JPH1032437A - Power amplifier - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To achieve both high output and high stability even under a low power supply voltage, and to enable a significant reduction in external components. [Structure] A push-pull output circuit is formed by a bipolar transistor forming an inverted Darlington connection circuit, and a feedback capacitor forming a local negative feedback circuit by the inverted Darlington connection circuit and a phase around the entire amplifier. A phase-advancing capacitor for suppressing oscillation is formed integrally on the semiconductor substrate, and the feedback capacitor is formed with a capacitance including a dielectric film having a higher dielectric constant than silicon dioxide, and the phase-advancing capacitor is formed in the semiconductor substrate. It is formed with a PN junction capacitance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology effective when applied to a power amplifier, and further to a BTL audio power amplifier IC (semiconductor integrated circuit device). It relates to technology that is effective for car audio.

[0002]

2. Description of the Related Art For example, a power amplifier for car audio is required to be able to stably drive a speaker whose impedance state fluctuates rapidly with a relatively low power supply voltage supplied from a vehicle-mounted battery.
Further, in the case of the IC, it is required to reduce the number of external components as much as possible in order to reduce the size of the device or the system and to reduce the cost.

A conventional power amplifier obtains a high output by an output stage formed by a push-pull connection of a pair of power bipolar transistors each connected in a Darlington connection in the forward direction, and has a large capacitance element and a low resistance value. By connecting a snubber circuit in which the resistance elements are connected in series to the output terminal in parallel, the operation is stabilized.

[0004] This type of power amplifier is disclosed, for example, in "Basic Transistor Amplifier Design Method" 2
It is described on pages 4 to 255 (AB class audio power amplifier).

[0005]

However, it has been clarified by the present inventors that the above-described technology has the following problems.

That is, in the conventional power amplifier, the bipolar transistors forming the push-pull output circuit at the output stage are Darlington connected in the forward direction.
The base of each transistor that makes the Darlington connection
The emitter-to-emitter voltage is added, which increases the apparent saturation voltage of the output transistor interposed in series between the power supply potential and the output terminal or between the output terminal and the reference potential,
The output voltage amplitude with respect to the power supply voltage becomes small.
As a result, there is a problem that a high output cannot be obtained under a low power supply voltage.

In order to stably drive a load such as a loudspeaker having a large impedance variation without inducing oscillation, it is effective to connect a snubber circuit to the output terminal as described above. Since the snubber circuit requires a very large-capacitance element and a low-resistance resistor,
It is difficult to convert to C, and therefore, it has to be provided externally. This has been a major impediment to miniaturization and cost reduction of the device or system due to the reduction in external components.

Here, with respect to increasing the output under a low power supply voltage, the present inventors set the output stage transistors to PNP and N
We considered a Darlington connection, which is a so-called inverted Darlington connection combining PN bipolar transistors. In this inverted Darlington, it is possible to avoid an increase in the saturation voltage due to the addition of the base-emitter voltages of the transistors connected in Darlington. As a result, the output voltage amplitude can be increased to near the power supply voltage, and high output can be achieved even under a low power supply voltage.

However, the operation of the inverted Darlington connection circuit is unstable, unlike the aforementioned forward Darlington connection circuit, that is, the normal Darlington connection circuit. For this reason, there is a contradictory problem that the operation becomes unstable, such as oscillation, while the output is increased due to the increase in the output voltage amplitude.

An object of the present invention is to provide a technique capable of achieving both high output and high stability even under a low power supply voltage and greatly reducing external parts. It is in.

The above and other objects and features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0012]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, in a power amplifier in which a push-pull output circuit and its driving circuit are integrated on a single silicon semiconductor substrate, the push-pull output circuit is formed by bipolar transistors forming an inverted Darlington connection circuit. Together with the above inverted
A feedback capacitor forming a local negative feedback circuit in the Darlington connection circuit, and a phase advance capacitor for suppressing oscillation around the entire phase of the amplifier are formed on the semiconductor substrate, and the feedback capacitor is higher than silicon dioxide. The capacitor is formed by a capacitance including a dielectric film having a dielectric constant, and the phase advance capacitor is formed by a PN junction capacitance in the semiconductor substrate.

