JP5864657B2 - Constant current circuit - Google Patents

Description

  The present invention relates to a constant current circuit, and more particularly to a constant current circuit using a bipolar transistor.

  In a semiconductor integrated circuit such as an analog IC (IC: integrated circuit), a reference voltage or a constant current as a reference is often required to realize a required function. As a method for obtaining a reference voltage or a constant current, there is a method in which a reference voltage generated by an external power supply device or the like is directly applied to an IC. However, in this method, it is necessary to prepare an external power supply device separately from the IC, and mounting on a printed circuit board becomes complicated. Therefore, in many ICs, a reference voltage generation circuit for generating a reference voltage, a constant current circuit for generating a constant current, and the like are formed in the IC, and the reference voltage and the constant current generated by these circuits are generated in the IC. By supplying to other functional circuits, the intended function is realized.

  As a conventional example of such a reference voltage generation circuit and a constant current circuit, for example, Non-Patent Document 1 discloses a circuit using a bipolar transistor.

P. R. Gray / R. G. Co-authored by Mayer, directed by Atsushi Nagata, “Analog Integrated Circuit Design Technology”, first edition published November 30, 1990, Baifukan, pp. 224-225, FIG. 4.7.

  In general, the reference voltage and constant current generated inside the IC affect the circuit characteristics of the functional circuit inside the IC to which it is supplied, so it is highly resistant to variations (process variations) and temperature variations due to manufacturing processes. Is required. However, the constant current circuit disclosed in Non-Patent Document 1 has a problem that it is easily affected by process fluctuations, temperature fluctuations, and the like. This will be described in detail below.

  FIG. 5 is a diagram showing a circuit configuration of the constant current circuit 60 disclosed in Non-Patent Document 1. As shown in FIG. As shown in the figure, the constant current circuit 60 includes a voltage generation circuit 61 that generates a reference voltage Vp and a current generation circuit 62 that generates a constant current Ip based on the reference voltage Vp.

  In the constant current circuit 60, the reference voltage Vp and the current Ip can be expressed by Expression (1) and Expression (2), respectively. Here, VCC represents the power supply voltage on the high potential side, VEE represents the power supply voltage on the low potential side, and VBE represents the base-emitter voltage of the bipolar transistors Qx and Qy. Further, the high-potential-side power supply voltage VCC is set to the ground voltage (VCC = 0V), the low-potential-side power supply voltage VEE is set to the negative voltage (VEE <0V), and the base-emitter voltages of the bipolar transistors Qx and Qy are equal. Shall.

  As understood from the above equation (2), the current Ip generated by the constant current circuit 60 depends on the base-emitter voltage VBE of the bipolar transistors Qx and Qy. Since the base-emitter voltage VBE of the bipolar transistor is affected by process variations and temperature variations, the current Ip also varies due to process variations and temperature variations. As a result, the characteristics of various functional circuits that use the current Ip inside the IC may vary.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a constant current circuit that is less susceptible to process variations and temperature variations in a semiconductor integrated circuit.

  The constant current circuit according to the present invention includes a first power supply line (VCC) to which a first power supply voltage is supplied, a second power supply line (VEE) to which a second power supply voltage is supplied, and a first bipolar having a diode connection. A transistor, a second bipolar transistor having a diode connection and connected in series to the first bipolar transistor; a node to which the first bipolar transistor and the second bipolar transistor are connected; and the first power supply line; The first resistor (R1) connected in series with the first bipolar transistor, a node connected to the first bipolar transistor and the second bipolar transistor, and the second power supply line. A second resistor (R2) connected in series with the second bipolar transistor, and an input terminal connected to the first bipolar transistor. An emitter follower circuit connected to a node to which a second transistor and a second bipolar transistor are connected, a third bipolar transistor having a base electrode connected to an output terminal of the emitter follower circuit, and an emitter of the third bipolar transistor And an output resistor connected between the electrode and the second power supply line.

