JP2002111409A - Differential amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement a differential amplifier which does not cause a phase inversion of an output and requires shorter time for returning from saturation to active conditions. SOLUTION: The differential amplifier comprises a pair of transistors; a collector resistor and an emitter resistor connected to the pair of transistors respectively; a differential amplifier circuit comprising a constant power source commonly connected to the pair of transistors through the emitter resistor; a first transistor of which collector is connected to a base of one of the pair of transistors, and of which base is connected to an emitter of one of the transistors; a second transistor of which collector is connected to a base of the other of the pair of transistors, and of which base is connected to the emitter of the other of the transistor; a pair of constant power sources connected to the collectors of the first and second transistors for respectively for supplying power; and a pair of transistors of a first stage connected to each emitter of the first and second transistors for amplifying differential input signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential amplifier, and more particularly to an improvement for eliminating a phase inversion of an output at the time of an excessive input and shortening a recovery time.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a conventional differential amplifier used for an input circuit or the like of a measuring instrument. The differential amplifier is roughly a portion consisting of NPN transistors Q1 and Q2 and the constant current source I _1, and NPN transistors Q4 Q5,
A portion comprising a resistor R2~R5 and a constant current source I _2, N
It consists portion consisting of PN transistors Q6 and Q7 and a constant current source I _3, respectively each of these parts has a differential amplifier circuit. A power supply voltage (V _CC on the high voltage side and V _EE on the low voltage side) is applied to these differential amplifier circuits.

A constant current source composed of a depletion type P-channel MOSFET Q3 and a resistor R1 acts as a load for the transistor Q2, while a constant current source composed of a depletion type P-channel MOSFET Q8 and a resistor R6 is connected to a transistor Q6. Load.

Further, the differential input voltage V _i1 and V _i2 are applied to the bases of the transistors Q1 and Q7, the differential output V ₀₁ and V ₀₂ is taken from the collectors of the transistors Q4 and Q5.

The base of the transistor Q4 is connected to the transistor Q of a differential amplifying circuit comprising
2 and the emitter of Q4 is connected to the base of the same transistor Q2, so that negative feedback is applied. Therefore, the linearity with respect to the signal applied to the base of the transistor Q1 is improved.

The same can be said for the transistor Q5. For this reason, the transistors Q4 and Q5 equivalently have a large transconductance (gm). If the gain of this circuit is R2 = R4 and R3 = R5, R2 / R3
Becomes

[0007]

By the way, when a differential amplifier having such a configuration is used for an input circuit of a measuring instrument or the like,
There were the following problems with excessive input. (1) When the base potential of the transistor Q1 and Q7 rises to the vicinity of the power supply V _CC of the circuit, the phase of the output of the amplifier will the transistor Q4 and Q5 is saturated is inverted. (2) It takes time for the bipolar element to return from the saturated state to the active state.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem, and without causing the above-described phase inversion of the output.
Further, it is an object of the present invention to provide a differential amplifier having a short recovery time for returning from a saturated state to an active state.

[0009]

In order to achieve the above object, according to the present invention, a pair of transistors, a collector resistor and an emitter resistor respectively connected to the pair of transistors, and the emitter resistor are provided. A differential amplifier circuit composed of a constant current source commonly connected to the pair of transistors, and a collector connected to a base of the pair of one transistors and a base connected to an emitter of the one transistor A first transistor, a second transistor having a collector connected to the base of the other pair of transistors and a base connected to the emitter of the other transistor, and collectors of the first and second transistors. A pair of constant current sources connected to each supply current, and the first and second transistors; And a pair of first-stage transistors connected to each emitter of the data amplifier and amplifying the differential input signal.

With such a configuration, even if an excessive voltage is applied to the differential input, the bipolar transistors Q4 and Q5 can be prevented from being saturated.

In this case, a depletion-type P-channel MOSFET, a P-channel JFET, or a PNP-type bipolar junction transistor can be used as the pair of first-stage transistors.

According to a third aspect of the present invention, the pair of constant current sources respectively connected to the collectors of the first and second transistors are a depletion-type P-channel M-channel transistor.
It can be composed of an OSFET or a P-channel JFET and a resistor.

Furthermore, by connecting a pair of diodes in anti-parallel between the emitters of the first and second transistors, the first-stage transistor can be connected when the differential input voltage becomes excessive. Can be protected.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the differential amplifier according to the present invention. In the figure, parts that are the same as those in FIG. 2 are given the same reference numerals, and descriptions of the connections and the like are omitted. Incidentally, FIG. 2 differs from the the transistor Q1 and Q7 and the constant current source I ₁ and I ₃ are deleted, Q10 and Q1
1 and D1 and D2 are added.

