JPH01189211A - Power amplifier - Google Patents

Abstract

PURPOSE:To reduce a distortion due to the non-linearity of an output transistor(TRS) by adding a voltage proportionate to the fluctuation components of voltages between the bases and emitters of first and second output transistors to the base voltages of first and second driving TRSs, and canceling the above-mentioned fluctuation components. CONSTITUTION:Current mirror circuits 6a and 6b have a k-fold transmission ratio by the constant settings of resistances 4a, 5a, 4b and 5b. TRSs 2a and 2b and the collectors 7a and 7b are connected, emitters are mutually connected through resistances 8a and 8b (R3), simultaneously, the bases are connected to the bases of driving TRSs Q3 and 4, and the collectors of the TRSs 3a and 3b are mutually connected. The midpoint of an emitter resistance r1 of output TRSs Q1 and Q2 and parallel resistances 9a and 9b (r2) is connected to the midpoint of the resistances 8a and 8b, on the other hand, the midpoint of resistances 10a and 10b (R4) parallel to the resistances 8a and 8b is connected to the collectors of the 3a and 3b and, simultaneously, through resistances 11a and 11b (R2) to the bases of the 7a and 7b, respectively, and resistances 12a and 12b (R1) are connected between the bases and the emitters of driving TRSs Q5 and 6. When each constant made into KR1R4=(r2+R3){(1+K)R2+R4} is established, a power amplification without distortion components can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention particularly relates to a power amplifier in which distortion due to nonlinearity of an output transistor is reduced.

[Prior Art] Conventionally, power amplifiers for audio use have been known that perform class A operation when a signal is small and perform B drive operation when a large signal occurs, but the output stage thereof has a configuration as shown in FIG. Overcome.

A third positive-side drive transistor Q5, a first drive transistor Q3, and a first output transistor Q1 are connected in multiple stages in Darlington, a fourth negative-side drive transistor Q6 is connected in multiple stages in Darlington, and a second drive transistor Q4. and a second output transistor Q2, the emitters of the first and second output transistors Q1 and Q2 are connected via first and second emitter resistors r and r connected in series, and , the middle point of the connection between the second emitter resistors r and r is connected to the load R[ as an output terminal, and the third
, a fourth drive transistor Q5, and a first drive transistor Q5 at the base of QB.
, second bias voltages VB and VB are applied.

[Problems to be Solved by the Invention] In the class AB operation region of the above power amplifier, the base-emitter voltage VBE of the first and second output transistors Q1 and Q2 is non-linear with respect to the current, Furthermore, since the current change is much larger than that of other drive transistors, the first and second output transistors Q1 and Q2 generate large distortions due to their nonlinearity.

Hereinafter, the problems to be solved by the present invention will be clarified using a circuit analysis method.

The equivalent circuit of the first and second output transistors Q1 and Q2 is as shown in FIG.
The base-emitter voltage VBE of the second output transistors Q1 and Q2, the fluctuation components (non-linear components) Dl, D of the emitter internal resistance re and the base-emitter voltage VBE
2, the equivalent circuit of the conventional example shown in FIG. 7 can be expressed as shown in FIG.
It is equivalent to a diagram.

Here, Dl: Variation component of the base-emitter voltage VBE of the first output transistor Q1 D2: Variation component of the base-emitter voltage VBE of the second output transistor Q2 Element e: First and second output transistors Emitter internal resistance 3VBE of Q1, Q2: Sum of base-emitter voltages VBE of third drive transistor Q5, first drive transistor Q3, and first output transistor Q1 Fourth drive transistor Q6, second drive transistor The sum r of the base-emitter voltage VBE of Q4 and the second output transistor Q2: the voltage of the first and second emitter resistors VS.

In the class A operation region, the output voltage ■O is as follows from Figure 10: 2RL RL VO= -Vs+ -(old +02)re+r+2R
L re+r+2RL.

