Differential amplifier

Abstract

A differential amplifier comprising a pair of transistors and a resistor connected to each of the pair of transistors, wherein the resistor exhibits thermal characteristics that compensate for temperature-induced changes in the differential amplification gain.

Description

Differential Amplifier

[0001] This application claims priority from Japanese Patent Application No. 2024-027352, filed on February 27, 2024, the contents of which are incorporated herein by reference.

[0002] As is well known, a differential amplifier is one type of amplifier. This differential amplifier includes, for example, a pair of transistors having emitter terminals connected to each other, a constant current source connected to the emitter terminals, and a pair of collector resistors connected to the collector terminals of the pair of transistors. There is also a variant of the differential amplifier that includes, in addition to the above-mentioned circuit elements, an emitter resistor between each pair of emitter terminals and the constant current source. Patent Document 1 listed below discloses a variable gain amplifier, which is one type of such a differential amplifier circuit.

[0003] Japanese Patent Application Publication No. 2000-332554

[0004] In the differential amplifier of the background art, the gain is determined by the conductance of a pair of transistors and the resistance values ​​of a pair of collector resistors. This background art employs a pair of collector resistors whose resistance values ​​remain constant regardless of fluctuations in ambient temperature, and also employs a constant current source whose current remains constant regardless of fluctuations in ambient temperature.

[0005] That is, in a conventional differential amplifier, the saturation amplitude of the differential output signal and the output voltage level when a common-mode signal is input are determined by the product of the resistance values ​​of the pair of collector resistors and the constant current, and therefore, for example, changing the constant current will change the saturation amplitude and the output voltage level.

[0006] When the constant current is constant regardless of fluctuations in ambient temperature, the conductance of the pair of transistors through which the constant current flows decreases as the ambient temperature rises, and therefore the gain of the differential amplifier decreases as the ambient temperature rises. Therefore, conventional differential amplifiers have the problem that the differential amplification gain fluctuates due to changes in ambient temperature.

[0007] The present invention has been made in view of the above circumstances, and has an object to provide a differential amplifier that can suppress fluctuations in differential amplification gain caused by changes in ambient temperature.

[0008] A differential amplifier according to a first aspect of the present invention comprises a pair of transistors and resistors connected to the pair of transistors, each of the resistors having a temperature characteristic that compensates for temperature changes in differential amplification gain.

[0009] A second aspect of the present invention is a differential amplifier according to the first aspect, wherein the resistors are a first resistor and a second resistor, one end of which is connected to the positive phase output terminals of the pair of transistors, the other end of the first resistor and the other end of the second resistor are connected, and a constant current source is connected to the other end of the first resistor and the other end of the second resistor.

[0010] A third aspect of the present invention is a differential amplifier according to the first aspect, further comprising a first constant current source connected to the positive phase output terminal of one of the pair of transistors and a second constant current source connected to the positive phase output terminal of the other of the pair of transistors, and the resistor is a common resistor having one end connected to the positive phase output terminal of the one of the pair of transistors and the other end connected to the positive phase output terminal of the other of the pair of transistors.

[0011] A fourth aspect of the present invention is a differential amplifier according to the third aspect, wherein the common resistor comprises a plurality of element resistors connected in series, and an open / close switch is connected in parallel to each of the plurality of element resistors.

[0012] A differential amplifier according to a fifth aspect of the present invention is the third aspect, wherein the common resistor comprises a plurality of element resistors connected in parallel, and an open / close switch is connected in series to each of the plurality of element resistors.

[0013] A differential amplifier according to a sixth aspect of the present invention is any one of the first to fifth aspects, wherein the pair of transistors are N-channel bipolar transistors, and the temperature characteristic is such that the resistance value of the resistor decreases as the ambient temperature increases.

[0014] According to an aspect of the present invention, it is possible to provide a differential amplifier that can suppress fluctuations in differential amplification gain caused by changes in ambient temperature.