  In the constant current source circuit, the emitter follower circuit has a collector electrode supplied with current from the first power supply line, and a base electrode connected to a node to which the first bipolar transistor and the second bipolar transistor are connected. A third bipolar transistor, and a third resistor connected between the emitter electrode of the third bipolar transistor and the second power supply line.

  The constant current source circuit includes a plurality of the first bipolar transistors, each of the first bipolar transistors connected in series, a plurality of the second bipolar transistors, and each of the second bipolar transistors connected in series. It may be connected.

  In the constant current circuit, the number of serially connected first bipolar transistors is m, the number of serially connected second bipolar transistors is n, the resistance value of the first resistor is R1, and the resistance value R2 of the second resistor. Sometimes, the following formula (A) may be satisfied.

  Another constant current circuit according to the present invention includes a first power supply line to which a first power supply voltage is supplied, a second power supply line to which a second power supply voltage is supplied, the first power supply line, and the second power supply line. A first resistor (Ra1) and a second resistor (Ra2) connected in series with each other, a third resistor (Rb2) having one end connected to the second power supply line, and the other end of the third resistor The first bipolar transistor (Q41 to Q4m) having a diode connection and a node to which the third resistor and the first bipolar transistor are connected and the first power supply line are connected to the first bipolar transistor. A fourth resistor (Rb1) connected in series with the transistor and a node (A) having a pair of differential input terminals and one of the differential input terminals connected to the first resistor and the second resistor Connected to the other A differential amplifier circuit whose dynamic input terminal is connected to a node (B) to which the third resistor and the first bipolar transistor are connected, and an emitter follower whose input terminal is connected to the output terminal of the differential amplifier circuit A circuit, a second bipolar transistor (Qc) having a base electrode connected to an output terminal of the emitter follower circuit, an output resistor connected between the emitter electrode of the second bipolar transistor and the second power supply line In the constant current source circuit, the differential amplifier circuit includes a third bipolar transistor (Q3) having a base electrode connected to a node (A) to which the first resistor and the second resistor are connected. A fourth bipolar transistor (Q4) having a base electrode connected to the other end of the fourth resistor, the first power supply line, and the third bipolar transistor. A fifth resistor (Rc1) connected between the collector electrode of the transistor and a sixth resistor (Rc2) connected between the first power supply line and the collector electrode of the fourth bipolar transistor; A seventh resistor (Re1) and an eighth resistor (Re2) connected in series between the emitter electrode of the transistor and the emitter electrode of the fourth transistor, and the seventh resistor and the eighth resistor are connected. A fifth bipolar transistor (Q5) having a collector electrode connected to the node and a base electrode connected to the output terminal of the emitter follower circuit, and being connected between the emitter electrode of the fifth bipolar transistor and the second power supply line And a ninth resistor (Rg1).

  In the constant current circuit, the emitter follower circuit includes a sixth bipolar transistor (Q6) in which a current is supplied to the collector electrode from the first power supply line, and a collector electrode of the fourth bipolar transistor is connected to a base electrode; A tenth resistor (Rd1) having one end connected to the emitter electrode of the sixth bipolar transistor, and a collector electrode and a base electrode connected to the other end of the tenth resistor and the base electrode of the fifth bipolar transistor. And a seventh resistor (Rg2) connected between the emitter electrode of the seventh bipolar transistor and the second power supply line.

  In the constant current circuit, the number of serially connected first bipolar transistors is m, and the bipolar existing in the path from the base electrode of the sixth bipolar transistor to the seventh power source through the seventh bipolar transistor and the eleventh resistor. The number of transistors is n, the resistance value of the fourth resistor is Rb1, the resistance value of the third resistor is Rb2, the resistance values of the fifth resistor and the sixth resistor are Rc, the seventh resistor and the eighth resistor When the resistance value is Re, the following formula (B) may be satisfied.

  Note that the reference numerals in parentheses in the above description merely exemplify what are included in the concept of the components indicated by the reference numerals in the drawings.

  According to the present invention, it is possible to realize a constant current circuit that is hardly affected by process variations and temperature variations.

