JPH0439921B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to the so-called soft-clipping of amplifiers that include transistors that saturate depending on an input signal, for example.

2. Description of the Related Art A bootstrap circuit is used in the final stage amplifier of a battery-powered audio device, and an operation mode is set in which the output transistor is saturated in accordance with an input signal.

Conventionally, in this type of amplifier, by using a PNP type transistor etc. in the driver circuit of the output transistor, the saturation of the output transistor is slowed down by taking advantage of the decrease in the current amplification factor hfe due to the large current flowing near the clip of the output transistor. Soft clipping was achieved using this method.

Problems to be Solved by the Invention In such an amplifier designed for soft clipping, the clipping waveform varies depending on the transistors that make up the driver circuit, making it difficult to obtain a stable clipping output, and making it difficult to obtain audio output. However, there were drawbacks such as a decrease in sound quality and the generation of harmonic components due to clipping, which caused interference with neighboring radio receivers.

Therefore, this invention sacrifices the audio output,
The present invention aims to provide an amplifier that achieves soft clipping while avoiding the effects of radio wave interference on radio receivers, deterioration of sound quality, and variations in drive circuit elements.

Means for Solving the Problems The amplifier of the present invention is provided with a preamplifier (transistors 2, 4 and constant current source 6) that receives and amplifies an input signal, and from this preamplifier, the positive side of the input signal is A first transistor 48 that receives a drive current according to the negative amplitude of the input signal and becomes conductive when the input signal has a positive amplitude, and a second transistor 58 that becomes conductive when the input signal has a negative amplitude are connected in series. The amplifier has a bootstrap circuit between the intermediate connection point of the first and second transistors and the power supply side to take out the amplified output, and the amplifier receives the output of the preamplifier and outputs the amplified output. a third transistor 46 that generates a drive current to the base of the first transistor; and a third transistor 46 that is installed between the third transistor and the base of the first transistor to generate the drive current to the base of the first transistor. a first resistor 60 that allows the current to flow, and a first shunt that shunts the drive current generated by the third transistor to the collector side of the first transistor by forming a bypass with respect to the first resistor. a fourth transistor 50 receiving the output of the preamplifier and generating a drive current to the base of the second transistor;
52, a second resistor 64 installed between the fourth transistor and the base of the second transistor to allow the drive current to flow to the base of the second transistor, and a The present invention is characterized by comprising a second shunt circuit 66 that shunts the generated drive current to the collector side of the second transistor by forming a shunt to the second resistor.

Effect This invention allows a drive current to flow through first and second resistors installed on the base sides of first and second transistors, and a voltage generated in the second and third resistors due to the drive current. Depending on the drop, a portion of the drive current is transferred from the first or second shunt circuit to the first
Alternatively, the saturation state of the first and second transistors is slowly controlled by joining the operating current of the second transistor.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the amplifier of the invention.

In FIG. 1, a differential amplifier consisting of transistors 2 and 4 and a constant current source 6 is installed as a preamplifier at the input section of this amplifier, and between the base of transistor 2 and the ground line, Input terminals 8, 10 are formed to which the input signal V _IN to be applied is applied. A voltage Vcc is applied from the drive power source between the ground side line and the power supply terminal 12 provided on the positive side line, and a resistor 1 is connected as a bias circuit.
A voltage dividing circuit consisting of 4 and 16 circuits is installed. A constant bias voltage formed by voltage division by resistors 14 and 16 is applied to the base of transistor 2 via resistor 18.

Further, a feedback terminal 20 formed at the base of the transistor 4 is connected to a resistor 22 and a capacitor 24.
is connected. A resistor 26 is connected between the base of the transistor 4 and the output point of the amplifier, and a feedback circuit is formed by the resistor 22 connected to the feedback terminal 20, the capacitor 24, and the resistor 26.

The output of this differential amplifier is taken out from the collector side of transistor 4, and transistors 28 and 3
A current mirror circuit consisting of 0 is installed to take out its output. A resistor 32 is connected between the collector of the transistor 30 and the ground line, and also connected between the base and emitter of a transistor 34.

A first resistor 36, a constant current source 38, diodes 40 and 42, and a resistor 44 are connected between the collector of the transistor 34 and the positive line. Transistor 46 as the third transistor
constitutes a drive circuit for the output transistor 48 that is the first transistor, transistors 50 and 52 as the fourth transistor, and a constant current source 5.
4 and the diode 56 constitute a drive circuit for the output transistor 58 as the second transistor.

Emitter of transistor 46 and transistor 4
A first resistor 60 is inserted between the emitter of the transistor 46 and the collector of the transistor 48, and a first resistor 60 is inserted between the emitter of the transistor 46 and the collector of the transistor 48. A first shunt circuit 62 is installed to shunt current to the collector side of the transistor 48 and add it as part of the operating current of the transistor 48 .

A resistor 64 is also connected between the base of the output transistor 58 and the emitter of the transistor 52, and the resistor 64 is connected between the emitter of the transistor 52 and the collector of the transistor 58.
A second shunt circuit 66 is provided which adds a portion of the drive current applied from the transistor 58 to the operating current on the collector side of the transistor 58.

That is, the resistor 60 and the shunt circuit 62 constitute a soft clip circuit that slows the clipping operation of the transistor 48, and the second resistor 64 and the shunt circuit 66 constitute a soft clip circuit that slows the clipping operation of the transistor 58. are doing.