According to the above-described means, the operation of the inverted Darlington connection circuit and the whole amplifier can be stabilized even when no stabilizing component such as a snubber circuit is externally connected to the output terminal.

As a result, the object of achieving both high output and high stability even at a low power supply voltage and achieving a significant reduction in external components can be achieved.

A typical embodiment of the present invention is an NPN-type first transistor (Q1) having a collector-emitter path connected between a first operating potential point (P3) and an output terminal (P4). An NPN-type second transistor (Q2) having a collector-emitter path connected between the output terminal (P4) and a second operating potential point (P5); and a base of the first transistor (Q1). A third PNP transistor (Q3) having a collector connected to the PNP transistor; a fourth PNP transistor (Q4) having a collector connected to the base of the second transistor (Q2); An NPN-type fifth transistor (Q5) having an emitter connected to the emitter of the transistor (Q4);
Of the transistor (Q5) and the output terminal (P
4) and a bias diode (Q6
A) and a first bias circuit (BC1) including the first transistor (Q1) are formed on one semiconductor substrate forming a semiconductor integrated circuit, and the base of the first transistor (Q1) is the same as that of the third transistor (Q3). The second transistor (Q2) is driven by a collector signal, and the base of the second transistor (Q2) is driven by a collector signal of the fourth transistor (Q4), so that the first transistor (Q1) and the second transistor ( Q2) is a power amplifier performing a push-pull operation, wherein a first capacitor (C1) is connected between the base and collector of the third transistor (Q3), and the base of the second transistor (Q2) is connected. A second capacitor (C2) is connected between the collectors, and the bias diode (Q) of the first bias circuit (BC1) is connected
A third capacitor (C3) is connected between both ends of 6A), and the first capacitor (C1) and the second capacitor (C2) are formed by a capacitor including a dielectric film having a higher dielectric constant than silicon dioxide. The third capacitor (C3) is formed on each of the semiconductor substrates, and the third capacitor (C3) is formed by a PN junction capacitor in the semiconductor substrate (see FIG. 1).

A more specific embodiment of the present invention further has the following features.

The bias diode (Q6A) of the first bias circuit (BC1) is an NPN-type sixth transistor (6) of the first bias circuit (BC1).
B) is connected between the base and collector of the sixth transistor (Q6B), and the collector-emitter path of the sixth transistor (Q6B) is connected to the fifth transistor (Q6B).
Of the transistor (Q5) and the output terminal (P
4).

The base of the third transistor (Q3) and the base of the fourth transistor (Q4) are driven by output signals of a drive stage amplifier (DRA) formed on the semiconductor substrate, respectively, and (DR
A) is an NPN-type seventh transistor (Q7), an emitter-grounded NPN-type eighth transistor (Q8) whose base is Darlington-connected to the emitter of the seventh transistor (Q7), 7 transistors (Q
7) a fourth capacitor (C4) connected between the base of the eighth transistor (Q8) and the collector of the eighth transistor (Q8).

The semiconductor substrate is provided with a differentially connected NP
N-type ninth and tenth transistors (Q9, Q10)
And a voltage follower circuit (VFC) including a collector of the ninth transistor (Q9) and a load resistor (R7) connected between the first operating potential point and the driving circuit. The output signal of the stage amplifier (DRA) is transmitted to the base of the ninth transistor (Q9) of the voltage follower circuit (VFC),
The third transistor (Q3) operates as a collector load of the transistor (Q10), and the collector and base of the tenth transistor (Q10) are short-circuited, so that the ninth and tenth transistors (Q9) , Q
10) is characterized by operating as a voltage follower.

