JPH11112246A - Output circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an output circuit for class AB amplification capable of reducing chip area and improving characteristics at a high frequency area. SOLUTION: This circuit is constituted of an output NPN transistor(TR) Q14 that is driven by a positive polarity signal of an input signal Vin and provides an output of an output signal Vout from an output terminal Tout, an output NPN TR Q15 whose polarity is the same as that of the output NPN TR Q14 and that is driven by a negative polarity signal of the signal Vout and provides an output of the output signal Vout from the output terminal Tout, and a control circuit section 110 that drives the output NPN TR Q14 when the input signal Vin is positive to supply an idling current to the output NPN Tr Q15 and produces a control signal to drive the output NPN TR Q15 in response to the input signal Vin when the input signal Vin is negative.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output circuit, and more particularly, to an output circuit for performing a class AB amplification operation.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing an example of a conventional output circuit. A conventional output circuit 1 for performing class AB operation includes a shift circuit 2 for shifting an input signal, a first output circuit unit 3 driven on the plus side of the input signal, and a second output circuit unit 3 driven on the minus side of the input signal. It comprises an output circuit section 4.

The shift circuit 2 is connected to the input terminal Tin and shifts up the center level of the input signal supplied to the input terminal Tin to a level at which the first output circuit section 3 operates. The shift circuit 2 includes a PNP transistor Q1, an NPN
Transistor Q2, PNP transistor Q3, resistor R1
Consists of The transistors Q1 and Q2 have their collector and base short-circuited and function as diodes.

A base and a collector of the transistor Q1 function as a cathode of the diode and are connected to an input terminal Tin to which an input signal is supplied, and an emitter functions as an anode of the diode and is connected to an emitter of the transistor Q2. Note that the emitter of the transistor Q2 functions as the cathode of the diode. The base and collector of transistor Q2 act as an anode and are connected to the collector of transistor Q3.

[0005] The transistor Q3 forms a constant current source together with the resistor R1. In the transistor Q3, the power supply voltage Vcc is applied to the emitter via the resistor R1, the bias voltage VBB is applied to the base, a constant current is output from the collector, and the constant current is supplied to the base and the collector of the transistor Q2. A constant current flows through the transistors Q1 and Q2, a forward current flows through the transistors Q1 and Q2,
A constant voltage is generated between the base and the collector of the transistor Q1 and the base and the collector of the transistor Q2.

[0006] The first output circuit section 3 comprises an NPN transistor Q5 and a resistor R2. Transistor Q5
The power supply voltage Vcc is applied to the collector, the emitter is connected to the output terminal Tout via the resistor R2, and the base is connected to the connection point between the transistors Q2 and Q3 of the shift circuit 2. The base potential of the transistor Q5 is shifted by the shift circuit 2, and supplies an idling current to the output terminal Tout when the input signal is at the reference level.

[0007]

However, in the conventional output circuit, a PNP transistor is used as an output circuit for controlling the negative side of the input signal.
When the transistor is made into an IC, the drive capability is low,
In order to balance with the NPN transistor, it is necessary to enlarge the pattern. For this reason, the chip area increases, the parasitic capacitance and the frequency characteristics deteriorate,
There are problems such as deterioration of characteristics in a high frequency region.

FIG. 5 shows a frequency characteristic diagram of an example of a conventional output circuit. As shown in FIG. 5, when trying to extend the frequency characteristics, a phenomenon occurs in which the gain temporarily increases near the cutoff frequency f0 due to the large parasitic capacitance parasitic on the PNP transistor. The present invention has been made in view of the above points, and has as its object to provide an output circuit that can reduce a chip area and improve characteristics in a high-frequency region.

[0009]

According to a first aspect of the present invention, there is provided a driving circuit which is driven when an input signal has one polarity, and outputs an output signal corresponding to one polarity of the input signal from an output terminal. One output transistor, a second output transistor having the same polarity as the first output transistor and outputting an output signal from the output terminal in accordance with the other polarity of the input signal, and one of the polarity of the input signal. Control means for turning off the second output transistor when the polarity is negative, and generating a control signal for driving the second output transistor in accordance with the input signal when the polarity of the input signal is the other polarity And characterized in that:

According to the first aspect, when the polarity of the input signal is one polarity by the first output transistor, an output signal corresponding to the input signal is output from the output terminal, and the polarity of the input signal is controlled by the control means. When one polarity, the second output transistor having the same polarity as the first output transistor is turned off, and when the polarity of the input signal is the other polarity, the second output transistor is driven according to the input signal. By doing
The first and second output transistors can be composed of, for example, NPN transistors having excellent high-frequency characteristics.

