JP2000077955A - Ab class amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use an AB class amplifier with low voltage, e.g. <=2 V. SOLUTION: A mirror transistor 202 to a transistor 201 for current sink is provided and the mirror transistor 202 controls a transistor 205 for a current source. When a collector current of the transistor 202 increases, almost all of the collector current of the transistor 201 is fed by a sink current extracted from an output side because the collector current of the transistor 202 increases but the collector current of the transistor 205 reduces. On the other hand, when the collector current of the transistor 202 reduces, almost all of the collector current of the transistor 205 is caused to flow toward the output side to be a source current because the collector current of the transistor 201 reduces but the collector current of the transistor 205 increases. Then, an output dynamic range becomes Vsat to (Vcc to Vsat) and is available with <=2 V.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier (operational amplifier), and more particularly, to a low-voltage class AB amplifier constituted by transistors built in an IC (integrated circuit).

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram showing a configuration of a conventional class A amplifier. Here, the class A amplifier is an amplifier having a configuration in which a resistor or a constant current source is connected to the upper side of the output stage and connected to a transistor capable of moving the collector current in the lower side, or an amplifier having the opposite configuration. is there. The class A amplifier shown in FIG. 7 includes a differential amplifier 101, two NPN transistors 102 and 104, a power supply 103, and a constant current source 1
05.

[0003] The differential amplifier 101 has an output terminal connected to the base terminal of the transistor 102 and drives the transistor 102. The transistor 102 has a collector terminal and an emitter terminal connected to a power source 103, respectively.
And the base terminal of the transistor 104 to drive the transistor 104. Transistor 10
4 is connected to the other end of the constant current source 105 having one end connected to the power supply 103 and the output end (OU
T), and the emitter terminal of the transistor 104 is grounded. This transistor 104
Controls the amount of current drawn from the output end of the amplifier. An output terminal of the amplifier is supplied with an output current from a constant current source 105.

A current supplied from the output terminal of the amplifier to the outside (hereinafter referred to as a source current) is a transistor 10
4 is zero when the collector current is zero, and the current value at that time is equal to the maximum value of the current capability of the constant current source 105. The maximum value of a current (hereinafter, referred to as a sink current) drawn from the outside via the output terminal of the amplifier is determined by the transistor 10
4 is a value obtained by subtracting the current value of the constant current source 105 from the maximum capability value of the collector current of No. 4. In order to improve switching characteristics and crossover distortion at the time of switching between the sink mode and the source mode, a through current flowing between the power supply 103 and the ground point, that is, an idling current is controlled by a constant current source 105.
Is the same as the current flowing.

When the constant current source 105 is constituted by a PNP transistor, the output dynamic range is the minimum voltage between the emitter and the collector of the transistor 104, that is, the saturation voltage of the transistor 104 (hereinafter, the saturation voltage is represented by Vsat
PNP that constitutes the constant current source 105
The voltage is lower than the power supply voltage (hereinafter, the power supply voltage is referred to as Vcc) by Vsat of the transistor. Assuming that Vsat of the transistor 104 and the PNP transistor as the constant current source 105 are each 0.3 V and Vcc is 5 V, the output dynamic range of this class A amplifier is 0.3 V to 4.7 V.

However, in the class A amplifier, the upper current supply source is the constant current source 105, and the transistor 104 constantly draws a current unnecessary for output.
Of the current flowing through the amplifier 05, the current that does not go to the outside of the amplifier as the output of the amplifier always flows as a through current from the power supply 103 to the ground point, and thus has a problem that the current efficiency is poor. If the current efficiency is poor, energy loss increases, and problems such as an increase in power consumption and an unintended increase in the amount of heat generation occur. This is particularly unsuitable for battery-powered portable electronic devices that require low power consumption. Further, the sink current capability of the amplifier is smaller than the current capability of the transistor 104 by the constant current from the constant current source 105.

In order to solve the problem of the reactive current of the class A amplifier, there is a class AB amplifier called a push-pull type amplifier.

FIG. 8 is a circuit diagram showing a configuration of a conventional class AB amplifier. Here, the class AB amplifier is an amplifier having a configuration in which both the upper and lower sides of the output stage are connected to a transistor having a movable emitter current, and through which a slight through current flows. Class AB amplifier
A class B amplifier in which the lower transistor is turned off when the upper transistor is turned on and the upper transistor is turned off when the lower transistor is turned on, thereby preventing a through current from flowing from the power supply to the ground point. Switching characteristics have been improved. The class AB amplifier shown in FIG.
A differential amplifier 108, three NPN transistors 109,
111, 115, PNP transistor 116, power supply 11
0, constant current source 112 and two diodes 113, 1
14.