The drive stage amplifier (DRA) further includes a second bias circuit (BC2) connected to the collector of the eighth transistor (Q8) and load means (CS2). The output signal of the drive stage amplifier (DRA) appearing at the collector of the transistor (Q8) is:
The voltage is transmitted to the base of the ninth transistor (Q9) of the voltage follower circuit (VFC) via the second bias circuit (BC2).

The second bias circuit (BC2) has an emitter connected to the collector of the eighth transistor (Q8) and a collector connected to the voltage follower circuit (V2).
FC) and an NPN-type eleventh transistor (Q11) connected to the base of the ninth transistor (Q9).
And a first resistor (R) connected between the base of the eleventh transistor (Q11) and the load means (CS2).
1) a second resistor (R2) connected between the base and the emitter of the eleventh transistor (Q11);
A third resistor (R) connected between the collector of the eleventh transistor (Q11) and the load means (CS2).
3).

The output signal of the drive stage amplifier (DRA) appearing at the collector of the eighth transistor (Q8) is:
Through the resistor (Rb4), the fourth transistor (Q
It is characterized by being transmitted to the base of 4).

The high dielectric constant dielectric films of the first capacitor (C1) and the second capacitor (C2) are made of silicon nitride.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 1 shows an embodiment of a power amplifier to which the technique of the present invention is applied.

The power amplifier shown in FIG. 1 forms an audio power amplifier having a speaker as a load, and is provided in a semiconductor integrated circuit device IC using a silicon semiconductor substrate.

In FIG. 1, P1 and P2 are signal input terminals, P3 is a supply terminal for a power supply voltage Vcc, P4 is a signal output terminal, and P5 is a ground terminal connected to a ground potential serving as a reference potential. In this case, the power supply potential Vcc forms a first operating potential point, and the ground potential forms a second operating potential point.

In the IC, a differential amplifier DFA, NPN-type bipolar transistors Q1, Q2, Q5, Q6B,
Q7 to Q11, PNP type bipolar transistor Q3
Q4, Q6C, resistors R1 to R4, Rb4, R6A, Re
9, Re10, Rf1, Rf2, constant current circuits CS1 to CS3 forming load means, a diode Q6A, capacitors C1 to C4, and the like.

NPN transistors Q1 and Q2 form the final stage of a class B push-pull output circuit. One NP
The N-type transistor Q1 has its collector-emitter path connected between the power supply terminal P3 and the output terminal P4. The other NPN transistor Q2 has its collector-emitter path connected between the output terminal P4 and a ground terminal P5 forming a second operating potential point.

At the same time, the base of one NPN transistor Q1 is driven by the collector signal of PNP transistor Q3. Similarly, the base of the other NPN transistor Q2 is driven by the collector signal of the PNP transistor Q4.

That is, one NPN transistor Q1
Has a base connected to the collector of the PNP transistor Q3 to form an inverted Darlington connection circuit. Similarly, the collector of the PNP transistor Q4 is connected to the base of the other NPN transistor Q2 to form an inverted Darlington connection circuit. The two inverted Darlington connection circuits form a push-pull output circuit of the power amplifier. In this case, Q1 and Q3 form a push circuit (PUSH CKT), and Q2 and Q4 form a pull circuit (PULLKT), respectively.

On the pull circuit side, a PNP transistor Q4, which is a preceding stage of the Darlington connection circuit, has an emitter connected to the emitter of an NPN transistor Q5.
The NPN transistor Q5 has a collector connected to the power supply terminal P3 and a base connected to the constant current circuit CS1 and the first bias circuit BC1.

The constant current circuit CS1 is a load means and supplies a constant current from the power supply terminal P3. This constant current is shunted to the base of the transistor Q5 and the first bias circuit BC1.

The first bias circuit BC1 comprises a bias diode Q6A connected in the forward direction from the first operating potential point to the second operating potential point, and a resistor R6A inserted in series on the cathode side of the diode Q6A. , This resistor R6
An NPN transistor Q6B, to which a base current is supplied through A, and a P connected in series between the base and collector and connected in series to the NPN transistor Q6B.
It is formed by an NP transistor Q6C or the like.
It is connected between the base of the PN transistor Q5 and the output terminal P4.

