Differential amplifier with temperature compensation

Abstract

This differential amplifier with temperature compensation includes: a temperature compensation circuit having a positive temperature coefficient; a first transistor; and a third transistor and a second transistor for amplifying a voltage difference applied to each first terminal. A power source is electrically connected to a second terminal of each of the second transistor and the third transistor. A third terminal of the second transistor, a third terminal of the third transistor, and a second terminal of the first transistor are connected. One end of the temperature compensation circuit is connected to the power source, and the other end thereof is connected to the third terminal of the second transistor, the third terminal of the third transistor, and the second terminal of the first transistor.

Description

Temperature compensated differential amplifier

[0001] This application claims priority to Japanese Patent Application No. 2024-083484, filed May 22, 2024, the contents of which are incorporated herein by reference.

[0002] A differential amplifier circuit is known that uses two transistors or two FETs (field-effect transistors) with identical characteristics to amplify the difference between two input signals by a constant coefficient (differential gain). A differential amplifier circuit with a tail constant current source is commonly used as a high-frequency signal amplifier. For example, Patent Document 1 discloses a configuration in which a differential amplifier circuit with a tail constant current source uses a temperature compensation circuit to compensate for gain fluctuations due to temperature fluctuations. The temperature detection functional block required to compensate for gain fluctuations due to temperature fluctuations is composed of, for example, a bandgap reference circuit, a temperature-current conversion circuit including an operational amplifier, and the like. Such a temperature compensation circuit requires high output current accuracy.

[0003] U.S. Patent No. 6,583,667

[0004] However, in the configuration described in Patent Document 1, the bias current is varied not only to perform variable gain control but also to compensate for gain fluctuations due to temperature fluctuations. Therefore, even if the same gain is maintained, if the temperature fluctuates, the DC current consumption of the differential amplifier circuit also fluctuates, changing the amount of heat generated by all the components that make up the circuit, and this may result in a longer time until the gain stabilizes when the temperature changes.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a temperature-compensated differential amplifier that can reduce the time it takes for the gain to converge and stabilize when the temperature changes.

[0006] In order to achieve the above object, a temperature-compensated differential amplifier according to a first aspect of the present disclosure comprises a temperature compensation circuit having a positive temperature coefficient, a first transistor, and second and third transistors that amplify the voltage difference applied to each first terminal, wherein a power supply is electrically connected to the second terminals of the second transistor and the third transistor, and the third terminal of the second transistor, the third terminal of the third transistor, and the second terminal of the first transistor are connected, and the temperature compensation circuit has one end connected to the power supply and the other end connected to the third terminal of the second transistor, the third terminal of the third transistor, and the second terminal of the first transistor.

[0007] A temperature-compensated differential amplifier according to a second aspect of the present disclosure is the same as that of the first aspect, and includes a first resistor, a second resistor, a first load, and a second load, wherein the second transistor has a second terminal connected to the power supply via the first load and outputs a negative output voltage from the second terminal, a first terminal connected to one end of the first resistor and receives a positive input signal at the first terminal, and a first predetermined voltage is supplied to the other terminal of the first resistor, the third transistor has a second terminal connected to the power supply via the second load and outputs a positive output voltage from the second terminal, a first terminal connected to one end of the second resistor and receives a negative input signal at the first terminal, and the second resistor receives the first predetermined voltage at the other terminal, and the first transistor has a third terminal grounded and a control voltage input to the first terminal.

[0008] A temperature-compensated differential amplifier according to a third aspect of the present disclosure is the same as that of the second aspect, wherein the temperature compensation circuit includes a third resistor having a positive temperature coefficient, one end of the third resistor being connected to the power supply and the other end being connected to the second terminal of the first transistor.

[0009] A temperature-compensated differential amplifier according to a fourth aspect of the present disclosure is the same as that of the second aspect, except that the temperature compensation circuit includes a third resistor having a positive temperature coefficient and a fourth resistor having a positive temperature coefficient, one end of the fourth resistor being connected to the power supply and the other end being connected to one end of the third resistor, and the other end of the third resistor R3 being connected to the second terminal of the first transistor.

