JP2002009603A - Driver circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a driver circuit that can be operated by a required minimum current and easily applied to an integrated circuit with less effect of fluctuations in parameters of elements by supplying a base current to an output transistor(TR) in a required amount and at a required time. SOLUTION: The driver circuit is provided with a current source, consisting of TRs P2, P3 for supplying a collector correction to a pre-drive stage TR P1 and of a resistor R1, with a collector current detecting means consisting of a TR Q1 for detecting a collector current of the pre-drive stage TR, and with a current control means consisting of TRs Q2-Q4 for controlling the current source so as to keep the detected collector current to be a fixed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driver circuit, and more particularly to a driver circuit suitable for high integration in which a base current of an output transistor is compensated.

[0002]

2. Description of the Related Art In a conventional driver circuit, the base current of a transistor in an output stage through which a load current flows changes depending on hFE. Further, since the phase characteristics of the loop fluctuate depending on the load condition, the current of the pre-driver stage for driving the output stage must be set large. Preventing the hFE from decreasing in the output transistor increases the size of the output transistor, which directly affects the cost. Also, as the size increases, the parasitic capacitance increases,
Unless the current of the pre-drive stage is increased, the frequency characteristics deteriorate. When trying to improve the shortage of the driving capability, a vicious cycle of increasing the transistor size of the pre-drive stage, increasing the parasitic capacitance of the pre-drive stage, and deteriorating the frequency characteristics occurs. If the idling current of the output stage is not set large, the output distortion under a high load or at a high frequency is deteriorated. However, an idling current larger than a required current amount is necessary in consideration of variation. This also leads to an increase in transistor size, which contributes to a vicious cycle.

As described above, in the conventional bias circuit, the current of the pre-drive stage must be set in accordance with the maximum load current, and the bias current becomes large. In addition, a large bias current is required to compensate for the load drive ability in a state where the hFE is low, because the dependence on the variation of the element parameter (in particular, the hFE of the output stage transistor) is high. There is a circuit that improves this point and controls the current of the current source by detecting the amount of current to the load with a resistor.However, a low resistance is required to detect the load current, and it is difficult to apply it to an integrated circuit. there were. Furthermore, since the collector potential of the output stage transistor decreases due to the current detection resistor, there is a disadvantage that the characteristics are deteriorated when the power supply voltage is low.

[0004]

As described above, in the conventional driver circuit, since the current of the pre-drive stage is set in advance in accordance with the maximum load current and flows, a large bias current is required, and the circuit size is small. There was a problem of becoming larger. In order to avoid this, there is a method of detecting the load current and controlling the current of the pre-drive stage. However, the load current detection resistor needs to be low, and there are many problems in using it for an integrated circuit. There is also a problem that characteristics are deteriorated. The present invention solves this problem with a relatively simple configuration, supplies the required amount of base current to the output transistor when needed, minimizes the influence of variations in device parameters, and minimizes the required current. It is an object of the present invention to realize a driver circuit which can operate on an IC and can be easily applied to an integrated circuit.

[0005]

In order to achieve the above object, the present invention provides an emitter follower type output stage transistor for supplying a current to a load, and a pre-drive stage transistor for supplying a base current of the output stage transistor. In the driver circuit provided, a current source for supplying a collector (emitter) current to the predrive stage transistor, a collector current detection unit for detecting a collector current of the predrive stage transistor, and the collector current detection unit detect the current. Current control means for controlling the current source so as to maintain a collector current of the predrive stage transistor at a constant value.

Also, in a driver circuit including a collector output type output stage transistor for supplying a current to a load and a pre-drive stage for controlling a bias voltage of the output stage transistor and supplying a base current, Bias means for setting a bias voltage and supplying a base current; voltage comparing means for comparing an input voltage with a collector voltage of the output stage transistor; and a bias set by the bias means according to an output of the voltage comparing means. And a bias control means for controlling a voltage value and a base current value.