The capacitors C1 and C2 are made of silicon nitride (Si
3N4) is formed by a capacitor using a dielectric film. This silicon nitride has a higher dielectric constant than silicon dioxide. By including this dielectric film, a non-polar capacitor having a large capacitance of, for example, 100 pF and having no polarity dependence can be obtained. The silicon nitride film can be formed on the above semiconductor substrate. The capacitor C3 is formed by the PN junction capacitance in the semiconductor substrate. These capacitors C1 to C3 are connected as follows.

That is, the first capacitor C1 is connected to the PN which is the former stage of the Darlington connection circuit on the push circuit side.
It is connected between the base and the collector of the P-type transistor Q3. The second capacitor C2 is connected to an NPN transistor Q which is a subsequent stage of the Darlington connection circuit on the pull circuit side.
It is connected between two base collectors. The third capacitor C3 is connected between both ends of the bias diode Q6A and the resistor R6A of the first bias circuit BC1.

The bases of the transistors Q3 and Q4, which are the preceding stages of the Darlington connection circuit, are respectively driven by the output signals of the driving stage amplifier DRA formed on the semiconductor substrate.

The driving stage amplifier DRA is constituted by NPN transistors Q7 and Q8 forming a Darlington connection circuit. Q7 has a collector connected to a power supply terminal P3 via a resistor R4, and an emitter connected to Q8.
It is connected to the base of Turlington. The collector of Q8 is connected to a power supply terminal P3 via a second bias circuit BC2 and a constant current circuit CS2 as load means, respectively.
It is connected to the. At the same time, a fourth capacitor C4 is connected between the collector of Q8 and the base of Q7. The fourth capacitor C4 is formed by a capacitance using silicon nitride (Si3 N4) as a dielectric film.

The second bias circuit BC2 forms a kind of a level dividing circuit, and includes a driving stage amplifier DR2.
The output signal of A is divided into two signals that are level-shifted from each other and output. The signal shifted to the high level is input to the voltage follower circuit VFC, and the signal shifted to the low level is input to the base of the transistor Q4 of the pull circuit via the resistor Rb4.

The second bias circuit BC2 has an NPN
It comprises a transistor Q11 and resistors R1 to R3. The emitter of Q11 is connected to the collector of the transistor Q8 of the driving stage amplifier DRA, and is connected to the base of the transistor Q4 of the pull circuit via the resistor Rb4. The collector is connected to the base of the transistor Q9 of the voltage follower circuit VFC. The resistor R1 is connected between the base of Q11 and a constant current circuit CS2 serving as a load. Resistance R2
Is connected between the base and emitter of Q11, and the resistor R3 is connected between the collector of Q11 and the constant current circuit CS2.

The voltage follower circuit VFC is connected to the second
The output signal voltage of the drive stage amplifier DRA shifted to the high level side by the bias circuit BC2, that is, the signal voltage appearing at the collector of Q11 is transmitted to the base of the transistor Q3 of the push circuit.

This voltage follower circuit VFC
It is composed of NPN transistors Q9, Q10 and the like. The emitters of Q9 and Q10 are commonly connected via emitter resistors Re9 and Re10, respectively, and this common connection point is connected to a ground potential (second operating potential point) via a constant current circuit CS3 which is a load means. . This gives Q
9 and Q10 form a differential circuit coupled between the emitters. The base of one transistor Q9 of this differential circuit is connected to the collector of transistor Q11 of the second bias circuit BC2, and the collector and base of the other transistor Q10 are short-circuited (commonly connected). A voltage negative feedback circuit having a voltage gain of 1 is formed, and a voltage follower operation of outputting a voltage input to the base of Q9 from the collector of Q10 is performed.

At this time, the PNP transistor Q3, which is a preceding stage of the push-side inverted Darlington connection circuit, operates as a collector load of the transistor Q10 of the voltage follower circuit VFC.

