Current mirror circuit and amplification circuit

Abstract

To provide a current mirror circuit in which the output current varies depending on temperature change, and an amplification circuit including the current mirror circuit.SOLUTION: Provided are: a first transistor whose first input end is connected to a first circuit with a first impedance, first output end is connected to a reference current source, and first control end is connected to the first output end; and a second transistor whose second control end is connected to the first control end, second input end is connected to a second circuit with a second impedance, and second output end outputs output current according to reference current of the reference current source. In one of or both the first circuit and the second circuit, the temperature characteristic of one of or both the first impedance and the second impedance is set so that the output current tends to change in a predetermined way for the ambient temperature.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a current mirror circuit and an amplifier circuit. [Background technology]

[0002] The following Patent Document 1 discloses a current mirror circuit. This current mirror circuit is characterized in that in a current mirror circuit in which the base of a first transistor, the base of which is connected to the collector and the emitter of which is connected to a first resistor, is connected to the base of a second transistor, the emitter of which is connected to a second resistor, and the collector of the first transistor is connected to a reference current source, a load resistor is connected to the second transistor, and the collector of the first transistor is connected to the collector of the second transistor via a capacitor. With such a current mirror circuit, the capacitance of the noise reduction capacitor can be reduced, making it easy to mount the circuit on a semiconductor substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-209446 A Summary of the Invention [Problem to be solved by the invention]

[0004] Current mirror circuits are often used to set the output bias current of an amplifier circuit. For example, the output current of the current mirror circuit is input to the drain of a bias transistor whose source is grounded, and the gate of the bias transistor is connected to the gate of an amplifier transistor via an inductor that blocks the frequency band used by the amplified signal. By adjusting the size and number ratio of the bias transistor and the amplifier transistor, the bias current flowing through the drain of the amplifier transistor can be set to a predetermined coefficient times the output current of the current mirror circuit.

[0005] Here, the bias current of the amplifying transistor is constant regardless of temperature changes, just like the output current of the current mirror circuit. In contrast, the gain of the amplifying transistor has the property of increasing at low temperatures and decreasing at high temperatures. In other words, if the bias current of the amplifying transistor is set to a constant value regardless of temperature changes, the gain of the amplifying transistor will not be constant but will fluctuate according to temperature changes.

[0006] Therefore, in order to keep the gain of the amplifying transistor constant against temperature changes, it is necessary to change the bias current of the amplifying transistor in response to temperature changes. However, changing the bias current of the amplifying transistor in response to temperature changes so that the gain of the amplifying transistor remains constant against temperature changes is problematic in that it leads to an increase in circuit size and cost.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a current mirror circuit whose output current varies in response to temperature changes, and an amplifier circuit using the current mirror circuit. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention employs, as a first solution relating to a current mirror circuit, a first transistor having a first input terminal connected to a first circuit having a first impedance and a first output terminal connected to a reference current source, and having the first output terminal connected to a first control terminal, and a second transistor having a second control terminal connected to the first control terminal and a second input terminal connected to a second circuit having a second impedance, and outputting an output current corresponding to a reference current of the reference current source from a second output terminal, wherein the temperature characteristics of either or both of the first impedance and the second impedance of either or both of the first circuit and the second circuit are set so that the output current has a predetermined tendency to change with respect to the ambient temperature.

[0009] The present invention employs a second solution related to a current mirror circuit, which is the first solution described above, in which the first impedance is set to increase with increasing temperature so that the output current has an increasing tendency with increasing ambient temperature, and the second impedance is set to decrease with increasing temperature.

[0010] The present invention employs, as a third solution relating to a current mirror circuit, a solution in which, in the first or second solution, the first circuit and the second circuit are each a single resistor.

[0011] The present invention employs, as a fourth solution related to a current mirror circuit, a solution in which, in the first or second solution described above, the first circuit and the second circuit are resistance circuits in which a plurality of resistors are connected in series, in parallel, or in series and in parallel.

[0012] The present invention employs, as a fifth solution related to a current mirror circuit, any one of the first to fourth solutions, in which the first transistor and the second transistor are p-type MOS transistors.