[0010] A temperature-compensated differential amplifier according to a fifth aspect of the present disclosure is the same as that of the second aspect, wherein the temperature compensation circuit includes a fourth transistor having an on-resistance with a positive temperature coefficient, the fourth transistor having a second terminal connected to the power supply and a third terminal connected to the second terminal of the first transistor, and a first terminal of the fourth transistor is supplied with a second predetermined voltage that maximizes the effect of suppressing fluctuations in the transconductance of the second transistor and the third transistor.

[0011] A temperature-compensated differential amplifier according to a sixth aspect of the present disclosure is the same as that of the second aspect, wherein the temperature compensation circuit includes a fourth transistor whose on-resistance has a positive temperature coefficient and a third resistor having a positive temperature coefficient, the fourth transistor has a second terminal connected to the power supply and a third terminal connected to one end of the third resistor, the third resistor has the other end connected to the second terminal of the first transistor, and a second predetermined voltage is supplied to the first terminal of the fourth transistor, which voltage maximizes the effect of suppressing fluctuations in the transconductance of the second transistor and the third transistor.

[0012] A temperature-compensated differential amplifier according to a seventh aspect of the present disclosure is the same as that of the second aspect, wherein the temperature compensation circuit includes a fourth transistor whose on-resistance has a positive temperature coefficient, a third resistor having a positive temperature coefficient, and a fourth resistor having a positive temperature coefficient, one end of the fourth resistor connected to the power supply and the other end connected to a second terminal of the fourth transistor, a third terminal of the fourth transistor connected to one end of the third resistor, and the other end of the third resistor connected to the second terminal of the first transistor, and a second predetermined voltage that maximizes the effect of suppressing fluctuations in the transconductance of the second transistor and the third transistor is supplied to the first terminal of the fourth transistor.

[0013] According to the present disclosure, it is possible to reduce the time it takes for the gain to converge and stabilize when the temperature changes.

[0014] 1 is a diagram illustrating a configuration example of a temperature-compensated differential amplifier according to an embodiment; FIG. 2 is a diagram illustrating a configuration example of a temperature compensation circuit according to an embodiment; FIG. 3 is a diagram illustrating a configuration example of a temperature compensation circuit according to an embodiment;１ , I ２ , I ３ , I ４ 10 is an image diagram showing an example of change in

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 is a diagram illustrating an example configuration of a temperature-compensated differential amplifier according to this embodiment. As shown in FIG. 1 , the temperature-compensated differential amplifier 1 according to this embodiment includes, for example, a first transistor M1, a second transistor M2, a third transistor M3, a first resistor R1, a second resistor R2, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a first inductor L1 (first load), a second inductor L2 (second load), and a temperature compensation circuit A1. In this embodiment, the gate G of the transistor is referred to as a first terminal, the drain D as a second terminal, and the source S as a third terminal.

[0016] The temperature compensation circuit A1 has one end connected to the power supply VDD and the other end connected to the drain D of the first transistor M1, the source S of the second transistor M2, and the source S of the third transistor M3. The first inductor L1 has one end connected to the power supply VDD and the other end connected to one end of the third capacitor C3 and the drain D of the second transistor M2. Thus, the drain D of the second transistor M2 is electrically connected to the power supply VDD via the first inductor L1. The third capacitor C3 outputs a negative output voltage Voutn from the other end. The second transistor M2 has a gate G connected to one end of the first capacitor C1 and one end of the first resistor R1. The first capacitor C1 receives a positive input signal Vinp at the other end. The first resistor R1 receives a first predetermined voltage Vb at the other end. The first predetermined voltage Vb is a predetermined fixed voltage that provides a desired gain in the second transistor M2 and the third transistor M3. One end of the second inductor L2 is connected to the power supply VDD, and the other end is connected to one end of the fourth capacitor C4 and the drain D of the third transistor M3. In this way, the drain D of the third transistor M3 is electrically connected to the power supply VDD via the second inductor L2. The fourth capacitor C4 outputs a positive output voltage Voutp from the other end. The third transistor M3 has a gate G connected to one end of the second capacitor C2 and one end of the second resistor R2. The second capacitor C2 receives a negative input signal Vinn at its other end. The second resistor R2 receives a first predetermined voltage Vb at its other end. The first transistor M1 has a source S grounded, and a control voltage Vtail input to its gate G.