The output terminal of the differential amplifier 108 is connected to the base terminal of the transistor 109, and drives the transistor 109. Transistor 109 has a collector terminal and an emitter terminal connected to power supply 110, respectively.
And a base terminal of the transistor 111 to drive the transistor 111. Transistor 11
One collector terminal is connected to the anode of the diode 114 and the base of the transistor 116, and the emitter terminal of the transistor 111 is grounded.
The cathode of the diode 114 is connected to the anode of the diode 113, and the cathode of the diode 113 is connected to a constant current source 112 having one end connected to the power supply 110.
And the base of the transistor 115. Transistor 115 and transistor 116 are commonly connected to the output terminal (OUT) of the amplifier, and the collector of transistor 115 and transistor 1
The 16 collectors are connected to a power supply 110 and a ground point, respectively.

The current value of the constant current source 112 is represented by Ic
, The collector current of the transistor 111 is Id, the beta amplification factor of the transistor 115 is BF1, and the transistor 1 is
The beta gain of 16 is BF2 and the diode 11
When the current ratio determined by the emitter size ratio between the transistors 3,114 and the transistors 115,116 is represented by K, the source current Iso, the sink current Isi, and the idling current Iid of the class AB amplifier are expressed by the following equations (1) and (2), respectively. )formula,
Determined by equation (3).

Iso = (Ic−Id) · BF1 (1) Isi = (Id−Ic) · BF2 (2) Iid = Ic · K (3)

The output dynamic range is determined by the constant current source 11
2 is composed of a PNP transistor, the voltage between the base and the emitter of the transistor 116 (hereinafter, the voltage between the base and the emitter is represented by Vbe) and the voltage Vsa of the transistor 111
t and the voltage of the transistor 115
be and V of the PNP transistor forming the constant current source 112
The voltage is lower than Vcc by a voltage obtained by adding sat. If Vsat and Vbe are 0.3 V and 0.7 V, respectively, and Vcc is 5 V, the output dynamic range of this class AB amplifier is 1.0 V to 4.0 V.

FIG. 9 shows a conventional class A amplifier (FIGS.
For each of (c)) and the push-pull type class AB amplifier (FIGS. (D) to (f)), the relationship between the input voltage, the output voltage, and the through current is shown for the case where a voltage follower with a voltage gain of 1 is formed. Show.

[0014]

However, the conventional A
In the class B amplifier, as described above, the lowest potential of the output dynamic range is the sum of Vbe and Vsat (Vbe + Vsat), and the highest potential is the potential obtained by subtracting the sum of Vbe and Vsat from Vcc (Vcc- (Vbe + Vsat)). Therefore, there is a disadvantage that the output dynamic range is narrowed by 2 Vbe, for example, about 1.4 V as compared with the class A amplifier, and therefore, there is a problem that the output does not operate at an output of 2 V or less.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended to solve the above problems.
The purpose is to obtain a class amplifier.

[0016]

In order to achieve the above object, the present invention provides a transistor for a current source for flowing a current toward an output side, and a transistor for a current sink for extracting a current from the output side. A constant current source for flowing a current capable of driving the transistor for the current source;
Of the currents flowed by the constant current source, while controlling the amount of current flowing to the current source transistor side to drive the current source transistor,
A mirror transistor through which a current corresponding to a current flowing through the current sink transistor flows, and a fourth transistor controlling driving of the current sink transistor and driving of the mirror transistor in accordance with an external input; When the current flowing through the mirror transistor increases due to the fourth transistor,
The current flowing through the current sinking transistor increases, and the driving current of the current source transistor decreases, so that the current flowing through the current source transistor decreases. When the current flowing through the transistor decreases, the current flowing through the current sink transistor decreases, and the driving current of the current source transistor increases, and the current flowing through the current source transistor increases. I have.

According to the present invention, since the current source transistor is controlled by the mirror transistor for the current sink transistor, the sink current and the source current are respectively the current flowing through the current sink transistor and the current source. Current flowing through the transistor.

Further, according to the present invention, a transistor for a current source for flowing a current toward an output side, a transistor for a current sink for extracting a current from the output side, and a transistor for the current sink can be driven. A constant current source for flowing a current, of the current flowing by the constant current source,
Controlling the amount of current flowing from the current sink transistor side to drive the current sink transistor, a mirror transistor through which a current corresponding to the current flowing through the current source transistor flows, and an external input And a fourth transistor that controls the driving of the current source transistor and the driving of the mirror transistor, the current flowing through the mirror transistor being increased by the fourth transistor. The current flowing through the source transistor increases, and the drive current of the current sink transistor decreases to reduce the current flowing through the current sink transistor. On the other hand, the mirror transistor is controlled by the fourth transistor. When the flowing current decreases, the current source Decreased current through the transistor, and the current flowing through the transistor for the current sink drive current increases of the transistor for the current sink is adapted to increase.

According to the present invention, since the current sink transistor is controlled by the mirror transistor for the current source transistor, the sink current and the source current are respectively the current flowing through the current sink transistor and the current source. Current flowing through the transistor.