Next, the operation will be described.

In FIG. 1, input signals supplied from input terminals P1 and P2 are amplified by a differential amplifier DFA. The output signal of the differential amplifier DFA is class-A amplified by the Darlington connection transistors Q7 and Q8 of the driving stage amplifier DFA. This class A amplified output signal is Q3
Q1 push circuit (PUSH CKT) and Q4, Q2
Class B power is amplified by a Class B push-pull output circuit comprising a pull circuit (PULL CKT). This amplified output signal is output from the output terminal P4 as a final amplified output signal.

At this time, the push circuit (PUSH CK)
T) is a set of a PNP transistor Q3 and an NPN transistor Q1, as described above, so that the maximum value of the final amplified output signal from the output terminal P4 can swing to a level very close to the power supply voltage Vcc. It is composed of an inverted Darlington connection circuit by combination. This inverted Darlington connection circuit can make the apparent saturation voltage extremely lower than that of a normal Darlington connection circuit composed of NPN transistors or PNP transistors.

As for the pull circuit (PULL CKT), in order to make the final output signal at the output terminal P4 swing to a level very close to the ground potential, similarly to the push circuit side, a PNP transistor Q4 and an NPN transistor It is configured using an inverted Darlington connection circuit based on a combination of Q2.

As a result, the output voltage amplitude width can be expanded to the very end of the power supply voltage range, and as a result, the power supply voltage utilization efficiency can be increased and the output can be increased.

In this case, in order to make the final output signal at the output terminal P4 swing to a level very close to the power supply voltage Vcc on the push circuit side, the final-stage transistor Q1
Needs to be as close as possible to the power supply voltage Vcc.
Although the Darlington connection circuit is effective, in order to bring the base supply voltage of the final transistor Q1 closer to the power supply voltage Vcc, the circuit shown in FIG. 1 is used as a collector load means of the NPN transistor Q9 of the voltage follower circuit VFC. , And a resistor R7. as a result,
The PNP transistor Q3, which is a stage preceding the push-side inverted Darlington connection circuit, is driven to near the saturation region. As a result, the base supply voltage of Q1 can be further shifted to the vicinity of power supply voltage Vcc.

In a class B push-pull power amplifier, so-called crossover distortion occurs near the intersection of the polarities of the output voltages. In order to reduce this crossover distortion, a minute DC current, that is, an idling current, is caused to flow through the collector-emitter paths of the final-stage transistors Q1 and Q2 in a no-signal state. This DC idling current is set by the two bias circuits BC1 and BC2 described above.

The second bias circuit BC2 is connected to the base-emitter voltage (Vbe) of the NPN transistor Q11.
Is increased by the ratio of the resistors R1 and R2, and the bias voltage is reduced by the resistor R3 to generate a bias voltage. This bias voltage is supplied to the base of the transistor Q1 at the subsequent stage of the push-side inverted Darlington connection circuit via the Holtage follower circuit VFC. At this time, the resistor R3
Acts to reduce the change in the bias voltage with respect to the change in the power supply voltage Vcc.

The first bias circuit BC1 has a bias diode Q6A, transistors Q6B and Q6C, and is connected between the output terminal P4 and the base of the transistor Q5. In the second bias circuit BC2, a change in the voltage between the base and the emitter is offset between Q5 and Q6B, between Q4A and Q6A, and between Q4 and Q6C. .

The voltage gain of the entire power amplifier is determined by the feedback resistance R
It is set by the values of f1 and Rf2.

In the power amplifier described above, local feedback is performed by the capacitors C1 and C2 in the inverted Darlington connection circuits on the push side and the pull side, respectively, and the phase advance capacitor C3 is connected to the bias circuit BC1.
, It is possible to prevent local oscillation in the inverted Darlington connection circuit and to prevent oscillation due to phase rotation in the entire class B push-pull amplifier. Each of the three capacitors C1, C2, and C3 has a considerably large internal capacitance of about 100 pF.