[0015] Fig. 1 is a circuit diagram showing the configuration of a differential amplifier according to a first embodiment of the present invention; Fig. 2 is a characteristic diagram showing the characteristics of the differential amplifier according to the first embodiment of the present invention; Fig. 3 is a circuit diagram showing the operation of the differential amplifier according to the first embodiment of the present invention; Fig. 4 is a circuit diagram showing the configuration of a differential amplifier according to a second embodiment of the present invention; Fig. 5 is a circuit diagram showing the configuration of a differential amplifier according to a third embodiment of the present invention; Fig. 6 is a circuit diagram showing the configuration of a differential amplifier according to a fourth embodiment of the present invention;

[0016] First to fourth embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] First, the first embodiment will be described with reference to Figures 1 and 2. As shown in Figure 1, a differential amplifier A according to the first embodiment includes a pair of input terminals 1p, 1n, a pair of transistors 2p, 2n, a pair of emitter resistors 3p, 3n, a constant current source 4, a pair of collector resistors 5p, 5n, and a pair of output terminals 6p, 6n.

[0017] A pair of input terminals 1p, 1n are connection terminals for inputting a positive-phase input signal Vin_P and a negative-phase input signal Vin_N from the outside to the differential amplifier A. The positive-phase input signal Vin_P is a high-frequency signal in a predetermined frequency band, and the negative-phase input signal Vin_N is a negative-phase high-frequency signal that has the same frequency as the positive-phase input signal Vin_P but is inverted in phase.

[0018] Of this pair of input terminals 1p, 1n, one input terminal 1p is a positive-phase input terminal for inputting the positive-phase input signal Vin_P to the differential amplifier A. This positive-phase input terminal 1p is connected to a signal source of the positive-phase input signal Vin_P outside the differential amplifier A, and is also connected to the base terminal of one transistor 2p inside the differential amplifier A.

[0019] The other input terminal 1n is an inverting input terminal for inputting the inverting input signal Vin_N to the differential amplifier A. This inverting input terminal 1n is connected to a signal source of the inverting input signal Vin_N outside the differential amplifier A, and is also connected to the base terminal of the other transistor 2n inside the differential amplifier A.

[0020] As shown in the figure, the pair of transistors 2p and 2n are, for example, N-channel bipolar transistors, each of which has a base terminal that functions as an input terminal, an emitter terminal that functions as a positive-phase output terminal, and a collector terminal that functions as a negative-phase output terminal.

[0021] Of this pair of transistors 2p, 2n, one transistor 2p has a base terminal connected to the positive phase input terminal 1p, an emitter terminal connected to one end of one emitter resistor 3p, and a collector terminal connected to one end of one collector resistor 5p and one output terminal 6p.

[0022] The other transistor 2n has a base terminal connected to the inverting input terminal 1n, an emitter terminal connected to one end of the other emitter resistor 3n, and a collector terminal connected to one end of the other collector resistor 5n and the other output terminal 6n.

[0023] The pair of emitter resistors 3p, 3n have the same predetermined resistance value. That is, the resistance value of one emitter resistor 3p (first emitter resistance value) is set to be the same as the resistance value of the other emitter resistor 3n (second emitter resistance value). Note that one emitter resistor 3p corresponds to the first resistor in this embodiment, and the other emitter resistor 3n corresponds to the second resistor in this embodiment.

[0024] One end of one emitter resistor 3p is connected to the emitter terminal of one transistor 2p, and the other end is connected to the input terminal of constant current source 4 and the other end of the other emitter resistor 3n. Also, one end of the other emitter resistor 3n is connected to the emitter terminal of the other transistor 2n, and the other end is connected to the input terminal of constant current source 4 and the other end of one emitter resistor 3p.

[0025] That is, the other end of each of the pair of emitter resistors 3p, 3n is commonly connected to the inflow terminal of the constant current source 4. Furthermore, the pair of emitter resistors 3p, 3n is a resistor connected to the emitter terminals, i.e., the positive phase output terminals, of the pair of transistors 2p, 2n.