[0013] The present invention employs, as a solution relating to an amplifier circuit, a solution in which a current mirror circuit relating to any one of the above first to fifth solutions is provided as a bias circuit that sets an output bias current. Effect of the Invention

[0014] According to the present invention, it is possible to provide a current mirror circuit whose output current varies in response to temperature changes, and an amplifier circuit using the current mirror circuit. [Brief description of the drawings]

[0015] [Figure 1] 1 is a circuit diagram showing configurations of an amplifier circuit A and a current mirror circuit B according to an embodiment of the present invention. [Diagram 2]4A is a characteristic diagram showing the temperature dependence of a first resistance value R1 and a second resistance value R2 in one embodiment of the present invention, and FIG. 4B is a characteristic diagram showing the temperature dependence of a reference current Iref and an output current Iout in one embodiment of the present invention. [Diagram 3] 4A is a characteristic diagram showing the temperature characteristics of an output current Iout and an output bias current Iamp in one embodiment of the present invention, and FIG. 4B is a characteristic diagram showing the temperature characteristics of a gain of an amplifier circuit A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The amplifier circuit A according to this embodiment is a high-frequency amplifier circuit that amplifies a high-frequency signal input from the outside, and includes a current mirror circuit B and an amplifier section C, as shown in Fig. 1. That is, the amplifier circuit A according to this embodiment includes the current mirror circuit B as a bias circuit that sets the output bias current of the amplifier section C.

[0017] As shown in the figure, the current mirror circuit B includes a first transistor 1, a first resistor 2, a reference current source 3, a second transistor 4, and a second resistor 5. Also, as shown in the figure, the amplifier section C includes a third transistor 6, an inductor 7, a fourth transistor 8, a third resistor 9, an input terminal Tin, and an output terminal Tout.

[0018] In the current mirror circuit B, the first transistor 1 is a p-type MOS (Metal Oxide Semiconductor) transistor as shown in the figure. The source terminal of this first transistor 1 is connected to one end of the first resistor 2, and the drain terminal is connected to the input terminal of the reference current source 3, its own gate terminal, and the gate terminal of the second transistor 4.

[0019] Moreover, the gate terminal of this first transistor 1 is connected to its own drain terminal, the input terminal of the reference current source 3, and the gate terminal of the second transistor 4. In the first transistor 1, the source terminal corresponds to the first input terminal in the present invention, the drain terminal corresponds to the first output terminal in the present invention, and the gate terminal corresponds to the first control terminal in the present invention.

[0020] The first resistor 2 has a predetermined first resistance value R1(Tj). That is, the first resistor 2 has a first resistance value R1(Tj) that changes according to the ambient temperature Tj. One end of the first resistor 2 is connected to the source terminal of the first transistor 1, and the other end is connected to a power supply.

[0021] The first resistance value R1(Tj) corresponds to the first impedance of the present invention, and its temperature characteristics are set so that the output current Iout of the current mirror circuit B has a predetermined tendency to change with respect to the ambient temperature Tj. Such a first resistor 2 corresponds to the first circuit of the present invention.

[0022] Although details will be described later, the first resistance value R1(Tj) is set, for example, so that the gain of the amplifier section C is approximately constant with respect to changes in ambient temperature. In a normal current mirror circuit, a resistor whose resistance value does not depend on temperature is used, but in the current mirror circuit B according to this embodiment, a first resistor 2 having a first resistance value R1(Tj) with temperature dependency such that the gain of the amplifier section C does not fluctuate with changes in the ambient temperature Tj is used.

[0023] The reference current source 3 has an input terminal connected to the drain terminal and gate terminal of the first transistor 1 and the gate terminal of the second transistor 4, and an output terminal grounded. This reference current source 3 flows a predetermined reference current Iref from the input terminal to the output terminal. This reference current Iref is the operating reference current of the current mirror circuit B, and governs the output current Iout of the current mirror circuit B.

[0024] The second transistor 4 is a p-type MOS (Metal Oxide Semiconductor) transistor as shown in the drawing. The source terminal of the second transistor 4 is connected to one end of the second resistor 5, and the drain terminal is connected to the drain terminal and gate terminal of the third transistor 6 and one end of the inductor 7.

[0025] Moreover, the gate terminal of this second transistor 4 is connected to the drain terminal and gate terminal of the first transistor 1 and the input terminal of the reference current source 3. The element size of this second transistor 4 is the same as that of the first transistor 1. Moreover, in the second transistor 4, the source terminal corresponds to the second input terminal in the present invention, the drain terminal corresponds to the second output terminal in the present invention, and the gate terminal corresponds to the second control terminal in the present invention.