It is a figure which shows the structure of the constant current source circuit which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the constant current source circuit which concerns on Embodiment 2 of this invention. It is a figure which shows the small signal characteristic of the constant current source circuit which concerns on Embodiment 2. FIG. It is a figure which shows the small signal characteristic of the conventional constant current source circuit. It is a figure which shows the structure of the conventional constant current source circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<< Embodiment 1 >>
FIG. 1 shows a configuration of a constant current circuit according to Embodiment 1 of the present invention.
The constant current circuit 100 shown in the figure generates a constant current Ic under the condition that the power supply voltage is fixed.

  Although not particularly limited, the constant current circuit 100 can be realized, for example, by a semiconductor integrated circuit formed on a semiconductor substrate by a known HBT (Heter Junction Bipolar Transistor) manufacturing process. The constant current circuit 100 may be realized as a one-chip semiconductor device or may be realized as a multi-chip semiconductor device, and is not particularly limited.

  Specifically, the constant current circuit 100 includes a voltage generation circuit 1, an emitter follower circuit 2, and a current generation circuit 3. The voltage generation circuit 1 and the emitter follower circuit 2 operate between the power supply voltage VCC and the power supply voltage VEE, and the current generation circuit 3 generates a constant current Ic with reference to the power supply voltage VEE.

  In the following description, reference numerals VCC and VEE represent not only power supply voltages but also power supply lines to which those power supply voltages are supplied. Further, the case where the high-potential-side power supply voltage VCC is set to the ground voltage (= 0V) and the low-potential-side power supply voltage VEE is set to the negative voltage (<0V) will be described as an example. .

First, the voltage generation circuit 1 will be described.
The voltage generation circuit 1 generates a voltage based on the forward voltage of the PN junction. Specifically, the voltage generation circuit 1 includes transistor groups 10 and 11 and resistors R1 and R2.

  The transistor group 10 includes m (m is an integer of 1 or more) NPN bipolar transistors Q11 to Q1m connected in series. Each of bipolar transistors Q11 to Q1m (m is an integer of 1 or more) has a diode connection in which a collector electrode and a base electrode are connected in common. Bipolar transistors Q11 to Q1m are connected in series so that the collector electrode and the base electrode are on the power supply line VCC side and the emitter electrode is on the power supply line VEE side.

  The transistor group 11 includes n (n is an integer of 1 or more) NPN-type Q21 to Q2n connected in series. Each of bipolar transistors Q21 to Q2n has a diode connection in which a collector electrode and a base electrode are connected in common. Bipolar transistors Q21 to Q2n are connected in series so that the collector electrode and the base electrode are on the power supply line VCC side and the emitter electrode is on the power supply line VEE side.

  The bipolar transistors Q11 to Q1n and Q21 to Q2m are HBTs as described above. In the constant current circuit 100, all bipolar transistors including the bipolar transistors Q11 to Q1n and Q21 to Q2m are formed to have the same transistor size, for example, and the base-emitter voltages VBE are equal.

  Transistor group 10 and transistor group 11 are connected in series between power supply line VCC and power supply line VEE via resistors R1 and R2. Specifically, the collector electrode and the base electrode of the transistor Q1m in the transistor group 10 are connected to the power supply line VCC via the resistor R1, and the emitter electrode of the transistor Q21 in the transistor group 11 is connected to the power supply line VEE via the resistor R2. Is done. Further, the emitter electrode of bipolar transistor Q11 in transistor group 10 is connected to the collector electrode and base electrode of bipolar transistor Q2n in transistor group 11. Hereinafter, a node to which the emitter electrode of bipolar transistor Q11 and the base electrode and collector electrode of bipolar transistor Q21 are connected is referred to as node S.

  The resistor R1 is connected in series with the bipolar transistors Q11 to Q1m between the node S and the power supply line VCC. For example, the resistor R1 has one end connected to the power supply line VCC and the other end connected to the collector electrode of the transistor Q1m. The resistor R1 only needs to be connected in series with the bipolar transistors Q11 to Q1m between the power supply line VCC and the node S, and is not limited to the position shown in FIG.