Preferably, the control means includes a third transistor having a base connected to a base of the first output transistor, and an emitter connected to an emitter of the first output transistor; A first voltage source that holds a collector of the transistor at a first potential, a fourth transistor having an emitter connected to a connection point between the third transistor and the constant voltage source, and a fourth transistor. A second voltage source that holds the base of the second transistor at a second potential, and a control circuit that controls the base potential of the second output transistor in accordance with the collector current of the fourth transistor. .

According to the second aspect, the control means includes a third transistor having a base connected to the base of the first output transistor, and an emitter connected to the emitter of the first output transistor; A first voltage source that holds a collector of the transistor at a first potential, a fourth transistor having an emitter connected to a connection point between the third transistor and the constant voltage source, and a fourth transistor. And a control circuit that controls the base potential of the second output transistor in accordance with the collector current of the fourth transistor, thereby providing an input. Third depending on the signal
And the collector potential of the third transistor controls the emitter potential of the fourth transistor, while the base potential of the fourth transistor is controlled by the second voltage source. Therefore, the base-emitter voltage of the fourth transistor is controlled by the input signal, the collector current of the fourth transistor is controlled by the input signal, and the collector current of the fourth transistor is supplied to the control circuit. Controlling the base potential of the second output transistor according to the collector current of the fourth transistor, and controlling the second output transistor according to the input signal when the polarity of the input signal is the other polarity. Can be.

Preferably, the first and second output transistors and the control means are formed on an NP formed on a semiconductor substrate.
It is characterized by being composed of N transistors. According to the third aspect, the first and second output transistors and the control means are formed on a semiconductor substrate, and the first and second output transistors are formed of NPN transistors. Is generally P
Since the size is smaller than the NP transistor and the high-frequency characteristics are good, the size of the semiconductor substrate can be reduced, the high-frequency characteristics of the circuit can be improved, and high-frequency signals can be handled.

[0014]

FIG. 1 is a circuit diagram of an embodiment of the present invention. The output circuit 100 of the present embodiment includes an NPN transistor Q14 corresponding to a first output transistor in the claims, an NPN transistor Q15 corresponding to a second output transistor in the claims, And a control circuit unit 110 corresponding to the control means. In the output circuit 100 of the present embodiment, the input signal Vin is supplied to the input terminal Tin. The input signal Vin supplied to the input terminal Tin is supplied to the base of the NPN transistor Q14 and the control circuit unit 110.

The power supply voltage Vcc is applied to the collector of the transistor Q14, and the emitter is connected to the output terminal Tout. The transistor Q14 is turned on when the input signal Vin has a positive polarity, and supplies an emitter current corresponding to the input signal Vin to the output terminal Tout. The control circuit unit 110 includes an NPN transistor Q13 corresponding to a third transistor in the claims, an NPN transistor Q9 corresponding to a fourth transistor in the claims, and a first constant transistor in the claims. An NPN transistor Q12 corresponding to a voltage source, an NPN transistor Q6, PNP transistors Q7, Q8, and a resistor R constituting a second constant voltage source in the claims.
4. It comprises NPN transistors Q10 and Q11 and resistors R5 and R6 corresponding to the control circuit in the claims.

In the control circuit section 110, the input terminal Tin is
Connected to the base of transistor Q13. The transistor Q13 has an emitter connected to the output terminal Tout and a collector connected to the emitter of the transistor Q12. Transistor Q12
The power supply voltage Vcc is applied to the collector and the base, and the collector of the transistor Q13 is kept at a constant potential with respect to the power supply voltage Vcc.

The connection point between the emitter of the transistor Q12 and the collector of the transistor Q13 is connected to the emitter of the transistor Q9. The emitter potential of the transistor Q9 is controlled according to the potential at the connection point between the emitter of the transistor Q12 and the collector of the transistor Q13, that is, the input signal Vin. The base of the transistor Q9 is connected to the base and the collector of the transistor Q7. The transistor Q7 has a base and a collector connected to the collector of the transistor Q6, and an emitter connected to the emitter of the transistor Q8. Transistor Q6
Has a predetermined bias voltage VBB applied to its base, and the emitter is grounded via a resistor R4. Therefore, the transistor Q6 draws the constant current I1 from the collector.

The transistor Q8 has a collector and a base connected to each other, and functions as a diode. The power supply voltage V is applied to the collector and base of the transistor Q8.
cc is applied. For this reason, a current flows forward in the PN junction between the base and the emitter of the transistor Q8 by the power supply voltage Vcc, and a forward voltage is generated in the PN junction between the base and the emitter. The emitter potential of transistor Q7 is held at a predetermined potential by transistor Q8.

