JP5414382B2 - Output circuit - Google Patents

Description

  The present invention relates to an output circuit, and more particularly, to an improvement in driving capability, improvement in frequency characteristics, and the like.

Conventionally, as this type of circuit, for example, a grounded emitter class AB output circuit (rail-to-rail output circuit) constructed by connecting the collectors of an NPN transistor and a PNP transistor to each other is good. It is known (see, for example, Non-Patent Document 1).
FIG. 3 shows a configuration example of such a conventional grounded emitter class AB output circuit. The conventional circuit will be described below with reference to FIG.
An amplifier 101A is provided in the previous stage of this grounded emitter class AB output circuit, and the output stage of the amplifier 101A is connected to the base of the PNP output transistor Q1A.

The collectors of the PNP output transistor Q1A and the NPN output transistor Q2A are connected to each other, and a load resistor R4 is connected between the connection point and the ground so that an output signal can be output. Yes.
The base potential of the PNP output transistor Q1A is biased by a circuit composed of a PNP third transistor Q3A, diodes D1A and D2A, and a current source I1, while the PNP output transistor Q2A Is biased by a circuit comprising an NPN-type fourth transistor Q4A, diodes D3A and D4A, and a current source I4.

  In such an output circuit, when the output potential is lower than the ground (GND), the output transistor Q2A sinks the current from the load resistor R4, and the base current Ib2 of the output transistor Q2A that increases when the current is sucked is 3 is supplied from the amplifier 101A through the third transistor Q3A.

  On the other hand, when the output potential is higher than the ground, the output transistor Q1A discharges the current to the load resistor R4, and the base current Ib1 of the output transistor Q1A, which increases when the current is discharged, passes through the third transistor Q3A. Supplied from the amplifier 101A.

WCM RENIRIE, KJ DELANGEN, AND JH HUIJSING, Parallel Feedforward Class-AB Control Circuits for Low-Voltage Bipolar Rail-to-Rail Output Stages of Operational Amplifiers, Analog Integrated Circuits and Signal Processing, USA, Kluwer Academic Publishers, 1995, No. No. 8, p. 37-48

By the way, in such a conventional circuit, the upper limit value of the current discharge / sink in the output stage is determined by the driving capability of the amplifier 101A in the previous stage that supplies the base currents Ib1, Ib2 of the output transistors Q1A, Q2A generated during the current discharge / sink. Therefore, the value of the load resistor R4 depends on the driving capability of the amplifier 101A.
On the other hand, since the driving capability of the amplifier 101A is in a trade-off relationship with the consumption current, when the consumption current is limited, the driving capability of the amplifier 101A cannot be easily improved. Therefore, the load resistor R4 There was a problem that the resistance value of this could not be reduced easily.

  Further, when the output voltage fluctuates to the power supply voltage VCC and the ground voltage VEE, the output multi-transistors Q1A and Q2A are saturated, the DC current amplification factor HFE is reduced, and the base currents Ib1 and Ib2 of the output transistors Q1A and Q2A are reduced. However, when the drive capability of the amplifier 101A cannot be sufficiently ensured as described above, there is a problem that the output voltage cannot sufficiently swing between the power supply voltage VCC and the ground voltage VEE.

  For example, as a countermeasure when the driving capability of the amplifier 101A cannot be sufficiently secured, there is a method of increasing the emitter areas of the output transistors Q1A and Q2A in order to prevent the base currents Ib1 and Ib2 from increasing. There is a disadvantage that the parasitic capacitance between the base and collector of the transistors Q1A and Q2A is increased, thereby causing a new problem of deterioration of frequency characteristics.

The present invention has been made in view of the above circumstances, and provides an output circuit capable of improving drive capability and frequency characteristics without being affected by the drive capability of an amplifier provided at the first stage of the output circuit. It is.
Another object of the present invention is to provide an output circuit having good frequency characteristics while reducing the driving capability of an amplifier provided in the previous stage as compared with the conventional one.

