JPS63185208A - Differential amplifying circuit - Google Patents

Abstract

PURPOSE:To suppress the variance of gain caused by the variance of a value of resistance of an integrated circuit, by providing an error amplifying for comparing the same phase output voltage and a reference voltage, detecting an error from a prescribed value of a current quantity of a constantcurrent source, and executing a negative feedback control so that said current quantity becomes the prescribed value. CONSTITUTION:The same phase output voltage detecting resistances 14, 15 which have eliminated a constant-voltage source in a conventional circuit, and in which a constant-voltage source 16 and one end are connected to an output terminal 4 and 5, respectively, and the other end is connected in common at a point A, and an error amplifier 17 in which an inversion input is connected to the constant-voltage source 16, and a non-inversion input is connected to the point A, and an output is connected to a base of a transistor 8 are added. In this case, a resistance value RA of the resistances 14, 15 is higher enough than a resistance value RL of resistances 11, 12. A voltage of the connecting point A is a voltage which has divided a voltage of output signals whose phases are opposite to each other, into two, and becomes equal to the same phase output voltage of a differential amplifying circuit. The potential of the point A is compared with a reference voltage VR, and by an output of the error amplifier 17 corresponding to its difference, the base of the transistor 8 for constituting a constant- current source is biased. By this operation, with regard to the constant-current quantity of the constant-current source, a negative feedback control is executed as a circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an integrated circuit differential amplifier circuit, and particularly to an open collector output differential amplifier circuit.

(Prior Art) Conventionally, this type of differential amplifier circuit, for example, as shown in FIG. 3, and the base is the front stage circuit 3
A transistor 6 whose collector is connected to one output of the differential amplifier circuit and whose collector is connected to the output terminal 4 of the differential amplifier circuit, and whose base is connected to the other output of the pre-stage circuit 3 and whose collector is connected to the output terminal 5 of the differential amplifier circuit. The connected transistor 7, the transistor 8 whose collectors are connected to the common connection end (emitter) of the two transistors 6 and 7 forming a differential pair, and the constant voltage source 10 that biases the base of the transistor 8, It consists of a resistor 9 connected to the emitter of the transistor 8 and whose other end is grounded, a constant voltage source 13, and load resistors 1 and 12 connected between the constant voltage source 13 and the output terminals 4 and 5. There is.

(Problem to be solved by the invention) The differential gain Gv of the differential amplifier circuit shown in FIG.
The value of load resistor 11.12 is R5, and the resistance value of resistor 9 is RE
1, the voltage of the constant voltage source 10 is vl, and the forward voltage between the base and emitter of the transistor 8 is v6. and the electronic load is q1
If the Boltzmann constant is k and the absolute temperature is the king, then q Vl-VBE is obtained, which is inversely proportional to the resistance value R1 of the resistor 9. The absolute value of the resistance of an integrated circuit typically fluctuates by about ±20%, so if this circuit is integrated, the differential gain Gv will be -17.
% to +25%. Therefore, the gain Gv
For applications that require more stringent standards, conventional circuits may suffer from low manufacturing yields. To prevent this, it is possible to use the Zener IJ' knob or trimming the resistor, but this requires an extra process, and
It's going to be up.

In the conventional differential amplifier circuit mentioned above, the amount of current of the constant current source is directly affected by variations in the value of the resistance during semiconductor integrated circuit manufacturing, and as a result, the gain changes easily. It has the disadvantage that variations occur.

[Means for solving problems]

The differential amplifier circuit of the present invention compares the common-mode output voltage with a reference voltage, detects an error in the current amount of the constant current source from a predetermined value, and provides negative feedback so that the current amount becomes a predetermined value. It has a controlling error amplifier.

[Effect]

Therefore, the resistance values of the resistors that make up the constant current source vary! , : Even if the constant current amount deviates from the predetermined value (
error) is detected as a change in the common-mode output voltage of the differential amplifier circuit, and negative feedback control is performed according to the detection result, so the constant current amount is maintained at a predetermined value, resulting in gain fluctuation. do not have.