In this equation, the first term is the undistorted signal component, and the second term is the distortion based on the fluctuation components [)1 and [)2 of the base-emitter voltage VBE of the first and second output transistors Q1 and Q2. It is an ingredient.

Next, if we consider the class B operating region (for example, when the second output transistor Q2 is OFF), its equivalent circuit becomes as shown in Fig. 11, and similarly, its output voltage ■O is RL RL VO= -Vs+ -[)1 re+r+2RL re+r+2RL
becomes.

In this equation, the first term is a non-distorted signal component, and the second term is a distortion component based on the fluctuation component D1 of the base-emitter voltage VBE of the first output transistor Q1.

In this manner, the conventional power amplifier generates large distortion due to the nonlinearity of the first and second output transistors Q1 and Q2, and this distortion component is included in the output voltage.

[Means for Solving the Problems] The present invention comprises: a positive-side third drive transistor Q5, a first drive transistor Q3, and a first output transistor Q1 connected in multiple stages to Darlington; negative-side connected in multiple stages to Darlington. The first and second emitters include a fourth drive transistor Q6, a second drive transistor Q4, and a second output transistor Q2, and the emitters of the first and second output transistors Q1 and Q2 are connected in series. resistance r1,
These first and second emitter resistors r
In a configuration in which the connection midpoint of 1 and rl is connected to the load R[ as an output terminal, and the first and second bias voltages VB and VB are applied to the bases of the third and fourth drive transistors Q5 and Q6, respectively. , a voltage proportional to the fluctuation components D1 and D2 of the base-emitter voltage VBE of the first and second output transistors Q1 and Q2 is added to the base voltage of the first and second drive transistors Q3 and Q4. The present invention is characterized in that the fluctuation components D1 and D2 of the first and second output transistors Q1 and Q2 are canceled.

[Function] Below, in FIG. 1 showing a typical embodiment of the present invention,
The effect will be explained using a circuit analysis method.

Regarding the first and second output transistors Q1 and Q2, their equivalent circuits can be expressed using the same concept as that in FIG.
In the class A operating region, the situation is as shown in FIG.

Here, Dl: Variation component of the base-emitter voltage VBE of the first output transistor Q1 D2: Variation component of the base-emitter voltage VBE of the second output transistor Q2 Element e: First and second output transistors Emitter internal resistance VS of Q1 and Q2 Two-power voltage Vl: Base voltage V2 of the first and second drive transistors Q3 and Q4: Emitter voltage of the fifth and sixth transistors 7a and 7b vo': First and second output transistors Q1, Q2
emitter voltage IO = output (load) current C: collector current of the first and third transistors on the input side of the first and second current mirror circuits 5a and 5b KIc: current of the first and second transistors Mirror circuits 6a, 6b
Collector current rl of the second and fourth transistors on the output side: First and second emitter resistances R1: Thirteenth and fourteenth resistances R2: Eleventh and twelfth resistances R3: Fifth and sixth Resistance R4: 9th and 10th resistance r2: 7th and 8th resistance Rlo: R1/2 R2°: R2/2 R3': (R3+r2)/2 R4°: R4/2.

In FIG. 1, fifth and sixth transistors 7a and 7b
The current change in the first and second output transistors Q1 and Q2
The change in the base-emitter voltage VBE is also small.

Therefore, considering the signal components, in FIG. 2, the base voltage 1 of the first and second drive transistors Q3 and Q4 and the emitter voltage v2 of the fifth and sixth transistors 7a and 7b are V2 = V1 It is.

In addition, in general, the first and second output transistors Q1, Q
2 emitter current 11 and the fifth and sixth transistors 7
a, 7b emitter voltage V2 - the emitter voltage VO° of the first and second output transistors Q1 and Q2 (i.e., the current that flows due to the potential difference between the emitter voltages VO° of the first and second output transistors Q1 and Q2 (that is, due to the fluctuation components D1 and D2 of the first and second output transistors Q1 and Q2) The relationship between the flowing current) I3 is 11)■3, so it is thought that 10μ11.

