JP2545374B2 - Differential amplifier circuit having constant current source circuit - Google Patents

Description

The present invention relates to a constant current source circuit, and more particularly to a constant current source having a predetermined temperature coefficient utilizing temperature characteristics of threshold voltage of P-channel MOS transistors and N-channel MOS transistors. A differential amplifier circuit having a constant current circuit that constitutes a circuit unit and obtains a current output having a desired temperature characteristic is described.

[Industrial applications]

The present invention relates to a differential amplifier circuit having a constant current source circuit. The circuit according to the present invention is used, for example, in an emitter coupled logic circuit for computer circuits.

[Prior art and problems to be solved by the invention]

For example, in an ECL (emitter coupled logic) circuit, a constant current source circuit is used. The current of this constant current source circuit is normally considerably stabilized against fluctuations in the power supply voltage, but it is stable against changes in temperature. Stability may not always be sufficient. In particular, when a large number of ECL circuits are connected in multiple stages, the voltage of the logic level of the output signal fluctuates even if the current of the constant current circuit slightly fluctuates, and the voltage margin decreases.

Conventionally, a constant current circuit used in an ECL circuit or the like compensates the temperature characteristic of the output current by utilizing the temperature characteristic of the forward voltage of the diode or the voltage between the base and emitter of the bipolar transistor. Alternatively, in a constant current circuit using a MOS transistor, the output current is stabilized by using a negative feedback circuit.

However, these conventional constant current source circuits have a problem that it is extremely difficult to set the temperature coefficient of the output current to a desired value.

In view of the problems in the above-mentioned conventional type, an object of the present invention is to determine the temperature characteristics of the output current based on the concept of combining the outputs of a plurality of constant current source circuit sections having different temperature coefficients in a constant current source circuit. The purpose is to be able to set the desired characteristics.

[Means for solving problems]

According to the present invention, there is provided a differential amplifier circuit having a differential circuit including a pair of differential transistors whose sources are commonly connected, and a constant current circuit connected to a common source side of the differential circuit, The constant current source circuit includes a first P-channel MOS transistor and a first resistor connected in series between a high power supply and a low power supply, and a first P-channel MOS transistor connected in series between a high power supply and a low power supply. Two resistors and a second P-channel MOS transistor, the gate of the first P-channel MOS transistor is connected to the connection point of the second resistor and the second P-channel MOS transistor, The gate of the P-channel MOS transistor is connected to the connection point of the first P-channel MOS transistor and the first resistor, and the constant current source circuit has a current mirror circuit having third and fourth MOS transistors. However, the third MOS transistor is provided between the second P-channel MOS transistor and the low power supply, and the fourth MOS transistor is provided between the common source and the low power supply. A differential amplifier circuit having a constant current source circuit, wherein the output current flowing through the source circuit increases with an increase in temperature, and the constant current source circuit lowers the output voltage of the differential circuit. .

〔Example〕

The principle of a differential amplifier circuit having a constant current source circuit according to the present invention will be described with reference to FIG. The circuit in FIG.
Differential circuit A ₁ such as current switch or differential amplifier, common emitter or common source of differential circuit A ₁ and power supply V _SS
A parallel circuit of MOS transistors Q ₁ and Q ₂ inserted between them, and a constant current source circuit section CS having a predetermined temperature coefficient connected to the gate of the transistor Q ₁ are provided.

In the circuit of FIG. ₁ , the drain current IS of the transistor Q ₁ has a predetermined temperature coefficient as shown in FIG. 2 which is controlled by the constant current source circuit section CS having a positive temperature coefficient.

FIG. 3 specifically shows the configuration of a constant current source circuit according to one embodiment of the present invention. The circuit in the figure shows differential transistors Q ₃ and Q ₄ with their sources connected in common and a load resistor R ₁ and
It has a differential circuit A ₁ having R ₂ . Transistor Q ₃ and
An N-channel MOS transistor Q ₈ , P-channel MOS transistors Q ₉ and Q ₁₉ and a resistor, which form a constant current source circuit section CS having a predetermined temperature coefficient, connected to a common source of Q _4.
It is provided with R ₅ and R ₆ and an N-channel MOS transistor Q ₇ which constitutes a current combining circuit. In the circuit of FIG. 3, a high potential power supply V _CC and a low potential power supply V _SS are used.

In the circuit of FIG. 3, the threshold characteristics of the P-channel MOS transistors Q ₉ and Q ₁₀ of the constant current source circuit CS are as shown in FIG.
The drain current I _D increases with respect to V ₆ . That is, the threshold voltage of the gate tends to decrease. Therefore, as the temperature rises, the current flowing through the resistor R ₅ increases, and the current flowing through the transistor Q ₈ also increases. Since the transistor Q ₈ and the transistor Q ₇ form a current mirror circuit,
The current IS flowing through the transistor Q ₇ also increases as the temperature rises. Therefore, the constant current circuit section CS acts in a direction of lowering the potentials of the output voltages Vo ₁ and Vo ₂ of the differential circuit according to the temperature rise.

In the circuit of FIG. 3, since the transistors Q ₉ and Q ₁₀ of the constant current source circuit section CS ₁ and the negative feedback circuit are configured, the output current IS is stabilized even when the power supply voltage V _CC changes. Has been done.

〔The invention's effect〕

As described above, according to the present invention, since the current output is obtained by the constant current source circuit unit having a predetermined temperature coefficient, a desired temperature coefficient can be obtained according to the characteristics of the circuit such as the ECL circuit and the usage conditions. A differential amplifier circuit having a constant current source circuit that outputs the output current can be realized.

[Brief description of drawings]

FIG. 1 is a block circuit diagram for explaining the principle of a differential amplifier circuit having a constant current source circuit according to the present invention, FIG. 2 is a graph showing characteristics of the circuit of FIG. 1, and FIG. Of 1
FIG. 4 is an electric circuit diagram showing a constant current source circuit according to the embodiment, and FIG. 4 is a characteristic diagram for explaining the operation of the circuit of FIG. A ₁ : a differential circuit, CS: a constant current source circuit section having a predetermined temperature coefficient, Q ₁ , Q ₂ , ..., Q ₁₀ : MOS transistors, R ₁ , R ₂ , ..., R ₆ : resistors.

Claims (1)

(57) [Claims] 1. A differential amplifier circuit having a differential circuit composed of a pair of differential transistors whose sources are commonly connected, and a constant current source circuit connected to a common source side of the differential circuit. The constant current source circuit includes a first P-channel MOS transistor and a first resistor connected in series between a high power source and a low power source, and a serial connection between a high power source and a low power source in series. A second resistor and a second P-channel MOS transistor, wherein a gate of the first P-channel MOS transistor is connected to a connection point of the second resistor and the second P-channel MOS transistor; Of the P-channel MOS transistor is connected to the connection point of the first P-channel MOS transistor and the first resistor, and the constant current source circuit has a current mirror circuit having third and fourth MOS transistors. Then The third MOS transistor is provided between the second P-channel MOS transistor and the low power supply, and the fourth MOS transistor is provided between the common source and the low power supply, whereby the constant current source circuit is provided. A differential amplifier circuit having a constant current source circuit, wherein the output current flowing through the constant current source circuit increases as the temperature rises, and the constant current source circuit lowers the output voltage of the differential circuit.