(Example) Next, an example of the present invention will be described with reference to the drawings.

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

In the differential amplifier circuit of this embodiment, the constant voltage source 10 is removed from the conventional circuit shown in FIG. The common-mode output voltage detection resistors 14 and 15 connected to each other at
A differential amplifier 17 whose output is connected to the base of the transistor 8 is added.

Here, the resistance value of the load resistors 11 and 12 is R1, the resistance values of the common-mode output voltage detection resistors 14 and 15 are both RA, and the voltage of the constant voltage source 13 is V. 0, and the voltage of the constant voltage source 16 for reference voltage is VR.

In addition, common mode output voltage detection resistor 14. ．． 15 resistance value R
is sufficiently larger than the resistance value R]- of the load resistor 11.12. Furthermore, it is assumed that the input impedance of the error amplifier 17 is sufficiently high.

Next, the operation of the embodiment will be explained. The voltage at the connection point A of the common-mode output voltage detection resistor 14.15 is the voltage at the connection point A of the two output terminals 4,
This is a voltage obtained by dividing the mutually opposite-phase output signals appearing in the output signals 5 and 5 into two, and is equal to the common-mode output voltage of the differential amplifier circuit. The potential at point A (common-mode output voltage) is compared with reference voltage VR, and the base of transistor 8 constituting the constant current source is biased by the output of error amplifier 17 according to the difference. Through this operation, negative feedback control is performed in terms of the circuit regarding the constant current amount of the constant current source. That is, since the common mode output voltage (potential at point A) changes depending on the constant current amount of the constant current source of the differential amplifier circuit, by comparing the common mode output voltage with the reference voltage VR, as a result, A deviation (error) in the amount of constant current from a predetermined value can be detected, and control is performed to correct this error. The collector voltage gain Gv of the transistor 6 when the offset voltage is O■ with the differential input OV is R1.RA. Since there is a relationship of RA>RL, q VCc-
VR...(1) becomes. The circuit of the first embodiment is determined by the electric voltage V.0 and the M quasi-voltage VR, and even if the resistance value within the integrated circuit changes, the differential gain Gv does not vary. There is no.

FIG. 2 is a circuit diagram showing a specific circuit of the error amplifier 17 and constant voltage source 16, which are similar to those shown in FIG.

The constant voltage source 16 includes a resistor 18 and a Zener diode 19, and the error amplifier 17 includes transistors 20 and 21 forming a differential pair, and a constant current source 22 that biases the differential pair.
and transistors 23 and 24 forming a current mirror circuit that receives the collector current of the transistor 21 as an input.
Common collector output transistor 25, 26 and resistor 2
It consists of 7.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

In the differential amplifier circuit of this embodiment, the constant □ current source 10 is removed from the conventional circuit shown in FIG. A diode 29 whose anode is connected to the cathode of the diode 28, a diode 30 whose anode is connected to the emitter of the transistor 7, a diode 31 whose anode is connected to the cathode of the diode 30, and a collector connected to the constant voltage source 13. A transistor 32 whose base is connected to the output terminal 4, a resistor 33 whose one end is connected to the emitter of the transistor 32 and whose other end is grounded, and whose collector is connected to the constant voltage source 13 and whose base is connected to the output terminal 5. A connected transistor 34, a resistor 35 having one end connected to the emitter of the transistor 34 and the other end grounded, a constant voltage source 16, and an error amplifier 17, each having one end connected to the emitter of the transistor 32, 34, In-phase output voltage detection resistors 36 and 37 whose other ends are connected to the non-inverting input of the error amplifier 17 are added.

The feature of the second embodiment is that the output terminals 4.5 of the differential amplifier circuit
A common-collector transistor 32.34 is interposed between the common-mode output voltage detection resistor 36.37,
Another point is that diodes 28 to 31 are connected to the emitters of transistors 6.7 forming a differential pair.