In these inventions, the current source transistor may be a PNP bipolar transistor, and the current sink transistor may be an NPN bipolar transistor.

According to the present invention, the sink current and the source current are respectively the collector current of the NPN type bipolar transistor for current sink and the PNP for current source.
It becomes the collector current of the bipolar transistor.

In these inventions, a resistor for suppressing the saturation of the mirror transistor may be connected between the base terminal of the mirror transistor and the emitter terminal of the fourth transistor.

According to the present invention, since the resistor for suppressing the saturation of the mirror transistor is provided, the saturation of the mirror transistor when the collector current of the mirror transistor needs to flow more is suppressed. You.

In these inventions, a capacitor for phase compensation may be connected between the input of the fourth transistor and the output of the class AB amplifier.

According to the present invention, since the phase compensating capacitor is provided, the phase compensating effect when the class AB amplifier operates is large.

In these inventions, each of the transistors may be a MOS transistor.

According to the present invention, even when MOS transistors are used, the sink current and the source current are the current flowing through the current sink transistor and the current flowing through the current source transistor, respectively.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a circuit diagram showing a configuration of the class AB amplifier according to the first embodiment of the present invention. This class AB amplifier is, for example, a differential amplifier 20.
6, three NPN transistors 201, 202, 20
3, PNP transistor 205, resistor 204, power supply 20
9, a constant current source 207 and a current amplification stage 208.

The output terminal of the differential amplifier 206 is connected to the base terminal of the transistor 203, and drives the transistor 203.

The transistor 203 has a collector terminal connected to the power supply 209 and an emitter terminal connected to the base terminal of the transistor 201, and drives the transistor 201. The emitter terminal of the transistor 203 is connected to one end of the resistor 204, and the other end of the resistor 204 is connected to the base terminal of the transistor 202. Therefore, the transistor 203 also drives the transistor 202.

The collector terminal of the transistor 201 and the collector terminal of the transistor 205 are commonly connected to the output terminal of this amplifier, and the emitter terminal of the transistor 201 is grounded. The transistor 201 is a current sink transistor.

The emitter terminal and the base terminal of the transistor 205 are connected to the power supply 209 and the current amplification stage 2 respectively.
08 is connected to the output terminal. Transistor 205
Is a current source transistor.

The current amplification stage 208 includes a transistor 205
And a current amplifier that amplifies the current.

The collector terminal of the transistor 202 is connected to the other end of the constant current source 207 whose one end is connected to the power supply 209 and to the input terminal of the current amplification stage 208, and the emitter terminal of the transistor 202 is grounded. . The transistors 201 and 202 form a current mirror circuit, and the transistor 202 is a mirror transistor of the transistor 201 for current sink. The mirror transistor 202 controls a current source transistor 205.

Next, the operation of the first embodiment will be described. The current gain of the block indicated by the broken line in FIG.
01, the current ratio of a current mirror formed by the transistor 202 is B, the current value of the constant current source 207 is Io,
When the collector current of the transistor 202 is represented by I1, the output current Iout of the class AB amplifier is a composite of the collector current (A. (Io -I1)) of the transistor 205 and the collector current (B.I1) of the transistor 201. It is determined by the minute and is expressed by the following equation (4). Iout = A · (Io−I1) −B · I1 = A · Io− (A + B) · I1 (4)

When the class AB amplifier requires a large source current, the differential amplifier 206
To reduce the current supplied to the base of transistor 202, thereby reducing the base current supplied to transistor 202, thereby decreasing the collector current I1 of transistor 202. When the collector current I1 of the transistor 202 decreases, the current (Io) flowing into the current amplification block shown by the broken line in FIG.
−I1) increases, so that the collector current (A · (Io−I1)) of the transistor 205 increases. At this time, the base current of the transistor 201 also decreases, so that the collector current (B · I1) of the transistor 201 also decreases.
The current flowing through 01 to ground is reduced and most of the collector current of transistor 205 flows toward the output of this class AB amplifier. That is, the source current of the class AB amplifier increases.

The output current at the time of current source becomes maximum when the collector current I1 of the transistor 202 is zero (I1 = 0), and the output current Iout at that time is the transistor 20
5 is equal to the collector current (A · Io). That is, the following equation is obtained. Iout = A · Io

On the other hand, when the class AB amplifier requires a large amount of sink current, the differential amplifier 206 acts to increase the current supplied to the base of the transistor 203. Accordingly, the emitter current of the transistor 203 increases, so that the base current of the transistor 201 increases, and therefore, the collector current (B · I1) of the transistor 201 increases. At this time, the base current of the transistor 202 increases, so that the collector current I
Since 1 increases, the current (Io-I1) flowing into the current amplification block indicated by the broken line in FIG. 1 and including the transistor 205 and the current amplification stage 208 decreases. Accordingly, the collector current (A. (Io-I1)) of the transistor 205 decreases, and the current flowing from the power supply 209 via the transistor 205 out of the collector current of the transistor 201 decreases, and the collector current (B.I
Most of 1) flows from the output of this class AB amplifier.
That is, the sink current of the class AB amplifier increases.