  Resistor R2 is connected in series with bipolar transistors Q21-Q2n between node S and power supply line VEE. For example, the resistor R2 has one end connected to the power supply line VEE and the other end connected to the emitter electrode of the transistor Q21. The resistor R2 only needs to be connected in series with the bipolar transistors Q21 to Q2n between the power supply line VEE and the node S, and is not limited to the position shown in FIG.

Next, the emitter follower circuit 2 will be described.
The emitter follower circuit 2 receives the signal of the node S, amplifies the power, and outputs the amplified signal to the node CS. Specifically, the emitter follower circuit 2 includes bipolar transistors Q30 to Q32 and a resistor R3.

  A current is supplied from the power supply line VCC to the collector electrode of the bipolar transistor Q30. The base electrode of bipolar transistor Q30 is connected to node S.

  Bipolar transistors Q31 and 32 have a diode connection in which a collector electrode and a base electrode are connected in common, and are connected in series between the collector electrode of bipolar transistor Q30 and power supply line VCC. Bipolar transistors Q31 and 32 can limit the voltage applied between the collector electrode and the emitter electrode of bipolar transistor Q30.

  FIG. 1 illustrates the case where two bipolar transistors Q31 and Q32 are inserted between the collector electrode of the bipolar transistor Q30 and the power supply line VCC. However, the number of bipolar transistors to be inserted is the number of bipolar transistors Q30. It can be changed according to the pressure resistance. Further, if the voltage exceeding the breakdown voltage is not applied to the bipolar transistor Q30 even if the collector electrode of the bipolar transistor Q30 is directly connected to the power supply line VCC, the bipolar transistors Q31 and Q32 may be removed.

  Resistor R3 is connected between the emitter electrode of bipolar transistor Q30 and power supply line VEE. Hereinafter, a node to which the emitter electrode of bipolar transistor Q30 and resistor R3 are connected is referred to as node CS.

  According to the emitter follower circuit 2, a voltage lower than the voltage at the node S by the base-emitter voltage VBE of the bipolar transistor Q30 is generated at the node CS. That is, when the base-emitter voltages of the transistors Q11 to Q1n, Q21 to Q2m, and Q30 are VBE, the voltage Vcs of the node CS can be expressed by the following equation (3).

Next, the current generation circuit 3 will be described.
Current generation circuit 3 includes a bipolar transistor Qc and a resistor RE. The base electrode of bipolar transistor Qc is connected to node CS. Resistor RE is connected between the emitter electrode of bipolar transistor Qc and power supply line VEE.

  According to the current generation circuit 3, the current Ic corresponding to the voltage Vcs of the node CS is generated. That is, the current Ic can be expressed by the following formula (4) by the above formula (3).

  As understood from the above equation (4), the current Ic depends on the base-emitter voltage VBE. However, since the coefficient of VBE in the equation (4) is expressed by a polynomial including resistors R1 and R2 and the numbers m and n of the respective transistors constituting the two transistor groups 10 and 11, R1, R2, If the values of m and n are adjusted to satisfy the following equation (5), the VBE coefficient can be made zero. That is, by setting the coefficient of VBE to zero, the output current Ic is determined by the resistors R1, R2, and RE and the power supply voltage VEE, and the influence of the variation of the base-emitter voltage VBE due to process variation and temperature variation is affected. I will not receive it.

  If there are restrictions on the values of R1, R2, m, and n and the VBE coefficient cannot be zero, adjust the values of R1, R2, m, and n so that the VBE coefficient approaches zero. For example, it is possible to reduce the influence of VBE variation on the output current IC.

  As described above, the voltage generation circuit 1 generates a voltage corresponding to the base-emitter voltage VBE (PN junction forward voltage) of the bipolar transistor, and the generated voltage is supplied to the current generation circuit 3 via the emitter follower circuit 2. By supplying the output current Ic, the output current Ic which is hardly affected by the base-emitter voltage VBE can be generated. Thereby, it is possible to realize a constant current circuit that is hardly affected by process fluctuations and temperature fluctuations.