Under the above conditions, in the class A operating region, the first,
Emitter voltage VO of second output transistors Q1 and Q2
° is 2R3'RL' ((1+K)R2°+R4°)vo
'=□・Vs R3°(re+2RL')((1+K)R2°+R4
°)-KreR1°R4°RL'[KR1°R4'
-R3°((1+K)R2°+R4°)1R3°(re
+2RL') ((1+)r12°+R4')-r
eR1°R4°・([11+D2) However, RL' = rl/2 + RL.

Therefore, R1°R4°=R3°((1+K)R2°+R4'
) That is, KRIR4= (r2+R3) ((1000K) R2+R4
), by setting each constant, vO"=VS.

Therefore, RL yo-□・VS rl+2RL , and the output voltage VO does not include the fluctuation components D1 and D2, and the impedance (r
The effect of e/2> also does not appear on the output voltage VO.

Next, in the B drive operation region (for example, when the second output transistor Q2 is OFF), the equivalent circuit can be shown as shown in FIG.

This equivalent circuit differs from the one in FIG. 2 only in some of the constants of each part, and similarly, the emitter voltages of the first and second output transistors Q1 and Q2 are expressed as °= [3"((1+K)R2°+R4
°) That is, RIR4= (r2+I?3)((1000K)R2+1
4), RL ■O=□・ys rl +2RL, and the output voltage vO does not include the distortion component terms D1 and D2. Also, the impedance rl between (a) and (b) in Figure 3
The influence of 10r2 does not appear on the output voltage .O.

As described above, in the present invention, the transfer characteristics are the same in both the class A operation region and the B drive operation region, and the base-emitter voltage VBE of the first and second output transistors Q1 and Q2 is non-linear. It is possible to perform faithful power amplification without distortion components by canceling the distortion components caused by the distortion.

[Example] This will be explained with reference to the drawings from FIG. 1 onwards. In the figure, parts equivalent to those of the conventional example shown in FIG. 7 are given the same reference numerals, and their explanations will be omitted.

First embodiment: first and second transistors 2a whose bases are connected together,
The emitter of 3a is connected to the positive power supply 1a via first and second resistors 4a and 5a, and the base and collector of the first transistor 2a are connected to form a first current mirror circuit 6a. Similarly, the emitters of the third and fourth transistors 2b and 3b whose bases are connected to each other are connected to the negative side power supply 1b through the third and fourth resistors 4b and 5b.
and the third transistor 2b.
A second current mirror circuit 6b is configured by connecting the base and collector of the .

Here, first and second current mirror circuits 6a.

6b is the first and second resistor 4a, 5a, third and fourth resistor.
The transmission ratio is doubled by setting the constants of the resistors 4b and 5b.As another example, taking the first current mirror circuit 6a as an example, as shown in FIG.
For a series circuit of a first resistor 4a and a first transistor 2a, a second resistor 5a having the same resistance value as the first resistor 4a and a second transistor 3a having the same specifications as the first transistor 2a. A configuration in which 2 series circuits are connected in parallel, or, as shown in FIG. Resistors 5a, 5a,...
It is also possible to connect them in parallel to approximately double the transmission ratio.

The collectors of the first and third transistors 2a and 2b are connected to the collectors of the fifth and sixth transistors 7a and 7b, respectively, and the emitters of the fifth and sixth resistors 8a and 8b are connected in series. Both values are connected via R3>, and the fifth and sixth transistors 7a17
The base of b is connected to the first and second drive transistors Q3.
, Q4, respectively. In addition, the second above,
The collectors of the fourth transistors 3a and 3b are connected together.

Then, the first and second emitter resistors r connected in series are
1, seventh and eighth resistors 9a connected in series in parallel with rl;
9b (all resistance values are r2), and the connection midpoint thereof is connected to the connection midpoint of the fifth and sixth resistors 8a and 8b connected in series.