[0026] The second resistor 5 has a predetermined second resistance value R2. That is, the second resistor 5 has a second resistance value R2(Tj) that changes according to the ambient temperature Tj. One end of the second resistor 5 is connected to the source terminal of the second transistor 4, and the other end is connected to the power supply.

[0027] The second resistance value R2 corresponds to the second impedance of the present invention, and has a temperature characteristic set so that the output current Iout of the current mirror circuit B has a predetermined tendency to change with respect to the ambient temperature Tj, similar to the first resistance value R1(Tj) of the first resistor 2. Such a second resistor 5 corresponds to the second circuit of the present invention.

[0028] Although details will be described later, the second resistance value R2(Tj) is set, for example, so that the gain of the amplifier section C is approximately constant with respect to changes in ambient temperature. As described above, in a normal current mirror circuit, a resistor whose resistance value does not depend on temperature is used, but in the current mirror circuit B according to this embodiment, the second resistor 5 having the second resistance value R2(Tj) with temperature characteristics such that the gain of the amplifier section C does not fluctuate with changes in the ambient temperature Tj is used.

[0029] As shown in the figure, the third transistor 6 is an n-type MOS (Metal Oxide Semiconductor) transistor. The drain terminal of this third transistor 6 is connected to its own gate terminal, the drain terminal of the second transistor 4, and one end of the inductor 7, and the source terminal is grounded. In addition, the gate terminal of this third transistor 6 is connected to its own drain terminal, the drain terminal of the second transistor 4, and one end of the inductor 7.

[0030] The inductor 7 has a predetermined inductance, one end of which is connected to the gate terminal and drain terminal of the third transistor 6 and the drain terminal of the second transistor 4, and the other end of which is connected to the input terminal Tin and the gate terminal of the fourth transistor 8. This inductor 7 functions as a low-pass filter that passes a direct current but blocks a high-frequency signal (input AC signal) input from the outside to the input terminal Tin from being input to the second transistor 4 and the third transistor 6. This inductor 7 is formed of, for example, a coil (winding) or a long line.

[0031] As shown in the figure, the fourth transistor 8 is an n-type MOS (Metal Oxide Semiconductor) transistor. The gate terminal of this fourth transistor 8 is connected to the input terminal Tin and the other end of the inductor 7, and the source terminal is grounded. In addition, the drain terminal of this fourth transistor 8 is connected to one end of the third resistor 9 and the output terminal Tout. The element size of this fourth transistor 8 is the same as that of the third transistor 6.

[0032] The fourth transistor 8 is an amplifying transistor that amplifies a high-frequency signal input from the outside to the input terminal Tin. As can be seen from the fact that the gate terminal and the drain terminal of the third transistor 6 are interconnected, the fourth transistor 8, the third transistor 6 and the inductor 7 form a second current mirror circuit.

[0033] That is, the third transistor 6, the inductor 7, and the fourth transistor 8 configure a second current mirror circuit that uses the output current Iout of the current mirror circuit B as an operating reference current. Therefore, the output bias current Iamp of the fourth transistor 8 is set based on the output current Iout of the current mirror circuit B.

[0034] The third resistor 9 has a predetermined third resistance value, one end of which is connected to the drain terminal of the fourth transistor 8 and the output terminal Tout, and the other end of which is connected to the power supply. The third resistor 9 is a load resistor of the fourth transistor 8. That is, the third resistance value contributes to the gain of the amplifier circuit A.

[0035] The input terminal Tin is connected to the other end of the inductor 7 and the gate terminal of the fourth transistor 8 inside the amplifier unit C. In addition, this input terminal Tin is connected to a predetermined signal supply source outside the amplifier unit C. A high-frequency signal is input to this input terminal Tin from the external signal supply source as an input AC signal.

[0036] The output terminal Tout is connected to the drain terminal of the fourth transistor 8 and one end of the third resistor 9 inside the amplifier section C. In addition, this output terminal Tout is connected to a predetermined subsequent circuit outside the amplifier section C. In other words, the output terminal Tout outputs a signal (high frequency signal) obtained by amplifying a high frequency signal (input AC signal) by the amplifier circuit A to the external subsequent circuit.

[0037] Next, the operations of the amplifier circuit A and the current mirror circuit B according to this embodiment will be described in detail with reference to FIGS.