<< Embodiment 2 >>
FIG. 2 is a diagram showing a configuration of a constant current circuit according to Embodiment 2 of the present invention.
Similar to the constant current circuit 100 according to the first embodiment, the constant current circuit 101 according to the second embodiment generates a voltage corresponding to the base-emitter voltage VBE (forward voltage of the PN junction) of the bipolar transistor as an emitter follower circuit. The circuit configuration of the voltage generation circuit that generates a voltage corresponding to the base-emitter voltage VBE (PN junction forward voltage), and the emitter follower circuit The configuration is different.
In the constant current circuit 101, the same components as those of the constant current circuit 100 are denoted by the same reference numerals and detailed description thereof is omitted.

  As shown in FIG. 2, the constant current circuit 101 includes a voltage generation circuit 4, an emitter follower circuit 5, and a current generation circuit 3.

First, the voltage generation circuit 4 will be described.
The voltage generation circuit 4 includes two resistance voltage dividing units 40 and 41 and a differential amplifier circuit 42.
The resistance voltage dividing unit 40 includes resistors Ra1 and Ra2 connected in series between the power supply line VCC and the power supply line VEE. Hereinafter, a node to which the resistor Ra1 and the resistor Ra2 are connected is referred to as a node A.

  The resistor voltage divider 41 includes a transistor group 43 and resistors Rb1 and Rb2. The transistor group 43 includes k (k is an integer of 1 or more) NPN-type Q41 to Q4k connected in series. Each of bipolar transistors Q41 to Q4k has a diode connection in which a collector electrode and a base electrode are connected in common. Bipolar transistors Q41 to Q4k are connected in series so that the collector electrode and the base electrode are on the power supply line VCC side and the emitter electrode is on the power supply line VEE side. In the present embodiment, the case where k = 2 is described as an example.

  The resistor Rb2 is connected between the emitter electrode of the bipolar transistor Q41 constituting the transistor group 43 and the power supply line VEE. Hereinafter, the node where resistor Rb2 and the emitter electrode of bipolar transistor Q41 are connected is referred to as node B.

  Resistor Rb1 is connected in series with bipolar transistors Q41-Q4m between node B and power supply line VCC. For example, the resistor R1b has one end connected to the power supply line VCC and the other end connected to the collector electrode of the transistor Q4k on the high potential side of the transistor group 43. The resistor Rb1 only needs to be connected in series with the bipolar transistors Q41 to Q4k between the power supply line VCC and the node B, and is not limited to the connection position shown in FIG.

  Here, the resistance values of the resistors Ra1, Ra2, Rb1, and Rb2 are set so that the voltage at the node A and the voltage at the node B are substantially equal.

The differential amplifier circuit 42 includes bipolar transistors Q3, Q4, and Q5 and resistors Re1, Re2, Rc1, Rc2, and Rg1.
The base electrode of bipolar transistor Q3 is connected to node A. The base electrode of bipolar transistor Q4 is connected to node B. Resistor Rc1 is connected between power supply line VCC and the collector electrode of bipolar transistor Q3. Resistor Rc2 is connected between power supply line VCC and the collector electrode of bipolar transistor Q4. Hereinafter, a node to which the collector electrode of the bipolar transistor Q4 and the resistor Rc2 are connected is referred to as a node C.

  The resistor Re1 has one end connected to the emitter electrode of the bipolar transistor Q3 and the other end connected to the collector electrode of the bipolar transistor Q5. Resistor Re2 has one end connected to the emitter electrode of bipolar transistor Q4 and the other end connected to the collector electrode of bipolar transistor Q5. Resistor Rg1 is connected between the emitter electrode of bipolar transistor Q5 and power supply line VEE.