[0017] The current flowing through the first transistor M1 is I １ , the current flowing through the second transistor M2 is I ２ , the current flowing through the third transistor M3 is I ３ , the current flowing through the temperature compensation circuit A1 is I ４ Let's say.

[0018] The circuit configuration of Figure 1 is a differential amplifier circuit including a pair of differential transistors, a second transistor M2 and a third transistor M3, a pair of a first inductor L1 and a second inductor L2, and a first transistor M1 for a tail constant current source, in which a temperature compensation circuit A1 is connected between the drain D of the first transistor M1 and a power supply VDD.

[0019] The second transistor M2 and the third transistor M3 are, for example, N-channel MOS (metal-oxide semiconductor) field-effect transistors (FETs). The second transistor M2 and the third transistor M3 preferably have the same characteristics. When input signals of opposite polarities are applied to their gates G (first terminals), the second transistor M2 and the third transistor M3 function as a differential amplifier circuit that obtains output voltages of opposite polarities from their drains D (second terminals).

[0020] The first inductor L1 and the second inductor L2 are load inductors, and it is preferable that the inductance values ​​of the first inductor L1 and the second inductor L2 are the same.

[0021] The third capacitor C3 and the fourth capacitor C4 are used to cut DC components. In this way, the output of the temperature compensated differential amplifier 1 is output to a connected circuit or the like via the third capacitor C3 and the fourth capacitor C4.

[0022] The first capacitor C1 and the second capacitor C2 are used to cut DC components. A high-frequency positive input signal Vinp, for example, is input to the gate G of the second transistor M2 via the first capacitor C1. A high-frequency negative input signal Vinn, for example, is input to the gate G of the third transistor M3 via the second capacitor C2. The first resistor R1 and the second resistor R2 are used to supply a first predetermined voltage Vb, which is sufficient to obtain a desired gain, to the gate G of the second transistor M2 and the third transistor M3, respectively.

[0023] A control voltage Vtail is controlled by, for example, a current mirror circuit and input to the gate G of the first transistor M1 so that a direct current necessary to obtain a desired gain flows.

[0024] The temperature compensation circuit A1 is an element or circuit with a positive temperature coefficient. An example configuration of the temperature compensation circuit A1 will be described later. This temperature compensation circuit A1 has a function of bypassing a portion of the DC current generated by the first transistor M1 of the tail current source, preventing it from flowing to the pair of the second transistor M2 and the third transistor M3. Therefore, when the ambient temperature rises, the resistance of the temperature compensation circuit A1 increases, and the DC current flowing through the temperature compensation circuit A1 decreases. When the ambient temperature drops, the resistance of the temperature compensation circuit A1 decreases, and the DC current flowing through the temperature compensation circuit A1 increases. As a result, the DC current flowing through the second transistor M2 and the third transistor M3 increases when the temperature rises and decreases when the temperature drops. As a result, the configuration of FIG. 1 can suppress fluctuations in the transconductance (gm) (transistor mutual conductance) of the differential second transistor M2 and the third transistor M3 due to temperature fluctuations. The transconductance is the ratio of the change in drain current to a slight change in voltage between the gate G and the source S. As a result, according to this embodiment, gain stabilization can be achieved without requiring a complex and large-scale functional block as described in Cited Document 1.

[0025] In this embodiment, Vtail is adjusted so that the DC current value flowing through the first transistor M1 for the tail constant current source does not change with temperature fluctuations. Therefore, according to this embodiment, even if the temperature fluctuates as long as the same gain is maintained, the DC current consumption of the differential amplifier circuit does not change accordingly, and the amount of heat generated by the components (especially the transistors) that make up the circuit does not change. As a result, according to this embodiment, it takes a short time for the gain to converge and stabilize when the temperature changes.