[0038] First, the first resistance R1(Tj) and the second resistance R2(Tj) in the current mirror circuit B have the temperature dependency (temperature characteristic) shown in Fig. 2(a) with respect to the change in the ambient temperature Tj. That is, the first resistance R1 has a temperature characteristic of increasing linearly as the ambient temperature Tj increases. In contrast, the second resistance R2(Tj) has a temperature characteristic of decreasing linearly as the ambient temperature Tj increases.

[0039] Due to the first resistance value R1(Tj) and the second resistance value R2(Tj), the output current Iout of the current mirror circuit B has the temperature dependency (temperature characteristic) shown in Fig. 2(b). That is, although the reference current Iref does not have temperature dependency, the output current Iout has a temperature characteristic that increases linearly as the ambient temperature Tj rises.

[0040] Looking at the current mirror circuit B, the reference current Iref flows through the first transistor 1, so a gate-source voltage Vgs(Iref) is generated in the first transistor 1. In addition, the reference current Iref also flows through the first resistor 2, so a voltage drop is generated in the first resistor 2, which is the reference current Iref multiplied by the first resistance value R1(Tj).

[0041] On the other hand, since the output current Iout flows through the second transistor 4, a gate-source voltage Vgs(Iout) is generated in the second transistor 4. In addition, since the output current Iout also flows through the second resistor 5, a voltage drop is generated in the second resistor 5, which is the output current Iout multiplied by the second resistance value R2(Tj).

[0042] Therefore, the relationship of the following formula (1) is established among the first resistance value R1(Tj), the second resistance value R2(Tj), the reference current Iref, and the output current Iout in the current mirror circuit B. Vgs(Iref)+Iref×R1(Tj) = Vgs(Iout) + Iout × R2(Tj) (1)

[0043] Here, since the difference between the gate-source voltage Vgs(Iref) of the first transistor 1 and the gate-source voltage Vgs(Iout) of the second transistor 4 is small, equation (1) can be transformed into the following equation (2). Iref×R1(Tj)=Iout×R2(Tj) (2)

[0044] When the first resistor 2 and the second resistor 5 having the first resistance value R1(Tj) and the second resistance value R2(Tj) as shown in Fig. 2(a) are adopted, since the relationship R1(Tj)>R2(Tj) is satisfied at a relatively high ambient temperature Tj, Iref<Iout according to Equation (2). As a result, at a relatively high ambient temperature Tj, the output current Iout becomes larger than the reference current Iref.

[0045] On the other hand, at a relatively low ambient temperature Tj, since the relationship R1(Tj)<R2(Tj) is satisfied, Iref>Iout according to Equation (2). As a result, at a relatively low ambient temperature Tj, the output current Iout becomes smaller than the reference current Iref.

[0046] Therefore, even when the reference current Iref is constant, since the first resistance value R1(Tj) and the second resistance value R2(Tj) have temperature characteristics as shown in Fig. 2(a) in the current mirror circuit B according to the present embodiment, as the ambient temperature Tj rises as shown in Fig. 2(b), the output current Iout increases linearly.

[0047] Since the amplifier circuit A according to the present embodiment includes such a current mirror circuit B as a bias circuit for setting the output bias current Iamp of the amplifier section C (the fourth transistor 8), as shown in Fig. 3(a), as the ambient temperature Tj rises, the output bias current Iamp of the fourth transistor 8 increases linearly.

[0048] Here, as is well known as the element performance of an n-type MOS (Metal Oxide Semiconductor) transistor, the fourth transistor 8 has a characteristic (gain characteristic) in which the gain decreases linearly as the ambient temperature Tj rises.

[0049] With respect to such gain characteristics, since the output bias current Iamp of the fourth transistor 8 increases as the ambient temperature Tj rises in the amplifier circuit A according to the present embodiment, a decrease in gain due to an increase in the ambient temperature Tj can be suppressed, and fluctuations in gain can be suppressed even when the ambient temperature Tj changes as shown in Fig. 3(b).

[0050] That is, according to this embodiment, by selecting the first resistor 2 and the second resistor 5 of the current mirror circuit B so as to keep the gain of the amplifier section C constant, it is possible to suppress fluctuations in the gain of the amplifier section C even if the ambient temperature Tj changes.

[0051] According to this embodiment, it is possible to provide an amplifier circuit A and a current mirror circuit B in which the output current Iout varies in response to changes in the ambient temperature Tj. Also, according to this embodiment, since the current mirror circuit B is provided as a bias circuit, it is possible to provide an amplifier circuit A capable of suppressing fluctuations in gain even if the ambient temperature Tj varies.