Furthermore, the emitter of an emitter follower type transistor whose collector is connected to a first power supply and the collector of a collector output type transistor whose emitter is connected to a second power supply are joined. A totem-pole output stage having a junction as an output terminal, a first pre-drive stage for supplying a base current to the emitter follower type transistor, and a base current by controlling a bias voltage of the collector output type transistor. In a totem-pole type driver circuit including a second pre-drive stage to be supplied, a collector current detection unit that detects a collector current of a transistor of the first pre-drive stage, and the collector current detection unit detects the collector current. First
Current control means for controlling the current source so as to maintain the collector current of the transistor of the predrive stage at a constant value; and a bias voltage of the collector output type output stage transistor provided in the second predrive stage. Biasing means for setting the voltage and supplying a base current; voltage comparing means for comparing an input voltage with the voltage at the junction; a bias voltage value and a base current set by the biasing means according to the output of the voltage comparing means Bias control means for controlling a value of the first pre-drive stage, wherein an output of the voltage comparison means is used as an input of a transistor of the first pre-drive stage.

Accordingly, it becomes possible to supply a required amount of a base current to be supplied to the output transistor when necessary, to reduce the influence of fluctuations in device parameters and to operate with a minimum necessary current. A driver circuit that can be easily applied to an integrated circuit is obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a driver circuit according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 shows an emitter-follower type load drive circuit conventionally used in general. According to this circuit configuration, when the load R1 becomes smaller, it is necessary to increase the current of the current source 12 and the base current of the NPN transistor Q1. In order to supply a necessary base current to the transistor Q1, it is necessary to increase the current of the current source I1. If the transistor P1 is changed to an NPN transistor, this problem is eliminated. However, since the amplitude of the output voltage is reduced, the PNP transistor must be used if the output voltage amplitude is to be increased as much as possible. In this case, the current I1 requires at least the maximum load current flowing through the resistor R1, the current I2, and the base current of the transistor Q1 determined by the hFE of the transistor Q1, and furthermore, the fluctuation of the hFE of the transistor Q1 and the transistor in the high current region. The current is determined including a margin in consideration of the decrease in hFE of Q1. If this circuit is part of a negative feedback amplifier circuit, more current is required to avoid signal phase rotation due to insufficient operating current of the transistor P1.

FIG. 3 shows a circuit in which this point is improved and the amount of current to the load is detected by the resistor R1 to control the current of the current source I1. According to this circuit, the current source I
Although it is possible to cope with a high load without setting an excessive current as 1, the voltage drop in the resistor R1 must be small enough not to affect the output voltage of the output stage.
A low resistance is required, which is inconvenient for IC.

FIG. 4 is a basic block diagram of the configuration of an emitter follower type driver circuit which does not use a low resistance, which is a drawback of the circuit of FIG. 3 of the present invention. The block configuration includes an output transistor Q1 and a transistor P1 for driving the output transistor Q1.
1. A voltage or current control current source I1 for determining the operating current of the transistor P1, a collector current detection circuit 11 for detecting a collector current of the transistor P1, a current source control circuit for detecting a deviation from a set value and controlling the current source 11 It consists of 12. This circuit indirectly detects whether the base current of the transistor Q1 is excessive or insufficient by detecting the collector current of the transistor P1. That is, the decrease / increase of the collector current of the transistor P1 is regarded as an excess or deficiency of the base current of the transistor Q1, and the current I1 is increased / decreased.
To compensate for the increase / decrease of the base current.

The operation of FIG. 4 will now be described.
Increases, the emitter potentials of the transistor P1 and the transistor Q1 increase. The emitter current of the transistor Q1 increases by an amount obtained by dividing the voltage increase by the load resistance R1. The base current of the transistor Q1 increases with an increase in the emitter current.
The part that becomes the emitter current is sucked. As a result, the collector current of the transistor P1 decreases, and the current detection circuit 1
At 1, a decrease is detected. With this signal as an input, the current source control circuit 12 generates a control signal so that the collector current of the transistor P1 returns to the set value, and the current source I1
As a result, the base current increase of the transistor Q1 is supplied, and the collector current of the transistor P1 returns to the set value. If the input voltage decreases, the opposite occurs, with the current I1 decreasing and absorbing the surplus current, but once the current I1 becomes zero, the transistor P1 thereafter absorbs the surplus current. According to this method, a relatively large resistance value can be used for the current detection circuit 11, so that it is more convenient to integrate the circuit than the circuit of FIG. 3, and the feature that the current consumption is small when there is no signal or the load is light remains. ing.