In order to achieve the above object of the present invention, an output circuit according to the present invention includes:
A transconductance amplifier to which an input signal is input, a collector grounded class AB output circuit to which the output signal of the amplifier is input, and a level shift circuit for converting the signal level of the output signal of the collector grounded class AB output circuit; A grounded emitter class AB output circuit to which the output signal of the level shift circuit is input ,
Those formed by the can suppress the output saturation of the common-emitter class AB output circuit by the current amplification of the signal at each of said level shift circuit and the collector grounded type AB class output circuit.

  According to the present invention, a grounded collector class AB output circuit and a level shift circuit are provided between the amplifier provided in the previous stage of the grounded emitter type class AB output circuit and the input stage of the grounded emitter type class AB output circuit. Therefore, it is possible to substantially increase the driving capability of the amplifier with respect to the grounded emitter class AB output circuit without increasing the driving capability of the amplifier itself, and the emitter area of the output transistor of the grounded emitter type AB output circuit. This eliminates the need for adopting a conventional method for ensuring the driving capability of the amplifier by increasing the frequency, and thus has an effect that the frequency characteristics can be improved as compared with the conventional method.

It is a block diagram which shows the basic structural example of the output circuit in embodiment of this invention. It is a circuit diagram which shows the example of a specific circuit structure of the output circuit in embodiment of this invention. It is a circuit diagram which shows the circuit structural example of a conventional circuit.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2.
The members and arrangements described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.
First, a basic configuration example of the output circuit in the embodiment of the present invention will be described with reference to FIG.
The output circuit in the embodiment of the present invention includes an amplifier 101 to which an input signal is input, a collector grounded class AB output circuit 102 to which the output of the amplifier 101 is input, and an output of the collector grounded class AB output circuit 102. A level shift circuit 103 for level-shifting the signal and a grounded emitter class AB output circuit 104 for inputting the output of the level shift circuit 103 are provided.

FIG. 2 shows a specific circuit configuration example, which will be described below with reference to FIG.
First, the amplifier 101 to which the input signal to the output circuit in the embodiment of the present invention is input is basically the same as that provided in the previous stage of the conventional output circuit, and a so-called transconductance amplifier is provided. It has been used.
The grounded collector class AB output circuit 102 has basically the same configuration as a well-known configuration.
That is, the collector-grounded class AB output circuit 102 includes NPN-type ninth and twelfth transistors (indicated as “Q9” and “Q12” in FIG. 2) 9 and 12, respectively, and a PNP-type tenth output circuit 102. And eleventh transistors (represented as “Q10” and “Q11” in FIG. 2, respectively) 10, 11 and eighth and ninth constant current sources (in FIG. 2, “I8”, “I9”, respectively). ”And 28, 29.

The ninth and tenth transistors 9 and 10 are connected to the input stage of the next level shift circuit 103 with their emitters connected to each other, while the collector of the ninth transistor 9 is applied with the power supply voltage VCC. The ground potential VEE is applied to the collector of the tenth transistor 10.
The base of the ninth transistor 9 is connected to the emitter of the eleventh transistor 11, and an eighth constant current source 28 is connected between the emitter of the eleventh transistor 11 and the power supply voltage VCC. Is provided. The ground potential VEE is applied to the collector of the eleventh transistor 11.

Further, the base of the eleventh transistor 11 is connected to the output stage of the amplifier 101 together with the base of the twelfth transistor 12.
The emitter of the twelfth transistor 12 is connected to the base of the tenth transistor 10, and a ninth constant current source 29 is provided between the emitter and the ground potential VEE.

  Next, the level shift circuit 103 includes NPN-type fifth and sixth transistors (indicated as “Q5” and “Q6” in FIG. 2) 5 and 6, respectively, and PNP-type seventh and eighth transistors. Transistors (referred to as “Q7” and “Q8” in FIG. 2, respectively) 7 and 8 and fifth to seventh constant current sources (“I5”, “I6”, and “I7” in FIG. 2 respectively) And 25), 26, 27, and a constant voltage source 31.