On the other hand, the ninth and tenth resistors 1Qa and 10b are connected in series in parallel with the fifth and sixth resistors 8a and 8b connected in series.
(all resistance values are R4), and the connection midpoints are connected to the collectors of the second and fourth transistors 3a and 3b, and eleventh and twelfth resistors 11a and 11b (resistance values are Both are connected to the bases of the fifth and sixth transistors 7a and 7b via R2), and the bases of the fifth and sixth transistors 7a and 7b and the third and fourth drive transistors Q5 , Q6, and the 13th and 14th resistors 12a and 12b (both have a resistance value of R1) are connected respectively.

Then, as mentioned in the [Effect] section, R1' R4
°= R3° ((1+K)R2'+l?4°) That is, KRIR4= (r2+R3)[1+K)R2+R4)
Set each constant so that

Second example: FIG. 6 shows another embodiment.

In this embodiment, first and second current mirror circuits 6a, 6
In b, the first and second resistors 4a and 5a have the same resistance value, and the third and fourth resistors 4b and 5b have the same resistance value, k=1 R1=R3+r2 R2=arbitrary R4= ■ This satisfies the condition.

Furthermore, in this embodiment, by connecting the fifteenth resistor 13 in parallel with the fifth and sixth resistors 8a18b connected in series, the bias currents of the fifth and sixth transistors 7a and 7b are increased. Since the current fluctuations of the fifth and sixth transistors 7a and 7b during load can be relatively reduced, the fifth and sixth transistors 7a
, 7b can be further reduced.

[Effects of the Invention] The present invention has the same transfer characteristics in both the class A operation region and the B drive operation region, and eliminates distortion components due to the nonlinearity of the first and second output transistors Q1 and Q2. Cancellation allows faithful power amplification without distortion components.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the power amplifier of the present invention, FIGS. 2 and 3 are diagrams showing the equivalent circuit, and FIGS. 4 and 5 are diagrams showing the equivalent circuit.
6 is a diagram showing the configuration of another example of the current mirror circuit, FIG. 7 is a diagram showing the configuration of a conventional power amplifier, and FIGS. FIG. 11 is a diagram showing an equivalent circuit. 1a... Positive side power supply, 1b... Negative side power supply, 2a... First transistor, 3a...
...Second transistor, 2b...Third transistor, 3b...Fourth transistor, 4a
...First resistor, 5a...Second resistor, 4b...Third resistor, 5b...Fourth resistor
resistance, 6a...first current mirror circuit,
6b... Second current mirror circuit, 7a...
...Fifth transistor, 7b...Sixth transistor, 8a...Fifth resistor, 8b...
...Sixth resistor, 9a...Seventh resistor, 9
b...8th resistor, 10a...9th resistor, 10b...10th resistor, 11a...
...11th resistor, 11b...12th resistor, 12a...13th resistor, 12b...
・14th resistor, 13...15th resistor, Ql
...First output transistor, Q2...
・Second output transistor, Q3...First drive transistor, Q4...Second drive transistor, Q5...Third drive transistor, Q6
...Fourth drive transistor, rl...
・First and second emitter resistors. Patent Applicant: Onkyo Corporation

Claims (1)

[Claims] A positive third drive transistor (Q5), a first drive transistor (Q3), and a first output transistor (Q1) connected in multiple stages to Darlington, and a fourth negative drive transistor (Q6) connected in multiple stages to Darlington. ), a second drive transistor (Q4), and a second output transistor (Q2), and the emitters of the first and second output transistors (Q1) and (Q2) are connected in series. The first and second emitter resistors (r1), (
r1) is connected to the load (RL) as an output terminal, and the third and fourth drive transistors (Q5) and (Q
6) The first and second bias voltages (VB), (
In the configuration in which VB) is applied, a voltage proportional to the fluctuation components (D1) and (D2) of the base-emitter voltage VBE of the first and second output transistors (Q1) and (Q2) is applied to the first and second output transistors (Q1) and (Q2), respectively. , the second drive transistor (Q3
), (Q4) is added to the base voltage of the above fluctuation component (
A power amplifier characterized in that D1) and (D2) are canceled.