The output current at the time of current sinking is such that when I1 is equal to Io (I1 = Io), the collector current of the transistor 205 becomes zero, and the output current Iout at that time becomes equal to the collector current (-B.I1) of the transistor 201. Become equal. That is, the following equation is obtained. Iout = −B · I1 = −B · Io

When more sink current is required, a current is supplied from the emitter of the transistor 203 to the base of the transistor 201, so that a current corresponding to the current capability of the transistor 201 is generated from the output of the class AB amplifier. Can be pulled in. At this time, the saturation of the transistor 202 is suppressed by the resistor 204.
The idling current Iid at the time of no load is the current (B ・) when Iout is set to zero (Iout = 0) in the above equation (4).
I1) and is expressed by the following equation (5). Iid = (A · B / (A + B)) · Io (5) The idling current at no load is a PNP transistor for a current source when no load is applied in the above equation (4), that is, when Io = 0. Or the collector current of the current sinking NPN transistor (both have the same value). Therefore, the above equation (5) can be derived by calculating I1 from equation (4) and multiplying by B.

FIG. 2 shows the relationship among the input voltage, the output voltage, and the through current (idling current) when the class AB amplifier forms a voltage follower with an input gain of 1.

According to the first embodiment, the sink current and the source current are the collector currents of the NPN transistor 201 for current sink and the PNP transistor 205 for current source, respectively, and the mirror transistor of the transistor 201 for current sink. Since the current source transistor 205 is controlled by 202,
The output dynamic range of the class AB amplifier is equal to or higher than Vsat of the transistor 201 and is equal to or higher than Vsat of the transistor 201, similarly to the conventional class A amplifier (see FIG. 9B).
The voltage is lower than the voltage (Vcc-Vsat) lower by Vsat of 05 (see FIG. 2B). For example, transistor 20
Assuming that Vsat of 1,205 is 0.3 V and Vcc is 5 V, the output dynamic range of this class AB amplifier is 0.3 V to 4.7 V.

According to the first embodiment, the reactive current at the time of current source and current sink is small, the value of the reactive current does not exceed the value determined by the above equation (5), and the switching characteristics and the Since the idling current that affects over-distortion and the like is determined only by A, B, and Io in equation (5), stabilization is easy.

Furthermore, according to the first embodiment, since it can be used with a low power supply voltage and consumes low power,
It can be used as an analog amplifier in a ~ 5V power supply system, and is particularly suitable for a system such as a portable electronic device using a battery as a power supply.

Embodiment 2 FIG. 3 is a circuit diagram showing a configuration of the class AB amplifier according to the second embodiment of the present invention.
The class AB amplifier includes, for example, a differential amplifier 1206, three PNP transistors 1201, 1202, 1203,
NPN transistor 1205, resistor 1204, power supply 12
09, a constant current source 1207 and a current amplification stage 1208.

The output terminal of the differential amplifier 1206 is connected to the base terminal of the transistor 1203, and drives the transistor 1203.

Transistor 1203 has its collector terminal grounded and its emitter terminal connected to transistor 1
201 is connected to the base terminal of
201 is driven. The emitter terminal of the transistor 1203 is connected to one end of the resistor 1204, and the other end of the resistor 1204 is connected to the base terminal of the transistor 1202. Therefore, the transistor 1203 also drives the transistor 1202.

The collector terminal of the transistor 1201 is
The collector terminal of the transistor 1205 and the output terminal of this amplifier are commonly connected together.
One emitter terminal is connected to a power supply 1209. The transistor 1201 is a transistor for a current source.

The emitter terminal and the base terminal of the transistor 1205 are connected to the ground point and the current amplifying stage 12 respectively.
08 is connected to the input terminal. Transistor 120
5 is a transistor for current sink.

The current amplification stage 1208 includes the transistor 12
05 is a current amplifier that amplifies the current together with the current.

The collector terminal of the transistor 1202 is
One end is connected to the other end of the grounded constant current source 1207 and the output terminal of the current amplification stage 1208, and the emitter terminal of the transistor 1202 is connected to the power supply 1209. The transistors 1201 and 1202 constitute a current mirror circuit, and the transistor 1202 is a mirror transistor of the transistor 1201 for current source. And this mirror transistor 1202
Controls the transistor 1205 for current sink.