One end of the capacitor C1 used in the push-side inverted Darlington connection circuit is connected to the collector of the transistor Q9 of the voltage follower circuit VFC, and the collector voltage of the Q9 is connected to the power supply voltage Vcc. It varies greatly from a very close value to a much lower value. Therefore, a polarity-dependent PN junction capacitance cannot be used for the capacitor C1. However, with a silicon dioxide dielectric film obtained by oxidizing a silicon semiconductor, 100 pF
Forming a large-capacity capacitor requires a considerably large electrode area. Therefore, by using silicon nitride (Si3 N4) having a higher dielectric constant than silicon dioxide for the dielectric film, a large-capacity capacitor that can cope with a wide voltage change and has no polarity is formed. The silicon nitride dielectric film can be formed by nitriding silicon (Si) in an IC manufacturing process. Thus, 10
Even a non-polar capacitor of 0 pF can be formed with a relatively small area in an IC. One end of the capacitor C2 used in the pull-side inverted Darlington connection circuit is connected to the output terminal P4. The voltage of the output terminal P4 changes substantially from the power supply voltage Vcc to the ground voltage. For this reason, the PN junction capacitance cannot be used for the pull-side capacitor C2, and a capacitance formed using silicon nitride (Si3 N4) as a dielectric film is used as in the case of the push-side capacitor.

Regarding the phase advance capacitor C3 used in the first bias circuit BC1, since the resistor R6A connected to the bias diode Q6A is a relatively small resistor of 1 kΩ, the voltage across the capacitor C3 is It can be considered that the forward voltage of Q6A is clamped to 0.7V. Therefore, the phase-advancing capacitor C3 has a large capacitance P even with a small area.
An N-junction capacitor is used. This PN junction capacitor can be formed using the junction capacitance between the P-type base diffusion layer and the N-type emitter diffusion layer of the NPN bipolar transistor.

In the driving stage amplifier DRA, a phase compensation capacitor C4 is connected between the collector of Q8 and the base of Q7. This capacitor C4 includes capacitors C1 and C2.
Similarly, a capacitor using silicon nitride (Si3 N4) of about 13 pF as a dielectric film is used.

Next, the operation of the local feedback capacitors C1 and C2 and the phase advance capacitor C3 will be described.

In the push-side inverted Darlington connection circuit, when a snubber circuit is not connected to the output terminal P4, a relatively large output is generated by connecting a speaker cable or the like in parallel with an inductive load such as a speaker at the output terminal P4. When a capacitive load such as a stray capacitance is connected, oscillation tends to occur in the push-side final-stage transistor Q1 that operates as an emitter follower. At this time, the capacitor C1 is connected to Q
When the local negative feedback of the push-side inverted Darlington connection circuit is performed by connecting between the base and the collector of Q3, the output impedance of Q3 changes from inductive to capacitive, and the high-frequency gain of Q3 decreases. Oscillation is prevented.

In the pull-side inverted Darlington connection circuit, the capacitor C2 connected between the collector and the base of the pull-side last-stage transistor Q2 absorbs a high-frequency signal from the output terminal P4, thereby driving the capacitive load. The swell of the frequency characteristic from the push-side final transistor Q1 at the time is suppressed. At this time, the capacitance of the capacitor C2 viewed from the output terminal P4 is expanded according to the amplification of the transistor Q2. Further, even if power noise is injected into the base of the pull-side final transistor Q2, the capacitor C2 bypasses the output terminal P4 so that the power noise is not amplified by Q2.

The base of the PNP bipolar transistor Q4 of the pull-side inverted Darlington connection circuit is connected in series with an oscillation prevention resistor Rb4 of about 1 kΩ to reduce the roll-off frequency of the Q4. , A kind of phase compensation is formed. This gives Q
No connection is required for the phase compensation capacitance between the base and the collector of No. 4.