A constant current I1 flows between the base and the emitter of the transistor Q7 by the transistor Q6, and a constant voltage VA is generated at the collector and the base. The constant voltage VA generated at the collector and the base of the transistor Q7 is applied to the base of the transistor Q9. Transistor Q
A collector current 9 flows when the emitter potential VB becomes larger than the base potential VA due to the input voltage Vin, and turns off when the emitter potential VB becomes smaller than the base potential VA due to the input voltage Vin, and the collector current is stopped. The collector of transistor Q9 is connected to the collector of transistor Q10 and the base of transistor Q11.

The transistor Q10 has an emitter connected to a resistor R5.
, And the base is connected to the base of transistor Q15. In the transistor Q11, the power supply voltage Vcc is applied to the collector, the base is connected to the collector of the transistor Q10, and the emitter is connected to the connection point between the base of the transistor Q10 and the base of the transistor Q15. Further, a connection point between the base of the transistor Q10 and the base of the transistor Q15 is grounded via a resistor R6.

Transistors Q10 and Q11, resistors R5 and R6
Constitutes a current mirror together with the transistor Q15, amplifies the current of the collector of the transistor Q9, and draws it from the output terminal Tout. Next, the output circuit 100
Will be described with reference to the drawings. FIG. 2 shows an operation waveform diagram of one embodiment of the present invention. 2A shows the input signal Vin, FIG. 2B shows the emitter current of the transistor Q14, and FIG.
(C) is the collector current of transistor Q13, FIG.
2E is an emitter potential VB of the transistor Q9, FIG. 2E is a collector current of the transistor Q9, FIG. 2F is a base potential of the transistor Q15, and FIG.
FIG. 2H shows the waveform of the output signal Vout.

At time T1, when the input voltage Vin changes with a positive polarity, as shown in FIG.
14 is driven to supply a current corresponding to the input voltage Vin to the output terminal Tout. At this time, the transistor Q13 saturates,
The emitter current of the transistor Q12 is used as the collector current of the transistor Q13 as shown in FIG.
supplied to out. Therefore, the emitter potential VB of the transistor Q9 is set to the low level as shown in FIG. 2D, and is lower than the base potential VA of the transistor Q9.

When the emitter potential VB of the transistor Q9 becomes low level and is lower than the base potential VA of the transistor Q9, the transistor Q9 is turned off. As shown in FIG. 2E, the collector of the transistor Q9 is idling. A current flows according to the current. When the collector of the transistor Q9 decreases, the transistor Q11
2 is turned off, the base potential of the transistor Q15 becomes low level as shown in FIG. 2 (F), the transistor Q15 is turned off, and the collector current of the transistor Q15 is changed to the level shown in FIG.
As shown in (G), only the idling current flows.

Therefore, from the output terminal Tout, FIG.
(H), the emitter current of the transistor Q14,
That is, an output signal Vout corresponding to the input signal Vin is output. When the input voltage Vin changes with a negative polarity at the time T2, the transistor Q14 is turned off as shown in FIG. At this time, when the input voltage Vin becomes negative, the transistor Q12 enters the operation region, and a current according to the input signal Vin flows through the collector of the transistor Q13 as shown in FIG. For this reason, the emitter potential VB of the transistor Q9 fluctuates according to the input voltage Vin as shown in FIG.

When the emitter potential VB of the transistor Q9 increases, the collector current of the transistor Q9 increases as shown in FIG.
As shown in (E), a current flows according to the emitter potential VB. The collector current of the transistor Q9 is supplied to the bases of the transistors Q10 and Q15 via the transistor Q11, and changes the base potentials of the transistors Q10 and Q15 according to the input signal Vin as shown in FIG.

For this reason, the collector current of the transistor Q15 is changed according to the signal shown in FIG.
The current is varied as shown in (G), and a current is drawn from the output terminal Tout. Therefore, from the output terminal Tout, FIG.
An output signal Vout as shown in (H) is output. At this time, the idling current is determined as follows.

First, the base potential VA of the transistor Q9 is determined by the bias current I1. On the other hand, the ratio of the emitter area between the transistor Q13 and the transistor Q14 is
Since 1: n is set, (1 / n) current of the output transistor Q14 is drawn from the collector of the transistor Q13, and the emitter potential VB of the transistor Q9 is determined.

The potential difference (V.sub.V) between the base potential VA and the emitter potential VB is applied between the base and the emitter of the transistor Q9.
B-VA) is applied. The collector current of the transistor Q9 is a current corresponding to the potential difference (VB-VA) between the base potential VA and the emitter potential VB. Further, a current mirror circuit including the transistors Q10, Q11, Q15 and the resistors R5, R6 amplifies the collector current of the transistor Q9. Therefore, the idle current is equal to the base potential VA.
The difference is determined by the potential difference (VB-VA) between the current and the emitter potential VB, and the current amplification factor of the current mirror circuit including the transistors Q10, Q11 and Q15, and the resistors R5 and R6.