[0026] The constant current source 4 is a two-terminal element having an inflow terminal and an outflow terminal. The inflow terminal of this constant current source 4 is commonly connected to the other end of one emitter resistor 3p and the other end of the other emitter resistor 3n, and the outflow terminal is connected to a reference potential (GND). The constant current source 4 flows a predetermined reference current from the inflow terminal to the outflow terminal.

[0027] The pair of collector resistors 5p, 5n have the same predetermined resistance value, i.e., the resistance value of one collector resistor 5p (first collector resistance value) is set to be the same as the resistance value of the other collector resistor 5n (second collector resistance value).

[0028] One end of one collector resistor 5p is connected to the collector terminal of one transistor 2p and one output terminal 6p, and the other end is connected to a power supply Vcc of a predetermined voltage. Also, one end of one collector resistor 5n is connected to the collector terminal of the other transistor 2n and the other output terminal 6n, and the other end is connected to the above-mentioned power supply Vcc. Such a pair of collector resistors 5p, 5n are resistors connected to the collector terminals of the pair of transistors 2p, 2n, i.e., the opposite-phase output terminals.

[0029] A pair of output terminals 6p, 6n are connection terminals for outputting a negative-phase output signal Vout_N and a positive-phase output signal Vout_P to an external subsequent circuit from the differential amplifier A. The positive-phase output signal Vout_P is a high-frequency signal obtained by differentially amplifying the positive-phase input signal Vin_P and the negative-phase input signal Vin_N by the differential amplifier A.

[0030] On the other hand, the negative-phase output signal Vout_N is a high-frequency signal obtained by differentially amplifying the positive-phase input signal Vin_P and the negative-phase input signal Vin_N in the differential amplifier A, and is also a negative-phase high-frequency signal whose phase is inverted relative to the positive-phase output signal Vout_P.

[0031] One output terminal 6p is connected to the collector terminal (negative-phase output terminal) of one transistor 2p inside the differential amplifier A, and is connected to a subsequent circuit outside the differential amplifier A. Such one output terminal 6p outputs a negative-phase output signal Vout_N to the subsequent circuit.

[0032] The other output terminal 6n is connected to the collector terminal (negative-phase output terminal) of the other transistor 2n inside the differential amplifier A, and is connected to a subsequent circuit outside the differential amplifier A. Such other output terminal 6n outputs a positive-phase output signal Vout_P to the subsequent circuit.

[0033] In the differential amplifier A according to the first embodiment, the gain (differential amplification gain) is determined by the conductance of each of the pair of transistors 2p and 2n and the resistance values ​​(first collector resistance value and second collector resistance value) of the pair of collector resistors 5p and 5n. Since the conductance of each of the pair of transistors 2p and 2n decreases as the ambient temperature increases, the differential amplification gain tends to decrease as the ambient temperature increases.

[0034] In order to compensate for such temperature changes in the differential amplification gain, the pair of emitter resistors 3p, 3n in the first embodiment have the temperature characteristics shown in Fig. 2. That is, the pair of emitter resistors 3p, 3n employed in the first embodiment are temperature-dependent resistors whose resistance value tends to decrease as the ambient temperature increases.

[0035] Generally, resistors used in differential amplifiers have as flat a temperature characteristic as possible, that is, their resistance value does not change with fluctuations in ambient temperature. However, the differential amplifier A according to the first embodiment uses a pair of emitter resistors 3p, 3n having temperature characteristics in which their resistance value decreases with an increase in ambient temperature, so as to compensate for temperature changes in the gain (differential amplification gain) of the pair of transistors 2p, 2n.

[0036] Next, the operation of the differential amplifier A according to the first embodiment will be described in detail with reference to the circuit diagram shown in FIG.

[0037] The operation of this differential amplifier A can be shown as in Fig. 3. In Fig. 3, "gm1" is the conductance (first conductance) of one transistor 2p, "gm2" is the conductance (second conductance) of the other transistor 2n, "Re1" is the first emitter resistance value, and "Re2" is the second emitter resistance value.

