JPS63234705A - Differential amplifier - Google Patents

Abstract

PURPOSE:To obtain an operable differential amplifier even the threshold voltage of an FET is scattered by providing third and fourth FETs, which have respectively a serial resistance at a source side and in which a resistance edge is connected to a gate, between respective drains of first and second FETs and a first power source. CONSTITUTION:To the source side of FETs 3 and 4 for a load, serial resistances 7 and 8 are respectively connected and for respective gates, a bias is added from these resistance edges. When a current to flow at an FET is IDSS and the resistance of the serial connection to a source is RS, a gate bias is a potential lower than the potential of a source only by IDSSXRS. Consequently, the operable threshold voltage of the FET can be obtained from -IDSSXRS up to zero. According to the constitution, even when variance exists at the threshold voltage of the FET, the differential amplifier is constituted and can be sufficiently operated with the wide scope.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a differential amplifier using field effect transistors.

Conventional technology In semiconductor devices based on compound semiconductors, especially gallium arsenide (GaAs), field-effect transistors are the most notable circuit element, and the sysget-key junction gate is used as a field-effect transistor (hereinafter abbreviated as MESFICT). ) are used in differential amplifiers. Conventionally, a differential amplifier using MKSFET has been known to have a circuit configuration as shown in FIG. Second 1llcsF
For ET1.2, load drawing cylinder 3. 4th MKSFE
T3 and T4 are connected as a resistance element by connecting their sources and gates in common. In addition,
The differential pair MKSFICTl, the sixth MKSFKTs coupled to the common source of 2 and the resistor 6 are current source circuit components.

Problems to be Solved by the Invention According to the conventional circuit configuration shown in Figure 3, in order for current to flow through the MKSFET, the MKSFET must have a threshold voltage near zero potential due to the circuit configuration. No current flows. Another drawback is that the equivalent resistance value of the MKSFET used as a load becomes small. Threshold voltage varies widely due to process effects,
MESFICT whose threshold voltage is near zero potential within the wafer
It is difficult to create this over the entire surface. For this reason,
In the conventional circuit configuration, it was not possible to form MIC8FETs with the same amplification function over the entire surface of the wafer, and there was a problem that the characteristics varied when an integrated circuit was constructed.

The present invention provides a circuit configuration that can solve the above-mentioned problems.

Means for Solving the Problems The present invention provides the first . The third field-effect transistor has a series resistor on the source side between each drain of the second field-effect transistor and the first power supply, and the resistor end is connected to the gate. This is a differential amplifier equipped with a fourth field effect transistor.

Action.

According to the present invention, field effect transistors forming a differential amplifier can operate over a wide range of threshold voltages.

Embodiment A circuit configuration of an embodiment of the present invention is shown in FIG. In this embodiment configuration, on the source side of the load MIC5FIET3.4,
Series resistors 7 and 8 are connected to each gate, and a bias is applied to each gate from the terminals of these resistors. Assuming that the current flowing through the MKSFET is 105g and the resistor connected in series on the source side is R3, the gate bias becomes a potential lower than the potential of the source source by I, 88·Rs. Therefore, the operable threshold voltage of the MIESFET can range from - to R8/R8 to 0.

For example, if I, . . . = 1 nm and R5 = 600Ω, the operable threshold voltage will be in the range of −0.6 to Ov. In FIG. 2, the characteristics of the circuit according to the embodiment of the present invention are shown by solid lines, and the characteristics of the conventional example are shown by broken lines. The horizontal axis shows the threshold voltage, and the vertical axis shows the amplification degree. As shown in the figure, the effects of the present invention can be confirmed.

In the embodiment, the amplification degree is set to be QdB or more, but a digital differential amplifier with an increase of $1110 dB may be used.

Effects of the Invention According to the present invention, even if the threshold voltages of MIESFETs vary, a differential amplifier can be configured and operate satisfactorily over a wide range. Therefore, the MKSFET has the effect of providing a differential amplifier that can operate with high yield even if the threshold voltage varies due to the diffusion process.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a characteristic diagram of the embodiment, and FIG. 3 is a circuit diagram of a conventional structure. 1~5...MESFICT, e~8...
···resistance. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
figure

Claims (1)

[Claims] A third field-effect transistor having a series resistance on the source side is connected between the drain of the first field-effect transistor and the second field-effect transistor having the differential pair configuration and the first power supply, and a third field-effect transistor having a resistor end connected to the gate. A differential amplifier equipped with 4 field effect transistors.