The fifth and sixth transistors 5 and 6 are provided to form a current mirror.
That is, the bases of the fifth and sixth transistors 5 and 6 are connected to each other and to the collector of the fifth transistor 5, while the collector of the fifth transistor 5 and the power supply voltage VCC A fifth constant current source 25 is provided in between, and a sixth constant current source 26 is provided between the collector of the sixth transistor 6 and the power supply voltage VCC. The connection point between the sixth transistor and the sixth constant current source 26 is connected to a grounded emitter class AB output circuit 104 described later.

  The emitter of the fifth transistor 5 is connected to the emitter of the seventh transistor 7 described below, and the emitter of the sixth transistor 6 is connected to the emitter of the eighth transistor 8 described below. The emitters of the sixth and eighth transistors 6 and 8 are connected to the emitters of the ninth and tenth transistors 9 and 10 of the grounded collector class AB output circuit 102 described above.

On the other hand, the seventh and eighth transistors 7 and 8 are also provided to form a current mirror.
That is, the bases of the seventh and eighth transistors 7 and 8 are connected to each other and to the collector of the seventh transistor 7, while the collector of the seventh transistor 7 and the ground potential VEE are A constant voltage source 31 is provided in between, and a seventh constant current source 27 is provided between the collector of the eighth transistor 8 and the ground potential VEE.
A connection point between the collector of the eighth transistor 8 and the seventh constant current source 27 is connected to a grounded emitter class AB output circuit 104 described below.

  Next, the grounded-emitter class AB output circuit 104 includes PNP-type first and third transistors (indicated as “Q1” and “Q3” in FIG. 2) 1 and 3, respectively, and an NPN-type second transistor. And the fourth transistors (indicated in FIG. 2 as “Q2” and “Q4”, respectively) 2 and 4, and the first to fourth diodes (in FIG. 2, “D1”, “D2”, “ D3 ”and“ D4 ”) 15 to 18 and first to fourth constant current sources (represented as“ I1 ”,“ I2 ”,“ I3 ”, and“ I4 ”in FIG. 2, respectively) 21 to 24.

The PNP type first transistor 1 and the NPN type second transistor 2 constituting the output stage have their collectors connected to each other, and a resistor (in FIG. 1) is connected between this connection point and the ground. Is expressed as “R1”) 32 is connected to obtain an output signal.
The power supply voltage VCC is applied to the emitter of the first transistor 1, while the ground potential VEE is applied to the emitter of the second transistor 2.

The collector of the sixth transistor 6 of the previous level shift circuit 103 is connected to the base of the first transistor 1, while the base of the second transistor 2 is connected to the second transistor of the level shift circuit 103. The collectors of the eight transistors 8 are connected.
On the other hand, the first and second diodes 15 and 16 are connected in order from the power supply voltage VCC to the first diode 15 and the second diode 16 so that the anode is on the power supply voltage VCC side. A first constant current source 21 is provided between the second cathode and the ground potential VEE.

A connection point between the cathode of the second diode 16 and the first constant current source 21 is connected to the base of the third transistor 3.
The collector of the third transistor 3 is connected to the base of the second transistor 2, and a second constant current source 22 is provided between this connection point and the ground potential VEE.
On the other hand, the emitter of the third transistor 3 is connected to the base of the first transistor 1, and a third constant current source 23 is provided between this connection point and the power supply voltage VCC.

In addition, a fourth constant current source 24 and third and fourth diodes 17 and 18 are sequentially connected in series from the power supply voltage VCC side between the power supply voltage VCC and the ground potential VEE. The third diode 17 has an anode connected to the fourth constant current source 24 and a cathode connected to the anode of the fourth diode 18. The ground potential VEE is applied to the cathode of the fourth diode 18. It has become so.
The connection point between the fourth constant current source 24 and the third diode 17 is connected to the base of the fourth transistor 4, and the collector of the fourth transistor 4 is connected to the first transistor 1. While connected to the base, the emitter of the fourth transistor 4 is connected to the base of the second transistor 2.