[0038] Furthermore, "Rc1" is the first collector resistance value, "Rc2" is the second collector resistance value, "I1" is the collector current (first collector current) of one transistor 2p, "I2" is the collector current (second collector current) of the other transistor 2n, and "Iref" is the reference current of the constant current source 4.

[0039] Regarding such a differential amplifier A, the differential gain is calculated under the condition that the positive-phase input signal Vin_P and the negative-phase input signal Vin_N are set to the same voltage, that is, the reference voltage Vref (balanced state). Ｔ ", the first conductance gm1 and the second conductance gm2 are expressed by the following equation (1).

[0040]

[0041] In this equation (1), the potential voltage V Ｔ is defined as given by equation (2). In this equation (2), "q" is the elementary charge (elementary charge) and is 1.6 × 10 －１９ In equation (2), "k" is the Boltzmann constant and "T" is the ambient temperature.

[0042] Here, when the voltage of the positive-phase input signal Vin_P input to one transistor 2p increases by ΔVin from the initial value, the following equation (3) holds.

[0043]

[0044] In this equation (3), "ΔI1" is the amount of change in the first collector current I1 flowing through one transistor 2p, and "ΔI2" is the amount of change in the second collector current I2 flowing through the other transistor 2n. Also, "ΔVbe1" is the amount of change in the base-emitter voltage (first base-emitter voltage Vbe1) of one transistor 2p, and "ΔVbe2" is the amount of change in the base-emitter voltage (second base-emitter voltage Vbe2) of the other transistor 2n.

[0045] In an equilibrium state, the first base-emitter voltage Vbe1 is equal to the second base-emitter voltage Vbe2. When the first emitter resistance Re1 and the second emitter resistance Re2 are set to the same emitter resistance Re, the above equation (3) can be expressed as the following equation (4).

[0046]

[0047] As is well known, the change ΔVbe in the base-emitter voltage Vbe of a bipolar transistor is obtained by dividing the change ΔI1 in the collector current by the conductance gm. In other words, the relationship ΔVbe=ΔI1 / gm holds between the change ΔVbe, the change ΔI1, and the conductance gm. Therefore, the above equation (4) can be expressed as the following equation (5).

[0048]

[0049] Furthermore, the change ΔI1 in the first collector current I1 and the change ΔI2 in the second collector current I2 are related by the following equation using the change ΔI in the collector current: ΔI1=-ΔI2=ΔI. Therefore, the above equation (5) can be expressed as the following equation (6).

[0050]

[0051] When the first collector resistance Rc1 and the second collector resistance Rc2 are set to the same collector resistance Rc, the voltage change ΔVout of the positive phase output signal Vout_P and the negative phase output signal Vout_N is expressed by the output relation ΔVout=ΔI×Rc based on the collector resistance Rc and the change ΔI in the collector current. Therefore, when equation (1) is also taken into consideration, equation (6) becomes the following equation (7).

[0052]

[0053] By modifying this equation (7), the following gain equation (8) is obtained for the differential amplification gain Gain of the differential amplifier A, which includes the emitter resistance value Re as a variable.

[0054]

[0055] This gain equation (8) shows that the differential amplification gain Gain changes depending on the ambient temperature T. That is, the differential amplification gain Gain has a temperature characteristic in which it decreases as the ambient temperature T increases and increases as the ambient temperature T decreases. This gain equation (8) also shows that the differential amplification gain Gain decreases as the emitter resistance value Re increases, and increases as the emitter resistance value Re decreases.

[0056] In the differential amplifier A according to the first embodiment, in response to such temperature characteristics of the differential amplification gain Gain, a pair of emitter resistors 3p, 3n is employed which have temperature characteristics in which the first emitter resistance value and the second emitter resistance value decrease as the ambient temperature T increases, as shown in Fig. 2. Such a differential amplifier A can suppress a decrease in the differential amplification gain Gain when the ambient temperature T increases.