Next, the operation of the second embodiment will be described. The current gain of the block indicated by the broken line in FIG. 3 including the transistor 1205 and the current amplification stage 1208 is A, the current ratio of the current mirror formed by the transistors 1201 and 1202 is B, and the current value of the constant current source 1207 is Denoting Io and the collector current of the transistor 1202 by I1, the output current Iout of this class AB amplifier
Is the collector current of transistor 1201 (B · I1)
And the collector current (A · (Io −
I1)), and is determined by the following equation (6). Iout = B · I1−A · (Io−I1) = (A + B) · I1−A · Io (6)

When the class AB amplifier requires a large amount of source current, the differential amplifier 1206 includes the transistor 12
03 acts to increase the base current. Accordingly, the emitter current of the transistor 1203 increases, so that the base current of the transistor 1201 increases, and therefore, the collector current (B · I1) of the transistor 1201 increases. At this time, the base current of the transistor 1202 increases, so that the collector current I1 of the transistor 1202 increases.
Increases, the current (Io-I1) drawn from the current amplification block indicated by the broken line in FIG. 3 including the transistor 1205 and the current amplification stage 1208 decreases. Therefore, the collector current of the transistor 1205 (A. (Io -I1
)), The current flowing to the ground via the transistor 1205 out of the collector current of the transistor 1201 decreases, and most of the collector current (B · I1) of the transistor 1201 goes to the output of the class AB amplifier. Flowing. That is, the source current of the class AB amplifier increases.

The output current at the time of current source is such that when I1 is equal to Io (I1 = Io), the collector current of the transistor 1205 becomes zero, and the output current Iout at that time is equal to the collector current (BＢI1) of the transistor 1201. Become. That is, the following equation is obtained. Iout = B · I1 = B · Io

When more source current is required, the emitter current of the transistor 1203 increases, so that the current increases at the base of the transistor 1201 and the current corresponding to the current capability of the transistor 1201 is increased by the output of the class AB amplifier. Flows towards At that time, resistance 12
04 suppresses the saturation of the transistor 1202.

On the other hand, when the class AB amplifier requires a large sink current, the differential amplifier 1206 acts to reduce the base current of the transistor 1203, thereby reducing the base current of the transistor 1202.
The collector current I1 of the transistor 1202 decreases.
When the collector current I1 of the transistor 1202 decreases, the current (Io-I1) drawn from the current amplification block indicated by the broken line in FIG. 3 including the transistor 1205 and the current amplification stage 1208 increases, so that the collector current (A. (Io) -I1)) increases. At that time, the base current of the transistor 1201 also decreases, so that the collector current (B · I1) of the transistor 1201 also decreases. Therefore, the current flowing from the power supply 1209 through the transistor 1201 out of the collector current of the transistor 1205 decreases, and the transistor 1205 Of the collector current flows from the output of the class AB amplifier. That is, the sink current of the class AB amplifier increases.

The output current at the time of current sink becomes maximum when the collector current I1 of the transistor 1202 is zero (I1 = 0), and the output current Iout at that time is the transistor 1
It becomes equal to the collector current of 205 (-A · Io). That is, the following equation is obtained. Iout = −A · Io

When the class AB amplifier forms a voltage follower with an input gain of 1, the relationship between the input voltage, the output voltage, and the through current (idling current) is the same as that in FIG.

According to the second embodiment, the sink current and the source current are the collector currents of NPN transistor 1205 for current sink and PNP transistor 1201 for current source, respectively, and the mirror transistor of transistor 1201 for current source. Since the current sink transistor 1205 is controlled by the transistor 1202, the output dynamic range of the class AB amplifier is equal to or higher than the Vsat of the transistor 1205 as in the conventional class A amplifier (see FIG. 9B). A voltage lower than Vcc by Vsat of the transistor 1201 (Vcc-Vsa
t) The range is as follows. For example, transistors 1201,
Assuming that Vsat of 1205 is 0.3 V and Vcc is 5 V, the output dynamic range of this class AB amplifier is 0.3 V to 4.7 V.

Further, according to the second embodiment, the idling current which affects the switching characteristics and the crossover distortion and the like at the time of current source and current sink is small, and is determined only by A, B and Io. Therefore, stabilization is easy.

Further, according to the second embodiment, since it can be used with a low power supply voltage and consumes low power,
It can be used as an analog amplifier in a ~ 5V power supply system, and is particularly suitable for a system such as a portable electronic device using a battery as a power supply.

Embodiment 3 FIG. 4 is a circuit diagram showing a configuration of the class AB amplifier according to the third embodiment of the present invention.
The third embodiment differs from the first embodiment in that a PNP transistor 301 and two NPN transistors 302 and 30 are used instead of the current amplification stage 208 in FIG.
3 (a portion surrounded by a broken line in FIG. 4) and a capacitor 304 is connected between the output terminal of the differential amplifier 206 and the output of the class AB amplifier. Other configurations are the same as those of the first embodiment shown in FIG. 1, and therefore, the same configurations are denoted by the same reference numerals and description thereof will be omitted.