Next, the operation in this configuration will be described.
First, when the output potential obtained at the connection point between the collectors of the first and second transistors 1 and 2 is higher than the ground, the current to the resistor 32 is discharged by the first transistor 1. The base current Ib 1 that increases at this time flows into the tenth transistor 10 of the collector-grounded class AB output circuit 102 via the sixth transistor 6 in the level shift circuit 103.

The current discharge capability of the output circuit, that is, the capability of allowing the base current Ib1 of the first transistor 1 to flow into the collector-grounded class AB output circuit via the level shift circuit 103 which is the preceding stage is, in other words, The maximum value Ib1max is determined and can be obtained as Ib1max = I9 × HFE (Q10). Here, I9 is assumed to be the emitter current of the ninth transistor 9 for convenience. HFE (Q10) is the DC current gain of the tenth transistor 10.
The current discharge capability of the amplifier 101 is I9 / HFE (Q12) = Ib1max / (HFE (Q10) × HFE (Q12)).

On the other hand, when the output potential obtained at the connection point between the collectors of the first and second transistors 1 and 2 is lower than the ground, current flows from the resistor 32 to the second transistor 2, The current is drawn. The base current Ib2 that increases when the current is sucked by the second transistor 2 is supplied from the ninth transistor 9 of the collector-grounded class AB output circuit 102 via the eighth transistor 8 in the level shift circuit 103. The Rukoto.

In such a case, the maximum value Ib2max of the base current that can flow into the base of the second transistor 2 is determined as Ib2max = I8 × HFE (Q9).
Here, I8 is assumed to be the collector current of the eighth transistor 8 for convenience. HFE (Q9) is the direct current amplification factor of the ninth transistor 9.
In this case, the current sink capability of the amplifier 101 is I8 / HFE (Q11) = Ib1max / {HFE (Q11) × HFE (Q9)}.
Here, HFE (Q11) is the direct current amplification factor of the eleventh transistor 11.

Thus, for example, in the conventional circuit as shown in FIG. 3, the driving capability required for the amplifier 101A is Ib1max and Ib2max, but in the output circuit in the embodiment of the present invention, As described above, the magnitude of 1 / (HFE (Q11) × HFE) is sufficient with respect to the conventional current.
In addition, when the output voltage fluctuates to the power supply voltage VCC and the ground voltage VEE, the first and second transistors 1 and 2 are saturated, and even if the DC current amplification factor HFE is significantly reduced, the amplifier 101 has a driving capability of 1 / (HFE × HFE) of the base current Ib1 of the first transistor 1 and the base current Ib2 of the second transistor 2, and the eighth and ninth constant current sources of the shift level circuit 103 are provided. By supplying currents I9 = Ib1max / HFE (Q10) and I8 = Ib2max / HFE (Q9) to 28 and 29, respectively, it becomes possible to swing to VCC and VEE.

  Further, as described above, the amplifier 101 has a drive capability of 1 / (HFE × HFE) of the base currents Ib1 and Ib2, and the eighth and ninth constant current sources 28 and 29 have I9 = Ib1max / HFE, respectively. (Q10), the current of I8 = Ib2max / HFE (Q9) is made to flow, and unlike the conventional case, the drive area of the amplifier 101 is compensated by increasing the emitter areas of the first and second transistors 1 and 2. Therefore, the parasitic capacitance between the base and collector of the first and second transistors 1 and 2 can be reduced, so that the frequency characteristics are improved as compared with the conventional method. Become.

DESCRIPTION OF SYMBOLS 101 ... Amplifier 102 ... Collector ground type AB class output circuit 103 ... Level shift circuit 104 ... Grounded emitter class AB output circuit

Claims (1)

A transconductance amplifier to which an input signal is input, a collector grounded class AB output circuit to which the output signal of the amplifier is input, and a level shift circuit for converting the signal level of the output signal of the collector grounded class AB output circuit; A grounded emitter class AB output circuit to which the output signal of the level shift circuit is input ,
Output circuit characterized by comprising as a can suppress the output saturation of the common-emitter class AB output circuit by the current amplification of the signal at each of said level shift circuit and the collector grounded type AB class output circuit.

Images