Next, the emitter follower circuit 5 will be described.
Emitter follower circuit 5 includes bipolar transistors Q6 and Q7 and resistors Rd1 and Rg2.

  The collector electrode of the bipolar transistor Q6 is supplied with current from the power supply line VCC. The base electrode of bipolar transistor Q6 is connected to node C. Resistor Rd1 has one end connected to the emitter electrode of bipolar transistor Q6 and the other end connected to the collector electrode of bipolar transistor Q7.

The bipolar transistor Q7 has a diode connection in which the collector electrode and the base electrode are connected. The base electrode and collector electrode of bipolar transistor Q7 are connected to the base electrode of bipolar transistor Q5. Hereinafter, a node to which the collector electrode and base electrode of bipolar transistor Q7 and the base electrode of bipolar transistor Q5 are connected is referred to as node CS.
The resistor Rg2 is connected between the emitter electrode of the bipolar transistor Q7 and the power supply line VEE.

  The current generation circuit 3 includes a bipolar transistor Qc and a resistor RE. The base electrode of bipolar transistor Qc is connected to node CS. Resistor RE is connected between the emitter electrode of bipolar transistor Qc and power supply line VEE.

  According to the constant current circuit 101 configured as described above, the current Ic can be derived as follows.

  First, the voltage VA at the node A and the voltage VB at the node B can be expressed by the following equations (6) and (7). In the following description, it is assumed that base-emitter voltages VBE of bipolar transistors Q41 to Q4k, Q5, Q6, Q7, and Qc are equal.

Here, when the voltage VB of the voltage VA and the node B of the node A is assumed to be substantially equal to, approximately, the collector current I _Q4 of the transistor Q4 in the differential amplifier circuit 42, be represented by the following formula (8) Can do. Note that Re1 = Re2 = Re.

  From the equation (8), the voltage VE of the node E to which the emitter electrode of the transistor Q6 in the emitter follower circuit 5 and the resistor Rd1 are connected can be expressed by the equation (9). Note that Rc1 = Rc2 = Rc.

The collector current I _Q7 of the bipolar transistor Q7 may be represented by the formula (10).

Further, the collector current I _Q7 of the bipolar transistor Q7 can also be expressed by Expression (11) from the relationship between the voltage VCS at the node CS, the base-emitter voltage VBE of the bipolar transistor Q7, and the resistor Rg2.

  Similarly, collector current IQ5 of bipolar transistor Q5 can be expressed by equation (12) from the relationship between voltage VCS at node CS, base-emitter voltage VBE of bipolar transistor Q5, and resistor Rg1.

From the equations (11) and (12), the relationship between the collector current I _Q5 of the bipolar transistor _Q5 and the collector current I _Q7 of the bipolar transistor Q7 can be expressed by equation (13).

Therefore, Expression (14) is established for _{IQ 7} by Expression (9), Expression (10), and Expression (13).

The relationship between the collector current I _Q7 and the output current Ic of the bipolar transistor Q7 may be represented by the formula (15).

  Therefore, the output current Ic can be expressed by the equation (16) according to the equations (13) and (14).

  As understood from the above equation (16), the output current Ic depends on the base-emitter voltage VBE. However, since the coefficient of VBE in equation (16) is represented by a polynomial including resistors Rb1, Rb2, Rc, and Re, adjusting the values of Rb1, Rb2, Rc, and Re makes the coefficient of VBE zero. This makes it possible to suppress the influence of fluctuations in VBE on the output current Ic.

  In the constant current circuit 100 according to the first embodiment described above, since the number m and n of the bipolar transistors constituting the transistor groups 10 and 11 can only be an integer, the resistance R1 for making the coefficient of VBE zero. , R2 values are limited. On the other hand, the constant current circuit 101 according to the second embodiment does not depend on the number of transistors constituting the transistor group 40, as can be understood from the above equation (16), and therefore resistances such as Rb1 and Rb2 By adjusting the value, the coefficient of VBE can be made zero.