The base terminal of the transistor 303 is short-circuited to its own collector terminal and is connected to the base terminal of the transistor 302. The emitter terminal of the transistor 303 is grounded, and the collector terminal thereof is connected to a constant current source 2 having one end connected to the power supply 209.
07 and to the collector terminal of the transistor 202. The transistor 303 forms a current mirror circuit together with the transistor 302.

The transistor 302 is different from the transistor 30
3 is a mirror transistor. The collector of the transistor 302 is connected to a short-circuit point between the collector and the base of the transistor 301. The emitter terminal of the transistor 302 is grounded.

The transistor 301 has an emitter terminal connected to the power supply 209, a base terminal short-circuited to its own collector terminal, and connected to the base terminal of the transistor 205.
05 together with a current mirror circuit.

The capacitor 304 is provided for phase compensation when the class AB amplifier operates.

Next, the operation of the third embodiment will be described. The operations of the differential amplifier 206 and the transistors 203, 202, 201, 205 at the time of current source and current sink are the same as those in the first embodiment, and the description will be omitted because they are duplicated. However, if the emitter area ratio between the transistor 205 and the transistor 301 is represented by n1, the current ratio determined by the area ratio between the transistor 201 and the transistor 202 and the resistance 204 is represented by n2, and the emitter area ratio between the transistor 302 and the transistor 303 is represented by n3, Is obtained by replacing A with the product of n1 and n3 (n1 · n3) and replacing B with n2 in the above equation (4), and is expressed by the following equation (7). Iout = n1.n3.Io- (n1.n3 + n2) .I1 where (0.ltoreq.I1.ltoreq. (N1.n3 / (n1.n3 + n2)). Io) (7)

The idling current (through current) Iid at the time of no load is obtained by setting Iout to zero (Iout =
0) and is expressed by the following equation (8).

On the other hand, the output current Iout at the time of current sink is
It is expressed by the following equation (9). Iout = n1 ・ n3 ・ Io- (n1 ・ n3 + n2) ・ I1 ((n1 ・ n3 / (n1ｎn3 + n2)) ・ Io ≦ I1 ≦ Io) (9)

The output current Iout at the time of current sink is represented by the following equation (10), where the beta amplification factors of the transistor 201 and the transistor 203 are BF3 and BF4, respectively. Iout = [output current of differential amplifier 206] .BF3.BF4 where (Iout <-n2.Io) (10)

FIG. 5 shows the relationship between the input voltage, the output voltage, and the through current (idling current) when the class AB amplifier forms a voltage follower with an input gain of 1.

According to the third embodiment, the first embodiment
The same effect can be obtained. That is, the output dynamic range of the class AB amplifier is the same as that of the conventional class A amplifier (FIG. 9).
As in the case of (b), the voltage is in the range of not less than Vsat of the transistor 201 and not more than Vcc-Vsat which is lower than Vcc by Vsat of the transistor 205 (FIG. 5).
(B)).

The reactive current at the time of current source and current sink is small, the value of the reactive current does not exceed the value determined by the above equation (8), and the idling current which affects the switching characteristics and crossover distortion is reduced. Since it is determined only by n1, n2, n3 and Io in equation (8), stabilization is easy. Therefore, according to the third embodiment, since it can be used at a low power supply voltage and consumes low power,
It can be used as an analog amplifier in a 2 to 5 V power supply system, and is particularly suitable for a system such as a portable electronic device using a battery as a power supply.

According to the third embodiment, if the emitter sizes of the transistors 301, 303, and 202 are minimized, the transistors 205, 302, and 201 and the resistor 204 are adjusted so that the source of the class AB amplifier is adjusted. Since the capability, sink capability, and idling current can be controlled, it is possible to set an idling current that is particularly stable with respect to temperature.

Further, according to the third embodiment, since the capacitor 304 is provided, an effect that the phase compensation effect is large can be obtained.

Embodiment 4 FIG. 6 is a circuit diagram showing a configuration of the class AB amplifier according to the fourth embodiment of the present invention.
The fourth embodiment differs from the second embodiment in that an NPN transistor 1301 and two PNP transistors 130 are used instead of the current amplification stage 1208 in FIG.
2, 1303, and a capacitor 1304 is connected between the output terminal of the differential amplifier 1206 and the output of the class AB amplifier. Other configurations are the same as those of the second embodiment shown in FIG. 3, and thus the same configurations are denoted by the same reference numerals and description thereof will be omitted.

The base terminal of the transistor 1303 is short-circuited to its own collector terminal and is connected to the base terminal of the transistor 1302. The emitter terminal of the transistor 1303 is connected to the power supply 1209, the collector terminal thereof is connected to the other end of the constant current source 1207 whose one end is grounded, and
202 is connected to the collector terminal. The transistor 1303 and the transistor 1302 form a current mirror circuit.