Therefore, the idle current can be set, for example, by the ratio of the emitter area of the transistor Q10 to the emitter area of the transistor Q15, m: n, and the resistance R5. In this embodiment, the output dynamic range is Vcc-2Vces-Vbe, where Vcc is the power supply voltage, Vces is the collector-emitter voltage when the transistors Q14 and Q15 are saturated, and Vbe is the base-emitter voltage of the transistor. Is determined.

Therefore, the output dynamic range can be increased as compared with the related art. According to the present embodiment,
The part where the driving capability is required, that is, the transistor Q
14, Q15 can be constituted by an NPN transistor. Therefore, when an IC is formed, it can be configured with a parasitic capacitance smaller than that of the PNP transistor. For this reason, high frequency characteristics can be improved.

FIG. 3 shows a frequency characteristic diagram of one embodiment of the present invention. According to the present embodiment, the parasitic capacitance can be reduced as compared with the case where the output transistor is constituted by the PNP transistor. Therefore, as shown by the solid line in FIG. Can be prevented, and the high-frequency characteristics can be improved.

As an application example of this embodiment, for example, a feedback amplifier can be configured in combination with a differential amplifier.

[0033]

As described above, according to the first aspect of the present invention, when the polarity of the input signal is one polarity by the first output transistor, an output signal corresponding to the input signal is output from the output terminal. When the polarity of the input signal is one polarity by the control means,
Is turned off, and when the polarity of the input signal is the other polarity, the second output transistor is driven according to the input signal, so that the first and second output transistors have, for example, high frequency characteristics. It has such features that it can be composed of excellent NPN transistors.

According to the second aspect, the control means includes a third transistor having a base connected to a base of the first output transistor, and an emitter connected to an emitter of the first output transistor; A first voltage source that holds a collector of the transistor at a first potential, a fourth transistor having an emitter connected to a connection point between the third transistor and the constant voltage source, and a fourth transistor. And a control circuit that controls the base potential of the second output transistor in accordance with the collector current of the fourth transistor, thereby providing an input. The second according to the signal
And the collector potential of the second transistor controls the emitter potential of the third transistor, while the base potential of the third transistor is controlled by the second voltage source. Therefore, the base-emitter voltage of the third transistor is controlled by the input signal, the collector current of the third transistor is controlled by the input signal, and the collector current of the third transistor is supplied to the control circuit. Controlling the base potential of the second output transistor according to the collector current of the third transistor, and controlling the second output transistor according to the input signal when the polarity of the input signal is the other polarity. Features such as the ability to

According to the third aspect, the first and second output transistors and the control means are formed on a semiconductor substrate, and the first and second output transistors are formed of NPN transistors. In general, NPN transistors are smaller in size than PNP transistors and have good high-frequency characteristics, so that the size of the semiconductor substrate can be reduced, the high-frequency characteristics of the circuit can be improved, and high-frequency signals can be handled.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is an operation waveform diagram of one embodiment of the present invention.

FIG. 3 is a frequency characteristic diagram of one embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional example.

FIG. 5 is a frequency characteristic diagram of an example of the related art.

[Explanation of symbols]

 Reference Signs List 100 output circuit 110 control circuit section Q6, Q8, Q10 to Q15 NPN transistor Q7, Q9 PNP transistor R4 to R6 Resistance

Claims (3)

[Claims] A first output transistor that is driven when the polarity of the input signal is one polarity and outputs an output signal from an output terminal according to one polarity of the input signal; and the first output transistor. A second output transistor that outputs an output signal corresponding to the other polarity of the input signal from the output terminal, the second output transistor having the same polarity as the second output transistor when the input signal has one polarity. And an output circuit for generating a control signal for driving the second output transistor in accordance with the input signal when the input signal is off and the polarity of the input signal is the other polarity. 2. The control means includes: a third transistor having a base connected to a base of the first output transistor, and an emitter connected to an emitter of the first output transistor; A first voltage source for holding a collector at a first potential, a fourth transistor having an emitter connected to a connection point between the third transistor and the constant voltage source, and a base of the fourth transistor. 2. A control circuit, comprising: a second voltage source that holds a second potential; and a control circuit that controls a base potential of the second output transistor in accordance with a collector current of the fourth transistor. Output circuit as described. 3. The first and second output transistors,
The control means is formed on a semiconductor substrate, and includes the first
3. The output circuit according to claim 1, wherein the second output transistor comprises an NPN transistor.