  If the resistance values of Rb1, Rb2, etc. are limited and the VBE coefficient cannot be made zero, the values of the resistors Rb1, Rb2, Rc, and Re should be adjusted so that the VBE coefficient approaches zero. For example, it is possible to reduce the influence of VBE variation on the output current IC.

  Here, FIG. 3 shows the small signal characteristics of the amplifier when the constant current circuit 101 is applied to a wideband amplifier when the circuit constants such as Rb1 and Rb2 are adjusted so that the VBE coefficient of the constant current circuit 101 is close to zero. Show. As a comparative example, FIG. 4 shows the small signal characteristics of an amplifier when the conventional constant current circuit 60 (FIG. 5) is applied to a broadband amplifier. The small signal characteristics shown in FIG. 3 and FIG. 4 are simulation results by a circuit simulator (SPICE: Simulation Program with Integrated Circuit Emphasis).

  In FIG. 3, reference numeral 200 indicates the frequency characteristic of the gain of the wideband amplifier to which the constant current circuit 101 is applied under the standard condition (typical condition), and reference numeral 201 indicates that the base-emitter voltage VBE of the bipolar transistor is 5%. The frequency characteristic of the gain of the wideband amplifier to which the constant current circuit 101 is applied in the low case is shown. Reference numeral 202 denotes the wideband amplifier to which the constant current circuit 101 to which the base-emitter voltage VBE of the bipolar transistor is 5% higher is applied. Represents frequency characteristics of gain. In FIG. 4, reference numeral 300 represents the frequency characteristic of the gain of the wideband amplifier to which the constant current circuit 60 is applied under standard conditions (typical conditions), and reference numeral 301 represents the base-emitter voltage VBE of the bipolar transistor. The frequency characteristic of the gain of the wideband amplifier to which the constant current circuit 60 is applied when it is 5% lower is shown. Reference numeral 202 denotes a wideband to which the constant current circuit 60 is applied when the base-emitter voltage VBE of the bipolar transistor is 5% higher. It represents the frequency characteristics of the gain of the amplifier.

  As can be seen by comparing the frequency characteristics of the gains in FIGS. 3 and 4, in the conventional constant current circuit 60, the gain of the wideband amplifier largely fluctuates due to the fluctuation of the base-emitter voltage VBE. In the constant current circuit 101 according to the second embodiment, the variation in the gain of the broadband amplifier with respect to the variation in the base-emitter voltage VBE is small. That is, it is understood that the amplifier using the constant current circuit 101 according to the second embodiment is less susceptible to the fluctuation of the base-emitter voltage VBE than the conventional amplifier using the constant current circuit 60. .

  As described above, the voltage generation circuit 4 generates a voltage corresponding to the base-emitter voltage VBE (forward voltage of the PN junction) of the bipolar transistor, and the generated voltage is supplied to the current generation circuit 3 via the emitter follower circuit 5. By supplying the output current Ic, it is possible to generate the output current Ic that is hardly affected by the base-emitter voltage VBE as in the constant current circuit 100 of the first embodiment.

  Further, according to the constant current circuit 101 according to the second embodiment, the coefficient of VBE can be made zero only by adjusting the resistance values of Rb1, Rb2, etc., so that the circuit design becomes easier.

  Although the invention made by the present inventors has been specifically described based on the embodiments, it is needless to say that the present invention is not limited thereto and can be variously modified without departing from the gist thereof. Yes.

  For example, in the constant current circuits 100 and 101, the case where all the bipolar transistors are HBTs has been exemplified, but when the semiconductor substrate is made of silicon (Si), general bipolar transistors may be used. Moreover, although the case where all the bipolar transistors constituting the constant current circuits 100 and 101 are NPN type is illustrated, the present invention is not limited to this, and all the bipolar transistors may be PNP type. In this case, VCC <VEE.