The transistor 1302 is a transistor 1
303 is a mirror transistor. Transistor 13
The collector of the transistor 02 is connected to the short-circuit point between the collector and the base of the transistor 1301. Transistor 1
The emitter terminal of 302 is connected to a power supply 1209.

Transistor 1301 has its emitter terminal grounded, its base terminal short-circuited to its own collector terminal, and is connected to the base terminal of transistor 1205, forming a current mirror circuit with transistor 1205. ing.

The capacitor 1304 is provided for phase compensation when the class AB amplifier operates.

Next, the operation of the fourth embodiment will be described. Differential amplifier 1206 and transistors 1203, 1202, 1201, 12 at the time of current source and current sink
The operation of 05 is the same as that of the second embodiment and will not be described because the description is redundant. Here, the emitter area ratio between the transistor 1205 and the transistor 1301 is n1, the current ratio determined by the area ratio between the transistor 1201 and the transistor 1202 and the resistance 1204 is n2, and the emitter area ratio between the transistor 1302 and the transistor 1303 is n.
When expressed as 3, the output current Iout at the time of the current source is obtained by replacing A with the product (n1 · n3) of n1 and n3 and replacing B with n2 in the above equation (6). ) Expression. Iout = (n1 · n3 + n2) · I1−n1 · n3 · Io ((n1 · n3 / (n1 · n3 + n2)) · Io ≦ I1 ≦ Io) (11)

The idling current (through current) Iid at the time of no load is obtained by setting Iout to zero (Iout
= 0) and is expressed by the following equation (12). Iid = (n1, n2, n3 / (n1, n3 + n2)). Io (12)

On the other hand, the output current Iout at the time of current sink is
It is expressed by the following equation (13). Iout = (n1 · n3 + n2) · I1−n1 · n3 · Io (0 ≦ I1 ≦ (n1 · n3 / (n1 · n3 + n2)) · Io) (13)

When the class AB amplifier forms a voltage follower having an input gain of 1, the relationship between the input voltage, the output voltage, and the through current (idling current) is the same as that shown in FIG.

According to the fourth embodiment, the second embodiment
The same effect can be obtained. That is, the output dynamic range of the class AB amplifier is the same as that of the conventional class A amplifier (FIG. 9).
As in (b), the Vsat of the transistor 1205 is
As described above, Vsat of the transistor 1201 is higher than Vcc.
Voltage (Vcc-Vsat) or lower.

The reactive current at the time of current source and current sink is small, the value of the reactive current does not exceed the value determined by the above equation (12), and the idling current which affects the switching characteristics and the crossover distortion is reduced. (12)
Since it is determined only by n1, n2, n3 and Io in the equation, stabilization is easy. Therefore, according to the fourth embodiment,
Since it can be used at a low power supply voltage and has low power consumption, it can be used as an analog amplifier in a system of a 2 to 5 V power supply system, and is particularly suitable for systems such as portable electronic devices using a battery as a power supply.

According to the fourth embodiment, if the emitter sizes of transistors 1301, 1303, and 1202 are minimized, transistors 1205, 1302, and
By adjusting the resistor 1201 and the resistor 1204, the source capability, sink capability and idling current of the class AB amplifier can be controlled, so that an idling current that is particularly stable with respect to temperature can be set.

Further, according to the fourth embodiment, since the capacitor 1304 is provided, an effect that the phase compensation effect is large can be obtained.

In the above, the present invention is not limited to the above embodiments, and it goes without saying that various designs can be changed, and MOS transistors may be used instead of bipolar transistors.

[0090]

As described above, according to the present invention, since the current source transistor is controlled by the mirror transistor with respect to the current sink transistor, the sink current and the source current are respectively equal to the current sink transistor. The current flows through the transistor and the current flowing through the current source transistor. Therefore this A
The output dynamic range of the class B amplifier is equal to or higher than the current sink transistor Vsat and lower than Vcc by the current source transistor Vsat (Vcc-V
sat) or less, and a class AB amplifier that can be used at a low voltage, for example, 2 V or less is obtained.

According to the present invention, since the current sink transistor is controlled by the mirror transistor for the current source transistor, the sink current and the source current are respectively the current flowing through the current sink transistor and the current source. Current flowing through the transistor. Therefore, the output dynamic range of the class AB amplifier is not less than Vsat of the transistor for current sink, and Vsa of the transistor for current source is higher than Vcc.
The range is lower than the voltage (Vcc-Vsat) lower by t, and a class AB amplifier which can be used at a lower voltage, for example, 2 V or lower can be obtained.

According to the present invention, the sink current and the source current are the collector current of the NPN bipolar transistor for current sink and the collector current of the PNP bipolar transistor for current source, respectively. The range is higher than Vsat of the transistor for current sink and lower than Vcc by Vsat of the transistor for current source (Vcc
−Vsat) or less, and a class AB amplifier that can be used at a low voltage, for example, 2 V or less is obtained.