[0057] That is, in the differential amplifier A according to the first embodiment, the pair of emitter resistors 3p, 3n connected to the emitter terminals (positive phase output terminals) of the pair of transistors 2p, 2n, respectively, have temperature characteristics that compensate for temperature changes in the differential amplification gain, and therefore it is possible to suppress fluctuations in the differential amplification gain due to changes in the ambient temperature T.

[0058] Second Embodiment Next, a second embodiment of the present invention will be described with reference to Fig. 4. In this second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals.

[0059] 4, the differential amplifier B according to the second embodiment differs from the differential amplifier A according to the first embodiment in the circuit configuration on the emitter terminal side (positive phase output end side) of the pair of transistors 2p, 2n. That is, the differential amplifier B includes a common emitter resistor 3pn and a pair of constant current sources 4p, 4n instead of the pair of emitter resistors 3p, 3n and constant current source 4 in the differential amplifier A.

[0060] In a pair of transistors 2p, 2n, the emitter terminal of one transistor 2p is connected to one end of a common emitter resistor 3pn and to the input terminal of one constant current source 4p, and the emitter terminal of the other transistor 2n is connected to the other end of the common emitter resistor 3pn and to the input terminal of the other constant current source 4n.

[0061] The common emitter resistor 3pn has a predetermined resistance value, one end connected to the emitter terminal of one transistor 2p and the inflow terminal of one constant current source 4p, and the other end connected to the emitter terminal of the other transistor 2n and the inflow terminal of the other constant current source 4n. Like the pair of emitter resistors 3p, 3n in the first embodiment, this common emitter resistor 3pn has temperature characteristics in which the emitter resistance value decreases as the ambient temperature T increases.

[0062] One of the constant current sources 4p is a two-terminal element having an inflow terminal and an outflow terminal, and passing a predetermined reference current from the inflow terminal to the outflow terminal. The inflow terminal of this constant current source 4p is connected to the emitter terminal of one of the transistors 2p and one end of the common emitter resistor 3pn, and the outflow terminal is connected to the reference potential (GND).

[0063] The other constant current source 4n, like the first constant current source 4p, is a two-terminal element having an inflow terminal and an outflow terminal, and passing a predetermined reference current from the inflow terminal to the outflow terminal. The inflow terminal of this constant current source 4n is connected to the emitter terminal of the other transistor 2n and the other end of the common emitter resistor 3pn, and the outflow terminal is connected to the reference potential (GND).

[0064] The common emitter resistor 3pn corresponds to the common resistor in this embodiment. The constant current source 4p corresponds to the first constant current source in this embodiment. The other constant current source 4n corresponds to the second constant current source in this embodiment.

[0065] For this differential amplifier B, the relationship between the differential amplification gain and temperature and the relationship between the differential amplification gain and the resistance value of the common emitter resistor 3pn also show the same tendency as the above-mentioned gain equation (8). The common emitter resistor 3pn in this differential amplifier B has temperature characteristics such that the emitter resistance value decreases as the ambient temperature T increases. That is, in the second embodiment, the common emitter resistor 3pn connected to the pair of transistors 2p, 2n has temperature characteristics that compensate for temperature changes in the differential amplification gain.

[0066] Therefore, in the differential amplifier B of the second embodiment, the common emitter resistor 3pn connected to each of the emitter terminals (positive phase output terminals) of the pair of transistors 2p and 2n has temperature characteristics that compensate for temperature changes in the differential amplification gain, making it possible to suppress fluctuations in the differential amplification gain caused by changes in the ambient temperature T.

[0067] Furthermore, while the differential amplifier A according to the first embodiment includes a pair of emitter resistors 3p and 3n, the differential amplifier B according to the second embodiment includes a single common emitter resistor 3pn, meaning that the number of emitter resistors in this differential amplifier B can be reduced compared to the first embodiment.

[0068] Third Embodiment Next, a third embodiment of the present invention will be described with reference to Fig. 5. In this third embodiment, the same components as those in the second embodiment are denoted by the same reference numerals.