[0026] 1 shows an example of a differential circuit for use with high frequencies, but the frequency band in use is not limited to this. Depending on the frequency band in use, the first inductor L1 and the second inductor L2 may be resistors.

[0027] 1 shows an example in which the first transistor M1 to the third transistor M3 are N-channel FETs, but the first transistor M1 to the third transistor M3 may also be P-channel FETs. However, if P-channel transistors are used for the first transistor M1 to the third transistor M3, a tail current source is provided between the common source of the second transistor M2 and the third transistor M3 and the power supply VDD, and load resistors are provided between the drains of the second transistor M2 and the third transistor M3 and the ground GND. In each of these configurations, the supplied voltage, etc., need only be suited to the transistors used.

[0028] Furthermore, the temperature compensated differential amplifier may not have the first capacitor C1 to the fourth capacitor C4 in FIG. 1 depending on the application, control signal, etc.

[0029] (Configuration Example of Temperature Compensation Circuit) Next, a configuration example of a temperature compensation circuit will be described with reference to Figures 2 and 3. Figures 2 and 3 are diagrams showing a configuration example of a temperature compensation circuit according to this embodiment. Note that Figures 2 and 3 show only the first transistor M1 connected to the temperature compensation circuit A1, and omit other components.

[0030] In the example of reference symbol g10 in FIG. 2 , the temperature compensation circuit A1 includes a third resistor R3 with a positive temperature coefficient. The third resistor R3 is, for example, a linear positive temperature coefficient resistor. The value of the third resistor R3 is set, for example, by simulation or actual measurement, depending on the differential amplifier circuit to be used. In this configuration, one end of the third resistor R3 is connected to the power supply VDD, and the other end of the third resistor R3 is connected to the drain D of the first transistor M1, etc.

[0031] In the example of reference symbol g20 in FIG. 2 , the temperature compensation circuit A1 includes two resistors, a third resistor R3 and a fourth resistor R4, each having a positive temperature coefficient. The third resistor R3 and the fourth resistor R4 are, for example, linear positive temperature coefficient resistors. The values ​​of the third resistor R3 and the fourth resistor R4 are set, for example, by simulation or actual measurement, depending on the differential amplifier circuit to be applied. In this configuration, one end of the fourth resistor R4 is connected to the power supply VDD, the other end of the fourth resistor R4 is connected to one end of the third resistor R3, and the other end of the third resistor R3 is connected to the drain D of the first transistor M1, etc.

[0032] The configuration of symbol g20 uses two resistor elements with different temperature coefficients connected in series, which allows the resistance value and temperature coefficient to be set independently. With this configuration, for example, it is possible to use an element with a zero coefficient for temperature as the fourth resistor R4.

[0033] 3, the temperature compensation circuit A1 includes a fourth transistor M4, which is a MOS FET whose on-resistance has a positive temperature coefficient. In this configuration, the drain D of the fourth transistor M4 is connected to the power supply VDD, and the source S of the fourth transistor M4 is connected to the drain D of the first transistor M1, etc. In addition, an optimal second predetermined voltage Vc is supplied to the gate of the fourth transistor M4, which maximizes the effect of suppressing fluctuations in the transconductance of the second and third differential transistors M2 and M3.

[0034] According to the configuration indicated by the symbol g30, by using the same type of transistors as the differential pair of the second transistor M2 and the third transistor M3 instead of resistor elements, fluctuations in the same direction can be expected not only with respect to temperature but also with respect to process fluctuations. Therefore, the temperature characteristics with respect to DC current shown in FIG. 4 can be expected to have a correction effect on the process fluctuation characteristics with respect to DC current (for example, from a fast process to a slow process).