According to the present invention, since the resistor for suppressing the saturation of the mirror transistor is provided,
Since the saturation of the mirror transistor is suppressed when it is necessary to allow the collector current of the mirror transistor to flow more, the output current of the class AB amplifier is a current corresponding to the current capability of the transistor mirrored by the mirror transistor. Is obtained.

According to the present invention, since the phase compensating capacitor is provided, the phase compensating effect when the class AB amplifier operates is large. A class amplifier is obtained.

According to the present invention, even when a MOS transistor is used, the sink current and the source current are the current flowing through the current sink transistor and the current flowing through the current source transistor, respectively. The dynamic range is a voltage (Vcc-Vsat) which is higher than Vsat of the transistor for current sink and lower than Vcc by Vsat of the transistor for current source.
A class AB amplifier which can be used at a low voltage, for example, 2 V or less is obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a class AB amplifier according to a first embodiment of the present invention;

FIG. 2 is a schematic diagram showing a relationship among an input voltage, an output voltage, and a through current for the class AB amplifier.

FIG. 3 is a circuit diagram illustrating a configuration of a class AB amplifier according to a second embodiment of the present invention;

FIG. 4 is a circuit diagram illustrating a configuration of a class AB amplifier according to a third embodiment of the present invention;

FIG. 5 is a schematic diagram showing a relationship between an input voltage, an output voltage, and a through current for the class AB amplifier.

FIG. 6 is a circuit diagram illustrating a configuration of a class AB amplifier according to a fourth embodiment of the present invention;

FIG. 7 is a circuit diagram showing a configuration of a conventional class A amplifier.

FIG. 8 is a circuit diagram showing a configuration of a conventional class AB amplifier.

FIG. 9 is a schematic diagram showing a relationship between an input voltage, an output voltage, and a through current for each of a conventional class A amplifier and a class AB amplifier.

[Explanation of symbols]

205, 1201 transistors for current source, 20
1,1205 transistors for current sink, 207,
1207 constant current source, 202, 1202 mirror transistor, 203, 1203 fourth transistor, 20
4,1204 Resistance for suppressing saturation, 304,1304 Capacitor for phase compensation.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J091 AA01 AA45 AA47 AA63 CA37 FA04 HA08 HA10 HA17 HA25 HA29 KA02 KA05 KA09 MA21 TA06

Claims (6)

[Claims] 1. A current source transistor for flowing a current toward an output side, a current sink transistor for extracting a current from an output side, and a current for driving the current source transistor A constant current source, of the currents passed by the constant current source, controlling the amount of current flowing to the current source transistor side to drive the current source transistor;
A mirror transistor through which a current corresponding to a current flowing through the current sink transistor flows; a fourth transistor controlling driving of the current sink transistor and driving of the mirror transistor in response to an external input; When the current flowing through the mirror transistor increases due to the fourth transistor, the current flowing through the current sinking transistor increases, and the driving current of the current source transistor decreases, thereby reducing the current source. When the current flowing through the mirror transistor decreases due to the fourth transistor, the current flowing through the current sink transistor decreases, and the current flowing through the current source transistor decreases. The drive current increases, and the current source A class AB amplifier characterized in that a current flowing through a star increases. 2. A current source transistor for flowing current toward the output side, a current sink transistor for extracting current from the output side, and a current capable of driving the current sink transistor. A constant current source, of the currents flown by the constant current source, controlling the amount of current flowing from the current sink transistor side to drive the current sink transistor, and the current source transistor A mirror transistor through which a current corresponding to the current flowing through the mirror transistor; and a fourth transistor that controls driving of the current source transistor and driving of the mirror transistor in response to an external input. 4 increases the current flowing through the mirror transistor, the current source The current flowing through the current sink transistor increases, and the drive current of the current sink transistor decreases to reduce the current flowing through the current sink transistor. On the other hand, the mirror transistor is controlled by the fourth transistor. An AB characterized in that when the flowing current decreases, the current flowing through the current source transistor decreases, and the driving current of the current sink transistor increases and the current flowing through the current sink transistor increases. Class amplifier. 3. The current source transistor comprises a PN transistor.
The AB according to claim 1 or 2, wherein the AB is a P-type bipolar transistor, and the transistor for current sink is an NPN-type bipolar transistor.
Class amplifier. 4. The mirror transistor according to claim 1, wherein a resistor for suppressing saturation of the mirror transistor is connected between a base terminal of the mirror transistor and an emitter terminal of the fourth transistor. 4. The class AB amplifier according to 2 or 3. 5. The input of said fourth transistor and said A
The class AB amplifier according to any one of claims 1 to 4, wherein a capacitor for phase compensation is connected between the output of the class B amplifier. 6. The transistor according to claim 1, wherein each of the transistors is a MOS transistor.
Class B amplifier.