[0069] 5, in the differential amplifier C according to the third embodiment, the common emitter resistor 3pn in the second embodiment is composed of a plurality of series element circuits U1, U2, ..., Ui, where "i" in the third embodiment is a natural number equal to or greater than 3.

[0070] Each of the series element circuits U1, U2, ..., Ui includes an element resistor k1, k2, ..., ki having a predetermined resistance value, and element open / close switches s1, s2, ..., si connected in parallel to the element resistor k1, k2, ..., ki, respectively.

[0071] For example, the first series element circuit U1 is composed of a first element resistor k1 and a first element switch s1 connected in parallel to the first element resistor k1. The second series element circuit U2 is composed of a second element resistor k2 and a second element switch s2 connected in parallel to the second element resistor k2. (Omitted) The i-th element circuit Ui is composed of an i-th series element resistor ki and an i-th element switch si connected in parallel to the i-th element resistor ki.

[0072] That is, the common emitter resistor 3pn in the third embodiment has a plurality of element resistors k1, k2, ..., ki connected in series, and open / close switches s1, s2, ..., si are respectively connected in parallel to the element resistors k1, k2, ..., ki.

[0073] In such a differential amplifier C, the resistance value of the common emitter resistor 3pn can be variably set according to the open / close states of the plurality of element open / close switches s1, s2, ..., si. That is, the differential amplifier C according to the third embodiment not only suppresses fluctuations in the differential amplification gain caused by changes in the ambient temperature T, but also makes it possible to switch the differential amplification gain between multiple levels.

[0074] Fourth Embodiment Next, a fourth embodiment of the present invention will be described with reference to Fig. 6. In this fourth embodiment, the same components as those in the second embodiment are denoted by the same reference numerals.

[0075] 6, in the differential amplifier D according to the fourth embodiment, the common emitter resistor 3pn in the second embodiment is composed of a plurality of parallel element circuits W1, W2, ..., Wm, where "m" in the fourth embodiment is a natural number equal to or greater than 3.

[0076] Each of the parallel element circuits W1, W2, ..., Wm includes an element resistor y1, y2, ..., ym having a predetermined resistance value, one-end open / close switches w1p, w2p, ..., wmp connected in series to one end of the element resistor y1, y2, ..., ym, and other-end open / close switches w1n, w2n, ..., wmn connected in series to the other end of the element resistor y1, y2, ..., ym.

[0077] For example, the first parallel element circuit W1 is composed of a first element resistor y1, a first one-end open / close switch w1p connected in series to one end of the first element resistor y1, and a first other-end open / close switch w1n connected in series to the other end of the first element resistor y1. The second parallel element circuit W2 is composed of a second element resistor y2, a second one-end open / close switch w2p connected in series to one end of the second element resistor y2, and a second other-end open / close switch w2n connected in series to the other end of the second element resistor y2.

[0078] (Omitted) The mth parallel element circuit Wm is composed of the mth element resistor ym, the mth one-end open / close switch wmp connected in series to one end of the mth element resistor ym, and the mth other-end open / close switch wmn connected in series to the other end of the mth element resistor ym.

[0079] The multiple one-end switches w1p, w2p, ..., wmp and the multiple other-end switches w1n, w2n, ..., wmn are element switches that are set to the same state. For example, when the first one-end switch w1p is set to an open state, the first other-end switch w1n is also set to an open state. Also, when the first one-end switch w1p is set to a closed state, the first other-end switch w1n is also set to a closed state.

[0080] That is, the common emitter resistor 3pn in the fourth embodiment has a plurality of element resistors y1, y2, ..., ym connected in parallel, and one end open / close switches w1p, w2p, ..., wmp and the other end open / close switches w1n, w2n, ..., wmn are each connected in series to the element resistors y1, y2, ..., ym.