[0035] 3 , the temperature compensation circuit A1 includes a fourth transistor M4, which is a MOS FET whose on-resistance has a positive temperature coefficient, and a third resistor R3, which also has a positive temperature coefficient. In this configuration, the drain D of the fourth transistor M4 is connected to the power supply VDD, the source S of the fourth transistor M4 is connected to one end of the third resistor R3, and the other end of the third resistor R3 is connected to the drain D of the first transistor M1, etc. In addition, an optimal second predetermined voltage Vc is supplied to the gate of the fourth transistor M4, which maximizes the effect of suppressing fluctuations in the transconductance of the second and third differential transistors M2 and M3.

[0036] According to the configuration of reference symbol g40, the linearity of the drain current of the transistor with respect to the control voltage Vc can be improved by providing a resistive element on the source side of the transistor. As a result, the configuration of reference symbol g40 improves the ease of current control using the control voltage Vc.

[0037] 3 , the temperature compensation circuit A1 includes a fourth transistor M4, which is a MOS FET whose on-resistance has a positive temperature coefficient, and two resistors, a third resistor R3 and a fourth resistor R4, each having a positive temperature coefficient. In this configuration, one end of the fourth resistor R4 is connected to the power supply VDD, the other end of the fourth resistor R4 is connected to the drain D of the fourth transistor M4, the source S of the fourth transistor M4 is connected to one end of the third resistor R3, and the other end of the third resistor R3 is connected to the drain D of the first transistor M1, etc. In addition, an optimal second predetermined voltage Vc is supplied to the gate of the fourth transistor M4, which maximizes the effect of suppressing fluctuations in the transconductance of the second and third differential transistors M2 and M3.

[0038] The configuration of reference symbol g50 adds the design parameter of the fourth resistor R4, facilitating optimal design of the DC current to be passed through the temperature compensation circuit that operates on the potential difference between the power supply VDD and the tail current source. The configuration of reference symbol g50 makes it possible to select, for example, the size of the fourth transistor M4 and the resistance value of the fourth resistor R4 independently.

[0039] (Change in DC current with respect to temperature change) Figure 4 shows the change in DC current I with respect to the temperature change around the circuit.１ , I ２ , I ３ , I ４ 10 is an image diagram showing an example of change in

[0040] In Fig. 4, the horizontal axis represents temperature (degrees) and the vertical axis represents DC current (mA). Note that the temperature on the horizontal axis is lower on the left and higher on the right. The line g101 represents the DC current I １ The line g102 shows an example of the change in the DC current I flowing through the second transistor M2. ２ and the DC current I flowing through the third transistor M3 ３ The line g103 shows an example of the change in the sum of the DC current I flowing through the temperature compensation circuit A1. ４ This is an example of the change in response to temperature change.

[0041] As shown by the line g101, even if the ambient temperature changes, the DC current I flowing through the first transistor M1 １ The control voltage Vtail supplied to the gate G of the first transistor M1 is adjusted so that the DC current I ４ As a result, as shown by the line g102, the DC current I flowing through the second transistor M2 and the third transistor M3 decreases as the ambient temperature increases. ２ +I ３ Generally, transconductance has a negative coefficient with respect to temperature, but a positive coefficient with respect to DC current, so the fluctuation of the transconductance of the second transistor M2 and the third transistor M3 with respect to temperature is suppressed.

[0042] As described above, according to this embodiment, the circuit scale can be made smaller than in the prior art, thereby stabilizing the gain. Furthermore, according to this embodiment, even if the temperature fluctuates as long as the same gain is maintained, the DC current consumption of the differential amplifier circuit does not change and the amount of heat generated by all the components that make up the circuit does not change accordingly, so it takes a short time for the gain to converge and stabilize when the temperature changes.

[0043] The temperature-compensated differential amplifier is suitable for use as, for example, a high-frequency signal amplifier. The frequency band in which the temperature-compensated differential amplifier is used is not limited to high frequencies, and it may also be low frequencies, the audio band, etc. Furthermore, some or all of the circuits shown in Figures 1 to 3 may be integrated circuits.