The phase advance capacitor C3 of the first bias circuit BC1 suppresses the phase rotation of the entire B push-pull amplifier to prevent oscillation.

As described above, in a power amplifier in which a push-pull output circuit and its driving circuit are integrated on the same silicon semiconductor substrate, the push-pull output circuit is a bipolar transistor forming an inverted Darlington connection circuit. And a feedback capacitor forming a local negative feedback circuit in the inverted Darlington connection circuit, and a phase advance capacitor for suppressing oscillation around the entire phase of the amplifier are integrally formed on the semiconductor substrate. The feedback capacitor is formed with a capacitance including a dielectric film having a higher dielectric constant than silicon dioxide, and the phase-advancing capacitor is formed with a PN junction capacitance in the semiconductor substrate to stabilize a snubber circuit or the like at an output terminal. Even if you do not attach any external components, the inverted Darlington connection circuit and The operation of the entire fine amplifier can be stabilized. As a result, even under a low power supply voltage, high output and high stability can be achieved at the same time, and the number of external components can be significantly reduced.

FIG. 2 shows an application example of the power amplifier shown in FIG. 1 to an audio system. In the figure, 10
0 is a semiconductor integrated circuit device (IC) using a single silicon semiconductor substrate, 1 is the power amplifier shown in FIG.
Reference numeral 11 denotes a phase division circuit, and SP denotes a speaker as a load. Eight power amplifiers 1 are integrally formed in one semiconductor integrated circuit device 100. 8 power amplifiers 1,
1, 1,..., 1 are divided into four sets of two, and each set forms a BTL audio power amplifier.

The audio power amplifier of the BTL system converts an input signal Vin into two signals of a normal phase and a negative phase + Vi
n, -Vin, and the two phase-divided signals are respectively power-amplified by the power amplifiers 1 and 1. The output Vout of one power amplifier 1 is connected to one pole of a speaker, and the other power amplifier is connected to the other power amplifier. One output Vout is formed by connecting the output Vout to the other pole of the speaker, so that one speaker can be power-driven in both forward and reverse directions.

In the example shown in FIG. 2, eight power amplifiers 1, 1, 1,... 1 and four phase division circuits 11,.
, 11, B for 4 channels (CH1 to CH4)
A TL audio / power amplifier circuit is integrally formed.

Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and can be variously modified without departing from the gist thereof. Needless to say.

In the above description, the case where the invention made by the inventor is applied to an audio power amplifier, which is the application field as the background, has been mainly described. However, the present invention is not limited to this. It can be applied to other power drive circuits.

[0071]

The following is a brief description of an outline of typical inventions among the inventions disclosed in the present application.

That is, even under a low power supply voltage, high output and high stability can be achieved at the same time.
The effect is obtained that the number of external components can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a power amplifier to which the technology of the present invention is applied.

FIG. 2 is a circuit diagram showing an application example of the power amplifier of the present invention.

[Explanation of symbols]

 IC semiconductor integrated circuit device P1, P2 signal input terminal P3 supply voltage Vcc supply terminal (first operating potential point) P4 signal output terminal P5 ground terminal (second operating potential point) Q1 NPN bipolar transistor Q2 NPN bipolar transistor Q5 NPN-type bipolar transistor Q6B NPN-type bipolar transistor Q7 to Q11 NPN-type bipolar transistor Q3 PNP-type bipolar transistor Q4 PNP-type bipolar transistor Q6C PNP-type bipolar transistor R1-R4 Resistance Rb4 Resistance R6A Resistance Re9, Re10 Resistance Rf1, CS2 Constant current circuit forming load means Q6A Diode C1, C2, C3 Capacitor (silicon nitride dielectric film) C3 Capacitor (PN junction capacitance) PUSH CK Push circuit PULL CKT-pull circuit BC1 first bias circuit BC2 second bias circuit DFA differential amplifier DRA driver stage amplifier VFC voltage follower circuit

Continued on the front page (72) Inventor Ritsuji Takeshita Semiconductor Company, Hitachi Ltd. 5-2-1, Kamizuhoncho, Kodaira City, Tokyo (72) Inventor Shoichi Hosoda 15 Asahidai, Muroyamacho, Iruma-gun, Saitama Address Sun Inside Eastern Eastern Semiconductor Co., Ltd.