FIG. 1 shows an example of a specific configuration of the circuit shown in FIG. In this figure, transistor Q1 replaces current detection circuit 11 of FIG. 4 with transistors Q2, Q3 and Q4.
The current source control circuit 12 of FIG. 4 constitutes the current source I1 of FIG. 4 by the transistors P2 and P3 and the resistor R1. The operating current of the pre-driver stage is determined by the current multiplication factor of the current source I1 and the current mirror circuit of the transistors P2 and P3. The transistor P2 is (base current of the transistor Q5 in the output stage + emitter current of the transistor P1)
However, since the current detection circuit and the current source control circuit work to keep the collector current of the transistor P1 constant, the base current of the output stage transistor Q5 is compensated as a result.

Next, a collector output type circuit will be described. FIG. 5 shows a general collector output type circuit. The voltage control current source I1 converts an input signal into a current, and drives the output transistor Q2 via the driving transistor Q1. The voltage signal from the collector of the transistor Q2 is used as a feedback signal for making the output signal a voltage having a fixed ratio to the input signal. In this circuit configuration, like the emitter follower type, the transistor Q2
In consideration of the influence of the change in hFE and the change in the resistance R2, the voltage-current conversion gain of the voltage control current source I1 is increased to allow a large current to flow to cope with the fluctuation of the drive current. I have to put it. That is, in an actual circuit, the current is set so that an extra current can flow.

FIG. 6 is a block diagram showing a conventional circuit in which a signal from an output stage bias circuit 21 and a voltage control current source I1
And a bias control circuit 22 for controlling the output stage bias circuit 21 by using the signal from the input terminal as an input. The bias control circuit 22 controls the output stage bias circuit 21 so as to absorb fluctuations in hFE and resistance. As a result, the circuit current is optimized, the operation of each circuit section can be performed with the minimum necessary current, and the necessary current is supplied to the output stage when needed.

FIG. 7 shows this basic circuit. For simplicity, the circuit operation is treated as hFE = ∞. When the input voltage decreases, the collector current of the transistor P3 increases,
The base potential of transistor Q3 rises. Then, the transistor Q2 conducts, and the current to the transistor Q1 increases through the current mirror circuit including the transistor P1 and the transistor P2, and increases until the emitter potentials of the transistor Q1 and the transistor Q2 become substantially equal to the base potential of the transistor Q1. This allows
The base bias voltage of the output transistor Q4 increases,
Eventually, the collector current of transistor Q4 increases.
At this time, the current required for the P3 and P4 differential amplifiers is
If the current amplification factors of the P1 and P2 current mirror circuits are sufficiently high, it is possible to use only the minimum necessary current.

FIG. 8 shows a totem-pole push-pull output circuit in which the emitter follower type and the collector output type are combined. If this circuit combination,
The output current can be increased while the idling current is reduced, and the output voltage range can be increased. To maximize the output voltage range, both the PNP and the NPN transistor may be of a collector output type. However, in general, on a monolithic IC, the current capacity of the PNP transistor is low. Is advantageous.

In this circuit, a current source I1 and a resistor R
1, transistors P1 to P3, transistors Q1 to Q4
The output circuit of emitter-follower type composed of Q11 and Q11 has the same circuit configuration as that of FIG. 1, but the collector output type is such that the current source I1 in FIG. 7 is replaced by a current source I2, transistors Q5, Q8, Q9, Q10, It is replaced with a variable current source circuit using an NPN transistor composed of resistors R2 and R4. The addition of this circuit increases the operating current when the output circuit needs current,
It is possible to reduce the current when there is no signal, and to optimize it further than the basic circuit.