The configuration in which the common collector transistors 32 and 34 are present is effective in the following cases. For example, in the first embodiment (FIG. 1), when obtaining the common mode output voltage at point A because the input impedance of the error amplifier 17 is small,
The influence of the input impedance cannot be ignored and the common mode output voltage detection resistor 14.1 is used for adjustment.
There are times when it is necessary to reduce the resistance value R^ of 5.

At this time, between the resistance value R of the common mode output voltage detection resistor 14.15 and the resistance value R1 of the load resistor 11.12, R
There are cases where the relationship 1 does not hold, and in this case, the resistance 14.1! '+ is in parallel with the load resistances 11 and 12, and f4 is added as a load resistance, making it difficult to set an accurate gain.

However, as shown in FIG. 3, when the common-collector transistors 32 and 34 are installed, their input impedance is extremely large, so the load resistance 11°12 and the common-mode output voltage detection resistor 36,37 They are separated in terms of impedance, and the above-mentioned problems are solved.

Further, the circuit of this embodiment is also effective when it is desired to set the gain of the differential amplifier circuit low. That is, the error amplifier 17 controls the common mode output voltage to be vR0V. However, vR is constant voltage B [voltage of voltage line 16, ■BE is collector common transistor 3
This is the base-emitter forward voltage of 2 and 34. The differential gain Gv of the differential output stage at this time is equal to 10-qVCC'R'BE, which is about 1/3 of the gain of the first embodiment.

The number 3 appearing in the denominator of equation (2) means that two diodes (28, 29 or 30°31) are connected in series to each emitter of the transistors 6 and 7 forming a differential pair, and a differential amplification is performed. This is because one current path of the circuit has a configuration in which three diodes are actually interposed in series.The number of diodes connected to the emitter of the transistor 6.7 can be set arbitrarily. Yes, of course (2
) As is clear from the equation, even in the circuit of this embodiment, the differential gain Gv does not vary even if the resistance value of the integrated circuit varies.

As mentioned above, the second embodiment has the following problems: (1) In the first embodiment, since the human input impedance of the error amplifier 17 is small, it is necessary to reduce the resistance value 1 (8) of the resistors 14 and 15. If R>J does not hold or (2) differential gain of the output stage (
! This is effective when it is desired to reduce 7Gv.

〔Effect of the invention〕

As explained above, the present invention detects the variation in the constant current amount of the constant current source provided in the differential amplifier circuit as a change in the common mode output voltage, By performing negative feedback control, it is possible to prevent variations in the amount of constant current caused by variations in the resistance value, and as a result, it is effective to prevent variations in the differential gain of the differential amplifier@path.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of a first embodiment of the differential amplifier circuit of the present invention, FIG. 3 is a circuit diagram of a second embodiment of the differential amplifier circuit of the present invention, and FIG. 4 is a circuit diagram of a second embodiment of the differential amplifier circuit of the present invention. FIG. 2 is a circuit diagram of a conventional example. 1.2...Input terminal of differential amplifier circuit, 3...Bending circuit, 4.5...Output terminal of differential amplifier circuit, 6.7...Differential pair of differential amplifier circuit 8.9... Transistor and resistor constituting a constant current source of the differential amplifier circuit, 13... Constant voltage source, 11.12... Load resistance of the differential amplifier circuit, 14 .15
, 36.37... Resistor for common mode output voltage detection, 16... Constant voltage source for reference current path, 17... Error amplifier. Patent applicant: Hiki Electric Co., Ltd. Figure 1 Figure 2

Claims (1)

[Scope of Claims] In a differential amplifier circuit having a pair of transistors forming a differential pair and a constant current source connected to the transistors, a common mode output voltage and a reference voltage are compared, and the constant current source is 1. A differential amplifier circuit comprising an error amplifier that detects an error in the amount of current from a predetermined value and performs negative feedback control to control the amount of current so that the amount of current becomes the predetermined value.