Q10 and Q11 are depletion type P-channel MOSFETs, and Q10 is a transistor Q
2 (herein, the transistor Q2 is referred to as a first transistor for convenience) is connected between the emitter of the transistor Q2 and the low-voltage side power supply,
Q11 is connected between the emitter of the transistor Q6 (here, the transistor Q6 is referred to as a second transistor for convenience) and the low-voltage side power supply. Differential input voltages _Vi1 and _Vi2 are applied to the gates of Q10 and Q11, respectively. D1 and D2 are protection diodes that are turned on when the differential input voltage becomes excessive.
Are connected in anti-parallel between the emitters.

A portion comprising NPN transistors Q4 and Q5, four resistors R2 to R5 and a constant current source I2 constitutes a differential amplifier circuit as in FIG. And MOSFET Q
Numeral 10 is a source follower, and the NPN transistor Q2 is a kind of grounded base circuit, which passes the output of the MOSFET Q10 to the transistor Q4 and applies a negative feedback to the transistor Q4 to improve the linearity.

Also, a depletion type P channel
MOSFET Q11 is also a source follower, and N
PN transistor Q6 is a kind of grounded base circuit,
The output of the MOSFET Q11 is passed to the transistor Q5 and negative feedback is applied to the transistor Q5 to improve the linearity.

Since transistors Q2 and Q6 apply negative feedback to transistors Q4 and Q5, respectively.
Q4 and Q5 equivalently have a large mutual conductance (gm). Therefore, the gain of this circuit is R2 = R4
If R3 = R5, then R2 / R3.

In such a configuration, when an excessive input is applied and the gate potential of MOSFET Q10 approaches V _CC , the following occurs. Q10 is depletion type P
Since this is a channel MOSFET, the source potential is lower than the gate potential. In this case, the source potential of Q10 is lower than the V _CC voltage by the voltage drop at the resistor R1, the drain-source voltage of Q3, and the Q2 and Q4. Base-emitter voltage V
Since the voltage is kept low by the sum of be and Q4, Q4 does not saturate.

Since Q11 is also a depletion type P-channel MOSFET, the transistor Q5 does not saturate for the same reason as described above.

Further, if the gate potential of MOSFETQ10 is close to V _EE, Q10 is cut off, the diode D1 is turned on, and Q2 for passing a current of the constant current source consisting of Q3 and R1 to Q11 Q4 does not saturate. When the gate potential of the likewise Q11 is close to V _EE is also Q5 and Q6 not saturated.

The present invention is not limited to the above-described embodiment, but includes many more changes and modifications without departing from the essence thereof.

For example, the constant current sources Q3 and Q8 are not limited to P-channel MOSFETs, but may be P-channel JFETs or PNP type bipolar junction transistors (BJs).
T). Also, Q10, Q11 of the first stage
Similarly, a transistor such as a P-channel JFET or a PNP type BJT may be used.

[0024]

As described above, according to the present invention, a differential amplifier which does not saturate a bipolar element with respect to an excessive input, does not cause a phase inversion of an output, and has a short recovery time can be easily realized. be able to.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram illustrating an example of a conventional differential amplifier.

[Explanation of symbols]

Q2, Q4, Q5, Q6 transistors Q3, Q8, Q10, Q11 MOSFET R1~R6 resistance D1, D2 diode I ₂ constant current source

Claims (4)

[Claims] 1. A differential amplifier comprising a pair of transistors, a collector resistor and an emitter resistor respectively connected to the pair of transistors, and a constant current source commonly connected to the pair of transistors via the emitter resistor. A circuit, a first transistor having a collector connected to the base of one of the pair of transistors and a base connected to the emitter of the one transistor, and a collector connected to the base of the other transistor of the pair. A second transistor having a base connected to the emitter of the other transistor, a pair of constant current sources connected to collectors of the first and second transistors and supplying currents, respectively; Connected to each emitter of a pair of transistors to amplify the differential input signal. Comprises a transistor, a differential amplifier, characterized by being configured such that an output corresponding to obtain the differential input signal from the collector of a pair of transistors of the differential amplifier circuit. 2. A depletion type P-channel MOSFET or P-type MOSFET as said pair of first stage transistors.
2. The differential amplifier according to claim 1, wherein a channel JFET or a PNP type bipolar junction transistor is used. 3. A pair of constant current sources respectively connected to the collectors of the first and second transistors are composed of a depletion type P-channel MOSFET, a P-channel JFET or a PNP type bipolar junction transistor, and a resistor. 2. The differential amplifier according to claim 1, wherein: 4. The differential amplifier according to claim 1, further comprising a pair of diodes connected in anti-parallel between the emitters of said first and second transistors.