems such as temperature drift, and the differential transistors 3, 4, 5, and 6 self-heat due to the collector voltage and current, and temperature drift occurs due to this heat generation. Since the collector-base voltage of a differential transistor changes approximately equal to the input signal level, when the signal source impedance is high, a mirror effect occurs due to the transistor's collector-base junction capacitance (Cob), which also causes deterioration of high-frequency characteristics. become.

The present invention has a simple circuit configuration, and the collector interrupting current (ICB)
This invention provides a low distortion amplifier that has little drift due to factors such as O) and a large allowable input signal level.
The figure shows an embodiment of the present invention.

In the figure, the bases of a PNP) transistor 22, an NPN) transistor 23, a PNP) transistor 26, and an NPN) transistor 27, which have complementary characteristics, are symmetrically connected in common and connected to input terminals 1 and 2, and the emitters are connected to the positive power supply (10B) and the negative power supply (-B) via constant current sources 21 and 24 and 25 and 28, respectively, and are connected to the NPN) transistor 3 and the PNP) transistor 5.
and NPN) transistor 4 and PNP) transistor 4 are connected to their respective bases.

Emitters of transistors 3 and 4 and transistors 23 and 2
The collectors of transistors 7 and 7 are commonly connected, the emitters of transistors 5 and 6 and the collectors of transistors 22 and 26 are commonly connected, and the collectors of transistors 3 and 4 and 5 and 6 are connected to the positive power supply through resistors 11 and 12 and 13 and 14, respectively. (10B
) and the negative power supply (-B).

In the above configuration, the emitter follower transistor 22
．． The operating currents of 23, 26, and 27 are determined by constant current sources 21, 24, 25, and 28, each having an equal current value (■0), and have the same current value (■0).

The operating currents of the differential amplification transistors 3 and 4 and 5 and 6 are the sum of the current values of constant current sources 24 and 28 and the sum of the current values of constant current sources 21 and 25, respectively, and
Since the characteristics of 4, 5, and 6 are the same, 1/2 of the sum of the current values (2・Io) of the constant current sources flows, and the operating currents of transistors 3, 4, 5, and 6 are constant currents. It becomes equal to the source current value (■0).

The collector-base voltages of transistors 22 and 26 and 23 and 27 are approximately OV since their respective collectors are connected to the common emitter terminals of transistors 5 and 6 and 3 and 4.

Next, when a positive input signal is applied to input terminal 1 while input terminal 2 is grounded, the emitter potentials of transistors 22 and 23 rise, the current of transistor 3 increases, and the current of transistor 5 decreases. .

At the same time, the current in transistor 4, which is differentially connected, decreases, and the current in transistor 6 increases.

Therefore, negative and positive differential outputs are generated at the collectors of transistors 3 and 4 and 5 and 6, respectively, and the outputs of transistors 3 and 4 and 5 and 6 have complementary characteristics.

Also, when a positive input signal is applied to input terminal 2 while input terminal 1 is grounded, transistors 3 and 4 are connected in the same way as described above.
Positive and negative differential outputs are generated at the collectors of transistors 3 and 5 and 6, respectively, and the outputs of transistors 3 and 4 and transistors 5 and 6 have complementary characteristics.

Therefore, when input signals of the same phase and level are applied to the input terminals 1 and 2, no output is generated at the collectors of the transistors 3, 4, 5, and 6.

In this way, the outputs of transistors 3 and 4 and 5 and 6 are differential outputs, and the outputs of transistors 3 and 4 and 5 and 6 provide complementary push-pull outputs with complementary characteristics, which are connected to the next stage. Complementary push-pull circuits can be easily driven and therefore have low distortion.

Next, the collector potentials of transistors 22, 26 and 23, 27 are equal to their respective base potentials, and the collector-base voltage is always kept at a constant level, approximately Ov, regardless of the magnitude of the input signal.

Therefore, even if the signal source impedance connected to input terminals 1 and 2 is high, transistors 22, 26 and 23
．． Since the mirror effect due to the collector-base junction capacitance (Cob) of No. 27 does not occur, there is no deterioration of high frequency characteristics.

Further, the voltage applied between the collector and emitter of the transistor 22, 26, 23, 27 is about 0.6 V, and self-heating is extremely small.

Although the collector-base voltages of transistors 3, 4 and 5, 6 vary greatly depending on the input signal, the input circuit of each transistor is composed of transistors 22, 26, 23, .
27 emitter followers are connected, and the output impedance of the emitter followers is a very low value and no mirror effect occurs.

Therefore, similarly to the above, deterioration of high frequency characteristics does not occur.

Next, the effect of the collector cut-off current (ICBO) of the transistor is the emitter follower transistor 22°2B,
Since the collector-base voltage of 23.27 is approximately Ov, no collector cut-off current (ICBO) flows, and of course no temperature drift occurs, and the differential amplifier transistor 3.4
,5. Although a high voltage is applied to the collector-base voltage of , e, the output impedance of the emitter follower connected to each input circuit is extremely low, so even if there is a slight collector-blocking current (ICBO), there is no problem. Of course, there is no problem even if the collector cut-off current (ICBO) drifts with temperature.

Next, the effect of temperature drift on the VBE of the transistors is as follows:
Since the transistors are connected in such a direction that the VBE of 27V is canceled out, if the characteristics of the transistors of the same conductivity type and the complementary transistors are the same, even if the VBE of each transistor drifts with temperature, there will be no fluctuation due to the drift.

As described above, according to the present invention, it is possible to provide a low distortion amplifier with a simple circuit configuration, good DC stability, no deterioration of high frequency characteristics, and a large allowable input signal level.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional example, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. 1, 2 are input terminals, 3, 4.7, 8.23.27 are N
PN) transistor, 5°6, 9.10.22.26 is P
NP) transistor, 11.12゜13, 14 is load resistance, 15.16.21.24.25.2B is constant current source, 1
8.19 is a constant voltage diode.

Claims (1)

[Scope of utility model registration request] A first transistor comprising transistors of first and second conductivity types.
and an emitter follower constituted by a transistor of a second conductivity type and a first conductivity type driven by a constant current source is connected to each input circuit of the second complementary differential amplifier circuit, and the conductivity type constituting each emitter follower is connected to each input circuit of the second complementary differential amplifier circuit. Corresponding input circuits of different transistors are connected in common, and the collectors of the transistors of the first conductivity type constituting the emitter follower are connected to the emitter of the first differential amplifier circuit. 1. A complementary differential amplifier circuit, characterized in that collectors of transistors of a second conductivity type constituting the emitter follower are connected to an emitter of the amplifier circuit.