[0052] The present invention is not limited to the above-described embodiment, and the following modifications are possible. (1) In the above embodiment, the output bias current Iamp of the fourth transistor 8 is linearly increased with an increase in the ambient temperature Tj, but the present invention is not limited to this. For example, if the fourth transistor 8 has a characteristic that the gain increases linearly with an increase in the ambient temperature Tj, one or both of the first impedance and the second impedance may be set so that the output bias current Iamp decreases linearly with an increase in the ambient temperature Tj.

[0053] (2) In the above embodiment, a single first resistor 2 is used as the first circuit, and a single second resistor 5 is used as the second circuit, but the present invention is not limited to this. For example, a resistance circuit in which a plurality of resistors are connected in series, in parallel, or in series and in parallel may be used as the first circuit and the second circuit.

[0054] (3) In the above embodiment, resistors whose resistance values ​​change when the ambient temperature Tj changes are used for both the first resistor 2 and the second resistor 5, but the present invention is not limited to this. That is, it is sufficient that either one of the first resistor 2 and the second resistor 5 has temperature characteristics that can suppress fluctuations in the gain of the amplifier section C.

[0055] (4) In the above embodiment, p-type MOS (Metal Oxide Semiconductor) transistors are used for the first transistor 1 and the second transistor 4, and n-type MOS (Metal Oxide Semiconductor) transistors are used for the third transistor 6 and the fourth transistor 8, but the present invention is not limited to this. For example, PNP-type bipolar transistors may be used for the first transistor 1 and the second transistor 4, and NPN-type bipolar transistors may be used for the third transistor 6 and the fourth transistor 8.

[0056] (5) In the above embodiment, a common-source amplifier circuit using the fourth transistor 8 is used as the amplifier section C. However, the present invention is not limited to this. Various configurations of the amplifier circuit in the amplifier section C can be used.

[0057] (6) In the above embodiment, the drain terminal and gate terminal of the first transistor 1 are directly connected, and the drain terminal and gate terminal of the third transistor 6 are directly connected, but the present invention is not limited to this. The drain terminal and gate terminal of the first transistor 1 may be interconnected using a separately provided p-type MOS transistor (first additional transistor). Also, the drain terminal and gate terminal of the third transistor 6 may be interconnected using a separately provided n-type MOS transistor (second additional transistor).

[0058] That is, the first additional transistor has a gate terminal connected to the drain terminal of the first transistor 1, a source terminal connected to the gate terminal of the first transistor 1, and a drain terminal grounded. Also, the second additional transistor has a gate terminal connected to the drain terminal of the third transistor 6, a source terminal connected to the gate terminal of the third transistor 6, and a drain terminal connected to the power supply. [Explanation of symbols]

[0059] A Amplification circuit, B Current mirror circuit, C Amplifier section, Tin Input terminal, Tout Output terminal, 1 First transistor, 2 First resistor, 3 Reference current source, 4 Second transistor, 5 Second resistor, 6 Third transistor, 7 Inductor, 8 Fourth transistor, 9 Third resistor

Claims

1. a first transistor having a first input terminal connected to a first circuit having a first impedance, a first output terminal connected to a reference current source, and a first control terminal connected to the first output terminal; a second transistor having a second control terminal connected to the first control terminal and a second circuit having a second impedance connected to a second input terminal, and outputting an output current from a second output terminal according to a reference current of the reference current source, A current mirror circuit characterized in that either or both of the first circuit and the second circuit have temperature characteristics of either or both of the first impedance and the second impedance set so that the output current has a predetermined tendency to change with respect to the ambient temperature.

2. the first impedance is set to increase with increasing temperature such that the output current has an increasing tendency with increasing ambient temperature; 2. The current mirror circuit according to claim 1, wherein the second impedance is set so as to decrease with increasing temperature.

3. 3. The current mirror circuit according to claim 1, wherein the first circuit and the second circuit are each a single resistor.

4. 3. The current mirror circuit according to claim 1, wherein the first circuit and the second circuit are resistance circuits in which a plurality of resistors are connected in series, in parallel, or in series and in parallel.

5. 3. The current mirror circuit according to claim 1, wherein the first transistor and the second transistor are p-type MOS transistors.

6. 3. An amplifier circuit comprising the current mirror circuit according to claim 1 or 2 as a bias circuit for setting an output bias current.

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