Since this circuit has two stable points, a transistor Q8 is added so as to operate reliably. Explaining mainly the circuit operation of this portion, when the power is turned on, the transistors Q8 and Q
Since no current is supplied from the transistor 9, the base bias voltage of the transistor Q12 is zero. When the current source I2 operates, the current from the I2 causes the transistor Q5
Generated at the base of the transistor Q8 and the resistor R
4 and is supplied to a differential amplifier composed of a transistor Q6 and a transistor Q7, a voltage is generated at the base of the transistor Q10,
Is biased, and a current flows through Q12.

When the input voltage decreases, the base voltage of the transistor Q7 increases, so that the collector current of the transistor Q7 increases, and the current is amplified by the current mirror circuit composed of the transistors P4 and P5 and the resistor R3.
The current to the bias circuit of the transistor Q10 and the resistor R4 increases, and the base voltage of the transistor Q12 increases. This increase in bias voltage causes the transistor Q1
2, the collector current of Q12 increases,
Lowers until equilibrium is reached. At this time, the transistor Q
Since the base voltage of the transistor 11 decreases and the emitter current decreases, no extra current flows into the transistor Q12.

When the input voltage increases, the base potential of the transistor Q11 rises and the base potential of the transistor Q7 drops, so that the current supplied to the transistor Q10 decreases and the collector current of the transistor Q12 decreases. No extra current is drawn from the transistor Q11.

As described above, since a required amount of base current is supplied, it is possible to drive a higher load with an output transistor size of the same area, and to improve the drive capability without increasing the chip area. be able to. Conversely, if the current driving capabilities are made equal, the area occupied by the output transistors can be reduced, so that the chip area can be reduced. Since the current flowing through the transistor of the pre-driver becomes constant, even when this output stage is included in the loop of the feedback amplifier, the amount of phase shift due to load fluctuation can be reduced and the capacitor for phase compensation can be reduced. is there.

[0024]

As described above, according to the first aspect of the present invention, an emitter-follower type output stage transistor for supplying a current to a load and a pre-drive stage transistor for supplying a base current of the output stage transistor are provided. In the driver circuit provided, a current source for supplying a collector (emitter) current to a pre-drive stage transistor, a collector current detection unit for detecting a collector current of the pre-drive stage transistor, and the pre-drive detected by the collector current detection unit Current control means for controlling the current source so as to maintain the collector current of the stage transistor at a constant value. By detecting the collector current of the pre-drive stage and controlling it to keep it constant, the base current to the output stage is increased or decreased according to the increase or decrease of the load current. Can be realized with a simple configuration. By detecting the current of the pre-driver stage, a low resistance conventionally required for detecting a load current is not required, which facilitates application to an integrated circuit, and furthermore, performance degradation hardly occurs even at a low power supply voltage.

According to a second aspect of the present invention, there is provided a driver having a collector output type output stage transistor for supplying a current to a load, and a predrive stage for controlling a bias voltage of the output stage transistor and supplying a base current. In a circuit, a bias means for setting a bias voltage of an output stage transistor and supplying a base current, a voltage comparison means for comparing an input voltage with a collector voltage of the output stage transistor, and a bias means according to an output of the voltage comparison means And a bias control means for controlling the set bias voltage value and base current value. Thus, by comparing the collector voltage of the output stage transistor with the input voltage, the base current to the output stage can be increased or decreased in accordance with the increase or decrease of the load current, and a low bias current and a high load drive capability can be realized. The driver circuit can be realized with a simple configuration. In addition,
The low resistance required for the detection of the load current is not required, which facilitates application to an integrated circuit, and furthermore, performance degradation hardly occurs even at a low power supply voltage.