[0081] In such a differential amplifier D, the resistance value of the common emitter resistor 3pn can be variably set according to the open / close states of the plurality of one-end open / close switches w1p, w2p, ..., wmp and the plurality of other-end open / close switches w1n, w2n, ..., wmn. That is, the differential amplifier D according to the fourth embodiment not only suppresses fluctuations in the differential amplification gain caused by changes in the ambient temperature T, but also makes it possible to switch the differential amplification gain between multiple levels.

[0082] The present invention is not limited to the above embodiment, and the following modifications are possible, for example: (1) In the above embodiment, among the resistors connected to the pair of transistors 2p and 2n, the pair of emitter resistors 3p and 3n or the common emitter resistor 3pn connected to the emitter terminals (positive phase output terminals) of the pair of transistors 2p and 2n are provided with temperature characteristics that compensate for temperature changes in the differential amplification gain, but the present invention is not limited to this.

[0083] As shown in the gain equation (8) above, instead of the pair of emitter resistors 3p, 3n or the common emitter resistor 3pn connected to the emitter terminals (positive-phase output terminals) of the pair of transistors 2p, 2n, the pair of collector resistors 5p, 5n connected to the collector terminals (negative-phase output terminals) of the pair of transistors 2p, 2n may be given temperature characteristics that compensate for temperature changes in the differential amplification gain.

[0084] Furthermore, if necessary, in addition to the pair of emitter resistors 3p, 3n or common emitter resistor 3pn connected to the emitter terminals (positive-phase output terminals) of the pair of transistors 2p, 2n, the pair of collector resistors 5p, 5n connected to the collector terminals (negative-phase output terminals) of the pair of transistors 2p, 2n may also be given temperature characteristics that compensate for temperature changes in the differential amplification gain.

[0085] (2) In the above embodiment, N-channel bipolar transistors are used as the pair of transistors, but this is not limiting. The present invention is also applicable to a pair of P-channel bipolar transistors. Furthermore, the present invention is also applicable to transistors other than bipolar transistors, such as various field-effect transistors (unipolar transistors).

[0086] (3) In the above embodiment, a differential amplifier having the simplest circuit configuration has been described, but the present invention is not limited to this. For example, the present invention can be applied to differential amplifier circuits of various circuit configurations, such as a circuit configuration including a pair of output transistors each cascode-connected to a pair of transistors.

[0087] A, B, C, D... differential amplifier, 1p, 1n... input terminal, 2p, 2n... transistor, 3p, 3n... emitter resistor, 3pn... common emitter resistor, 4, 4p, 4n... constant current source, 5p, 5n... collector resistor, 6p, 6n... output terminal

Claims

1. A differential amplifier comprising a pair of transistors and resistors connected to each of the pair of transistors, wherein the resistors have temperature characteristics that compensate for temperature changes in differential amplification gain.

2. The differential amplifier according to claim 1, wherein the resistors are a first resistor and a second resistor, one end of which is connected to the positive output terminal of the pair of transistors, the other end of the first resistor and the other end of the second resistor are connected, and a constant current source is connected to the other end of the first resistor and the other end of the second resistor.

3. The differential amplifier according to claim 1, further comprising: a first constant current source connected to the positive phase output terminal of one of the pair of transistors; and a second constant current source connected to the positive phase output terminal of the other of the pair of transistors; and the resistor is a common resistor having one end connected to the positive phase output terminal of the one of the pair of transistors and the other end connected to the positive phase output terminal of the other of the pair of transistors.

4. A differential amplifier according to claim 3, wherein the common resistor comprises a plurality of element resistors connected in series, and an open / close switch is connected in parallel to each of the plurality of element resistors.

5. A differential amplifier according to claim 3, wherein said common resistor comprises a plurality of element resistors connected in parallel, and an open / close switch is connected in series to each of said plurality of element resistors.

6. A differential amplifier according to any one of claims 1 to 5, wherein the pair of transistors are N-channel bipolar transistors, and the temperature characteristic is such that the resistance value of the resistor decreases as the ambient temperature increases.

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