  Further, in the constant current circuit 101 according to the second embodiment, the case where the transistor group 40 includes two bipolar transistors is illustrated, but the number of bipolar transistors in the transistor group 43 can be changed as necessary. It is. It is also possible to insert a bipolar transistor having a diode connection between the node E and the node F. In this case, if the number of bipolar transistors constituting the transistor group 43 is m and the number of bipolar transistors in the path from the node C to the second power supply VEE via the nodes E and F is n, the equation ( The coefficient of VBE in the equation 16) can be expressed by the following equation (17).

  Therefore, in this case, the values of the resistors Rb1, Rb2, Rc, Re, and m and n may be adjusted as in the following equation (18) in which the value of the equation (17) becomes zero.

  DESCRIPTION OF SYMBOLS 100, 101 ... Constant current circuit, 1, 4 ... Voltage generation circuit, 2, 5 ... Emitter follower circuit, 3 ... Current generation circuit, 10, 11, 43 ... Transistor group, 40, 41 ... Resistance voltage dividing part, 42 ... Differential amplifier circuit, VCC, VEE: power supply voltage.

Claims (3)

A first power supply line to which a first power supply voltage is supplied;
A second power supply line to which a second power supply voltage is supplied;
m (m is an integer of 1 or more) diode connected first bipolar transistor,
Connected in series to said first bipolar transistor, and n (n is an integer of 1 or more) number of diode-connected second bipolar transistor,
A first resistor connected in series with the first bipolar transistor between a node to which the first bipolar transistor and the second bipolar transistor are connected and the first power supply line;
A second resistor connected in series with the second bipolar transistor between a node to which the first bipolar transistor and the second bipolar transistor are connected and the second power supply line;
An emitter follower circuit having an input terminal connected to a node to which the first bipolar transistor and the second bipolar transistor are connected;
A third bipolar transistor having a base electrode connected to the output terminal of the emitter follower circuit;
See containing and an output resistor connected between the emitter electrode and the second power supply line of the third bipolar transistor,
A constant current circuit satisfying the following formula (A), where R1 is a resistance value of the first resistor and R2 is a resistance value of the second resistor .

The constant current circuit according to claim 1,
The emitter follower circuit is:
A fourth bipolar transistor in which current is supplied to the collector electrode from the first power supply line, and a base electrode is connected to a node to which the first bipolar transistor and the second bipolar transistor are connected;
A constant current circuit, comprising: a third resistor connected between an emitter electrode of the fourth bipolar transistor and the second power supply line. A first power supply line to which a first power supply voltage is supplied;
A second power supply line to which a second power supply voltage is supplied;
A first resistor and a second resistor connected in series between the first power line and the second power line;
A third resistor having one end connected to the second power supply line;
A first bipolar transistor connected to the other end of the third resistor and diode-connected;
A fourth resistor connected in series with the first bipolar transistor between a node to which the third resistor and the first bipolar transistor are connected and the first power supply line;
A pair of differential input terminals, wherein one of the differential input terminals is connected to a node to which the first resistor and the second resistor are connected; A differential amplifier circuit connected to a node to which the first bipolar transistor is connected;
An emitter follower circuit having an input terminal connected to the output terminal of the differential amplifier circuit;
A second bipolar transistor having a base electrode connected to an output terminal of the emitter follower circuit;
An output resistor connected between an emitter electrode of the second bipolar transistor and the second power supply line;
The differential amplifier circuit is:
A third bipolar transistor having a base electrode connected to a node to which the first resistor and the second resistor are connected;
A fourth bipolar transistor having a base electrode connected to the other end of the fourth resistor;
A fifth resistor connected between the first power supply line and a collector electrode of the third bipolar transistor;
A sixth resistor connected between the first power supply line and the collector electrode of the fourth bipolar transistor;
A seventh resistor and an eighth resistor connected in series between the emitter electrode of the third transistor and the emitter electrode of the fourth transistor;
A fifth bipolar transistor having a collector electrode connected to a node to which the seventh resistor and the eighth resistor are connected, and a base electrode connected to an output terminal of the emitter follower circuit;
A constant current circuit , comprising: a ninth resistor connected between an emitter electrode of the fifth bipolar transistor and the second power supply line .

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