[0044] The above describes the form for implementing the present disclosure using embodiments, but the present disclosure is not limited to these embodiments in any way, and various modifications and substitutions can be made within the scope that does not deviate from the gist of the present disclosure.

[0045] M1...first transistor, M2...second transistor, M3...third transistor, R1...first resistor, R2...second resistor, C1...first capacitor, C2...second capacitor, C3...third capacitor, C4...fourth capacitor, L1...first inductor, L2...second inductor, A1...temperature compensation circuit, R3...third resistor, R4...fourth resistor, M4...fourth transistor

Claims

1. A temperature compensated differential amplifier comprising: a temperature compensation circuit having a positive temperature coefficient; a first transistor; and second and third transistors that amplify the voltage difference applied to their first terminals, wherein a power supply is electrically connected to the second terminals of the second and third transistors; the third terminal of the second transistor, the third terminal of the third transistor, and the second terminal of the first transistor are connected together; and the temperature compensation circuit has one end connected to the power supply and the other end connected to the third terminal of the second transistor, the third terminal of the third transistor, and the second terminal of the first transistor.

2. The temperature compensated differential amplifier according to claim 1, comprising a first resistor, a second resistor, a first load, and a second load; wherein the second transistor has a second terminal connected to the power supply via the first load and outputs a negative output voltage from the second terminal, a first terminal connected to one end of the first resistor and receives a positive input signal to the first terminal, and a first predetermined voltage is supplied to the other end of the first resistor; the third transistor has a second terminal connected to the power supply via the second load and outputs a positive output voltage from the second terminal, a first terminal connected to one end of the second resistor and receives a negative input signal to the first terminal, and the second resistor receives the first predetermined voltage to the other end; and the first transistor has a third terminal grounded and receives a control voltage to the first terminal.

3. The temperature-compensated differential amplifier according to claim 2, wherein the temperature compensation circuit comprises a third resistor having a positive temperature coefficient, one end of the third resistor being connected to the power supply and the other end being connected to the second terminal of the first transistor.

4. The temperature compensated differential amplifier according to claim 2, wherein the temperature compensation circuit comprises a third resistor having a positive temperature coefficient and a fourth resistor having a positive temperature coefficient, one end of the fourth resistor being connected to the power supply and the other end being connected to one end of the third resistor, and the other end of the third resistor R3 being connected to the second terminal of the first transistor.

5. The temperature-compensated differential amplifier according to claim 2, wherein the temperature compensation circuit comprises a fourth transistor whose on-resistance has a positive temperature coefficient, the fourth transistor has a second terminal connected to the power supply and a third terminal connected to the second terminal of the first transistor, and the first terminal of the fourth transistor is supplied with a second predetermined voltage that maximizes the effect of suppressing fluctuations in the transconductance of the second transistor and the third transistor.

6. The temperature compensated differential amplifier according to claim 2, wherein the temperature compensation circuit comprises a fourth transistor whose on-resistance has a positive temperature coefficient and a third resistor whose on-resistance has a positive temperature coefficient, the fourth transistor has a second terminal connected to the power supply and a third terminal connected to one end of the third resistor, the third resistor has the other end connected to the second terminal of the first transistor, and a second predetermined voltage that maximizes the effect of suppressing fluctuations in the transconductance of the second transistor and the third transistor is supplied to the first terminal of the fourth transistor.

7. The temperature compensated differential amplifier according to claim 2, wherein the temperature compensation circuit comprises a fourth transistor whose on-resistance has a positive temperature coefficient, a third resistor having a positive temperature coefficient, and a fourth resistor having a positive temperature coefficient, one end of the fourth resistor connected to the power supply and the other end connected to the second terminal of the fourth transistor, a third terminal of the fourth transistor connected to one end of the third resistor, and the other end of the third resistor connected to the second terminal of the first transistor, and a second predetermined voltage that maximizes the effect of suppressing fluctuations in the transconductance of the second transistor and the third transistor is supplied to the first terminal of the fourth transistor.

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