According to a third aspect of the present invention, there is provided an emitter-follower-type transistor whose collector is connected to a first power supply and a collector-output-type transistor whose emitter is connected to a second power supply. A totem-pole type output stage in which a collector is connected to the collector, and the junction is used as an output terminal; a first pre-drive stage for supplying a base current to the emitter follower type transistor; and a bias voltage of the collector output type transistor Current detection means for detecting the collector current of the transistor of the first predrive stage in a totem-pole type driver circuit having a second predrive stage for controlling the power supply and supplying a base current; First detected by
Current control means for controlling the current source so as to maintain the collector current of the transistor in the pre-drive stage at a constant value, setting of the bias voltage of the collector output type output stage transistor provided in the second pre-drive stage, and Bias means for supplying a base current, voltage comparison means for comparing an input voltage with a voltage at a junction, and control of a bias voltage value and a base current value set by the bias means according to an output of the voltage comparison means. Bias control means, wherein the output of the voltage comparison means is used as the input of the transistor of the first pre-drive stage. Thereby, the base current to the output stage can be increased or decreased according to the increase or decrease of the load current, and the base current supplied to the output transistor is
Since it can supply only the required amount at the required time, the effect of parameter fluctuations of the elements that make up the circuit is reduced, and the driver circuit can operate with the minimum required current and achieve a large output voltage range. Can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an emitter-follower type driver circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional emitter follower type driver circuit.

FIG. 3 is a circuit diagram of a conventional emitter follower type driver circuit.

FIG. 4 is a circuit block diagram of an emitter follower type driver circuit of the present invention.

FIG. 5 is a circuit diagram of a conventional collector output type driver circuit.

FIG. 6 is a circuit block diagram of a collector output type driver circuit of the present invention.

FIG. 7 is a circuit diagram of a collector output type driver circuit according to another embodiment of the present invention.

FIG. 8 is a circuit diagram of a totem-pole type driver circuit according to still another embodiment of the present invention.

[Explanation of symbols]

11: collector current detection circuit, 12: current source control circuit,
21: output stage bias circuit, 22: bias control circuit,
C1 ... capacitors, I1, I2 ... current sources, P1 to P5 ...
PNP transistors, Q1 to Q12 ... NPN transistors, R1 to R5 ... resistors, VIN ... input signals.

Continued on the front page F-term (reference) 5H420 NA32 NA36 NB24 NB26 NC02 5J055 AX48 AX53 AX64 BX16 CX20 DX03 DX53 EX06 EX22 EY17 EZ03 EZ08 FX12 FX17 FX36 GX01 5J091 AA03 CA14 CA36 CA91 HA08 HA25 HA29 KA09 MA01 HA08 HA25 HA29 KA09 MA01 MA21 TA01

Claims (3)

[Claims] 1. A driver circuit comprising: an emitter follower type output stage transistor for supplying a current to a load; and a predrive stage transistor for supplying a base current of the output stage transistor. A) a current source for supplying a current; a collector current detecting means for detecting a collector current of the pre-drive stage transistor; and a collector current of the pre-drive stage transistor detected by the collector current detecting means being held at a constant value. And a current control means for controlling the current source. 2. A driver circuit comprising: a collector output type output stage transistor for supplying a current to a load; and a pre-drive stage for controlling a bias voltage of the output stage transistor and supplying a base current. Bias means for setting a bias voltage and supplying a base current; voltage comparing means for comparing an input voltage with a collector voltage of the output stage transistor; and a bias set by the bias means according to an output of the voltage comparing means. A driver circuit comprising: bias control means for controlling a voltage value and a base current value. 3. An emitter-follower-type transistor whose collector is connected to a first power supply and an emitter-collector-type transistor whose emitter is connected to a second power supply are connected to each other. A totem pole type output stage having a point as an output terminal, a first pre-drive stage for supplying a base current to the emitter follower type transistor, and a base current supplied by controlling a bias voltage of the collector output type transistor A totem-pole type driver circuit including a second pre-drive stage, wherein: a collector current detection unit for detecting a collector current of the transistor of the first pre-drive stage; 1 so that the collector current of the transistor in the pre-drive stage is maintained at a constant value. Current control means for controlling a source; bias means for setting a bias voltage of the collector output type output stage transistor provided in the second pre-drive stage and supplying a base current; Voltage comparison means for comparing voltages; and bias control means for controlling a bias voltage value set by the bias means and a base current value in accordance with an output of the voltage comparison means, wherein an output of the voltage comparison means is provided. Is an input of the transistor of the first pre-drive stage.