JPH04150207A - Differential amplifier - Google Patents

Abstract

PURPOSE:To make an output voltage constant by providing a pinch resistor in which a resistance of an emitter resistor of the differential amplifier is adjusted through application of an external bias to the differential amplifier. CONSTITUTION:The differential amplifier consists of NPN transistors(TRs) 1-8, a pinch resistor 11, resistors 9, 10, 12-15, constant current sources 16, 17, and external terminals 18, 19. Then the resistor 11 whose resistance is variable by changing a region of a conduction channel through an external application bias is provided as an emitter resistor tying emitters of a couple of the TRs 1, 2 being components of the differential amplifier main body. Thus, since a current flowing to the differential amplifier main body and the load resistance are constant even when the adjustment is implemented to obtain a proper gain, the output voltage of the differential amplifier is made always constant.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a differential amplifier, and in particular to a differential amplifier equipped with a resistor whose emitter resistance value can be adjusted by applying an external bias. Regarding the amplifier.

[Conventional technology]

In conventional differential amplifiers, there is nothing in particular to adjust the resistance value by applying an external bias, and the emitter resistance is a fixed resistance. For example, if you want to adjust the gain of the differential amplifier as shown in FIG. 4, transistors 37, 38 . A constant current circuit formed by resistors 43 and 44 is connected to an external terminal 47.
By applying a bias from the external terminal 47, the current in the differential amplifier body is changed, g, (mutual fundance) is changed, and adjustment is performed to obtain an appropriate gain.

The differential amplifier itself has resistors 39, 40, 41°42 and n
pn) transistors 31, 32, 33, 34 and constant current 4
5.46, and also includes a constant current circuit (described later).

[Problem to be solved by the invention]

In the conventional differential amplifier described above, in order to obtain an appropriate gain, a constant current circuit is connected to the external terminal 47, and a bias is applied from the external terminal to change the current of the differential amplifier. Since the current of the differential amplifier must be controlled and the gain adjusted, there is a problem that the current of the differential amplifier is not constant and the output voltage is not always constant.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a differential amplifier whose output voltage is constant.

[Means to solve the problem]

The configuration of the present invention is characterized in that the resistor, which is variable by changing the area of the conduction channel by an externally applied bias, is provided as an emitter resistor that connects the emitters of a pair of transistors that constitute the differential amplifier main body. shall be.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing a differential amplifier according to an embodiment of the present invention. In FIG. 1, this embodiment includes NPN) transistors 1 to 8, a pinch resistor 11, and resistors 9, 10, and 12 to 8.
15, constant current sources 16 and 17, and external terminals 18 and 19.

This embodiment differs from FIG. 4 in that a pinch resistor 11 and an external terminal 18 are added.

FIG. 2 is a cross-sectional view of the structure of a pinch resistor whose resistance value can be adjusted by applying an external bias to the resistance value of the emitter resistor of the differential amplifier shown in FIG.

FIG. 3 is a plan view of the pinch resistance portion. Figures 2 and 3
In the figure, an oxide film 22, a high concentration N-type diffusion Ji 23, a P" diffusion layer 24, a depletion layer 25, an Epi (epitaxial) N- layer 26, a buried layer 27, and a Sub straight 28. , contact 29 , and external terminal 30
is shown. In FIG. 2, the high concentration N-type diffusion layer 2
By applying a bias from the outside to 3, the depletion layer 25 is widened, and the resistance value of the pinch resistor 11 shown in FIG. 1 can be adjusted.

〔Effect of the invention〕

As explained above, the present invention has a pinch resistor that can adjust the resistance value of the emitter resistor of the differential amplifier by applying an external bias, so that even if the gain is adjusted to an appropriate level, the difference Since the current flowing through the main body of the differential amplifier and the load resistance are constant, the output voltage of the differential amplifier can be kept constant at all times.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a differential amplifier according to an embodiment of the present invention, and FIG.
3 is a cross-sectional view showing the structure of the pinch resistor shown in FIG. 1, FIG. 3 is a plan view showing the shape of the pinch resistor shown in FIG. 2, and FIG. 4 is a circuit diagram of a conventional differential amplifier. 1 to 8 are NPN) transistors, 11 is a pinch resistor, 9
, 10.12-15.39-44 are resistances, 16.17,
46.47 is a constant current, 18.19 is an external terminal, 22 is an oxide film, 23 is a high concentration N type diffusion layer, 24 is a P3 diffusion layer, 2
5 is a depletion layer, 26 is an EpfN- layer, 27 is a buried layer, 28
is a Sub straight, 29 is a direct contact, 30.47 is an external terminal, and 31 to 38 are NPN) transistors.

Claims (1)

[Claims] A differential amplifier characterized in that a resistor that is variable by changing the area of a conduction channel by an externally applied bias is provided as an emitter resistor that connects the emitters of a pair of transistors constituting a main body of the differential amplifier.