Claims (8)

[Claims] An NPN-type first transistor having a collector-emitter path connected between a first operating potential point and an output terminal; and a collector-emitter connected between the output terminal and a second operating potential point. An NPN-type second transistor having a path connected thereto, a PNP-type third transistor having a collector connected to the base of the first transistor, and a PNP having a collector connected to the base of the second transistor A fourth transistor of the NPN type; a fifth transistor of the NPN type having an emitter connected to the emitter of the fourth transistor; and a bias transistor connected between the base of the fifth transistor and the output terminal. A first bias circuit including a diode is formed on one semiconductor substrate forming a semiconductor integrated circuit; and a base of the first transistor is provided. Is driven by the collector signal of the third transistor, and the base of the second transistor is driven by the collector signal of the fourth transistor, so that the first transistor and the second transistor are pushed. A power amplifier that performs a pull operation, wherein a first transistor is provided between a base and a collector of the third transistor.
Is connected between the base and the collector of the second transistor.
A third capacitor is connected between both ends of the bias diode of the first bias circuit. The first capacitor and the second capacitor have a higher dielectric constant than silicon dioxide. A power amplifier, wherein each of the third capacitors is formed by a PN junction capacitor in the semiconductor substrate, wherein the third capacitor is formed by a capacitor including a dielectric film. 2. The bias diode of the first bias circuit is connected between a base and a collector of an NPN-type sixth transistor of the first bias circuit, and has a collector-emitter path of the sixth transistor. 2. The power amplifier according to claim 1, wherein the power amplifier is connected between the base of the fifth transistor and the output terminal. 3. A base of the third transistor and a base of the fourth transistor are respectively driven by an output signal of a drive stage amplifier formed on the semiconductor substrate, wherein the drive stage amplifier is an NPN-type seventh transistor. A seventh transistor, an emitter-grounded NPN-type eighth transistor whose base is Darlington-connected to the emitter of the seventh transistor, and a transistor connected between the base of the seventh transistor and the collector of the eighth transistor. And a fourth capacitor that has been selected.
A power amplifier according to claim 1. 4. The semiconductor substrate has a differentially connected N
A voltage follower circuit including PN-type ninth and tenth transistors, and a load resistor connected between the collector of the ninth transistor and the first operating potential point; The output signal of the driving stage amplifier is transmitted to the base of the ninth transistor of the voltage follower circuit,
The third transistor operates as a collector load of the tenth transistor, and the collector and the base of the tenth transistor are short-circuited.
The power amplifier according to any one of claims 1 to 3, wherein the tenth transistor and the tenth transistor operate as a voltage follower. 5. The driving stage amplifier further comprises a second bias circuit connected to the collector of the eighth transistor and load means, wherein the driving stage amplifier appears at the collector of the eighth transistor. The power amplifier according to claim 4, wherein an output signal is transmitted to a base of a ninth transistor of the voltage follower circuit via the second bias circuit. 6. The NPN eleventh bias circuit, wherein the second bias circuit has an emitter connected to a collector of the eighth transistor and a collector connected to a base of the ninth transistor of the voltage follower circuit. A transistor, a first resistor connected between the base of the eleventh transistor and the load means, a second resistor connected between the base and the emitter of the eleventh transistor, The power amplifier according to claim 4 or 5, further comprising a third resistor connected between a collector of the eleventh transistor and the load means. 7. The output signal of the drive stage amplifier appearing at the collector of the eighth transistor is transmitted to the base of the fourth transistor via a resistor. A power amplifier according to any one of the above. 8. The power amplifier according to claim 1, wherein the high-dielectric-constant dielectric films of the first capacitor and the second capacitor are made of silicon nitride.