The output transistors 48 and 58 are connected in series between the positive line and the ground line, and output terminals 67 and 68 are formed between the collector and emitter of the output transistor 58. A speaker 70 is connected as a load through the speaker. In addition, a resistor 36 and a constant current source 38,
A bootstrap capacitor 74 is connected between the bootstrap terminal 72 formed at the connection point with the output terminal 67 and the output terminal 67.

The operation of the above configuration will be explained with reference to FIG.

Input signal V _IN applied to input terminals 8 and 10
is amplified by a differential amplifier consisting of transistors 2 and 4 and constant current source 6, and its differential output is applied from transistor 4 to transistor 34 via transistors 28 and 30.

The base current of the transistor 34 increases or decreases depending on its amplified output, and the operations of the transistor 46 and the transistors 50 and 52 are switched depending on the polarity of the input signal, and current flows alternately. Switching is performed alternately depending on the positive and negative amplitudes of the signals of the transistors 48 and 58. The DC base potential of transistors 2 and 4 is set to 1/2 of the power supply voltage Vcc, so the midpoint level of the differential output signal is
It becomes Vcc/2.

When the drive current flowing from the transistor 46 to the base of the transistor 48 becomes large, the transistor 48 becomes saturated, and when the drive current flowing from the transistor 52 to the base of the transistor 58 becomes large, the transistor 58 also becomes saturated, as shown in FIG. As shown by the broken line in A,
This results in a clipping operation in which part of the signal waveform is clipped.

In this circuit, when the drive current flowing from the emitter of the transistor 46 to the base of the transistor 48 increases, the voltage drop occurring across the resistor 60 increases, and when the transistor 48 is saturated, the emitter potential of the transistor 46 drops to the collector of the transistor 48. becomes higher than the potential. Similarly, when the drive current flowing from transistor 52 to the base of transistor 58 increases, the emitter potential of transistor 52 becomes higher than the collector potential of transistor 58 due to the voltage drop across resistor 64.

Therefore, part of the drive current flowing from the transistor 46 flows to the collector side of the transistor 48 via the shunt circuit 62, and flows to the transistor 48 as part of its operating current. Similarly, part of the drive current flows from the emitter of the transistor 52 to the collector side of the transistor 58 via the shunt circuit 66, and flows to the transistor 58 as part of its operating current.

In this way, part of the drive current is transferred to the shunt circuit 6
2, 66 to the operating current of transistors 48, 58, each transistor 48, 58
The clipping operation of the output terminals 67 and 6 becomes slow.
The output voltage waveform applied from the speaker 8 to the speaker 70 has the corners of the clip portion removed, as shown in FIG. 2B, so that soft clipping is achieved.

Here, the base-emitter voltages V _BE46 , V _BE48 , V _BE50 of the transistors 46, 48, 50, the constant current flowing through the constant current source 38, I ₃₈ , the diode 40,
42, 56 forward drop voltage V _F40 , V _F42 , V _F56 ,
Assuming that the resistance values of the resistors 44 and 60 are R ₄₄ and R ₆₀ and the current flowing to the base of the transistor 48 is I _B48 ,
The output voltage V _O appearing at the output terminal 67 is V _O =V _BE48 +I _B48 ·R ₆₀ +V _BE46 −V _F40 −V _F42 −I ₃₈ ·R ₄₄ =V _BE50 −V _F56 .

3 to 7 show specific circuit configuration examples of the shunt circuits 62 and 66, and the same parts as in the embodiment shown in FIG. 1 are given the same reference numerals.

The shunt circuits 62 and 66 shown in FIG. 3 use a transistor 76. In this circuit, the shunt current can be adjusted depending on the control input V _C applied to the control input terminal 78 formed at the base of the transistor 76 . Note that I _D represents the drive current, I _d represents its shunt current, and I _b represents the current flowing to the bases of the transistors 48 and 58.

The shunt circuits 62 and 66 shown in FIG. 4 use a diode-connected transistor 80. When a diode is used in this way, no external control is required, and its forward drop voltage V _F
Soft clipping can be started by setting the threshold level to 0, and its logarithmic compression can be realized.

The shunt circuits 62 and 66 shown in FIG.
It is composed only of In this circuit, the current limiting effect of the resistor 82 is obtained.

The shunt circuits 62 and 66 shown in FIG. 6 use a diode 84 and a resistor 86, and the fourth
The characteristics of both the shunt circuits 62 and 66 shown in FIG. 5 and FIG. 5 can be utilized.

The shunt circuits 62 and 66 shown in FIG. 7 use a capacitor 88 and a resistor 90. A circuit including such a capacitor 88 is provided with filter characteristics and can improve frequency characteristics.

FIG. 8 shows the shunt circuit 6 shown in FIGS. 4 to 6.
2,66, where A is composed only of a diode consisting of a transistor 80 shown in Fig. 4, and B ₁ and B ₂ are composed only of a resistor 82 shown in Fig. 5. , C indicate the case using the diode 84 and resistor 86 shown in FIG. 6, respectively, and V _F indicates the forward voltage drop of the diode.

That is, in characteristic A, soft clipping starts from the point exceeding the forward drop voltage V _F and logarithmic compression is realized, and in characteristics B ₁ and B ₂ , only the current limiting action of resistor 82 occurs, so that resistors 60 and 64 Linear soft clipping can be obtained from the relationship with the voltage drop of
The slopes of the characteristics B ₁ , B _{2 ,} etc. can be changed depending on the resistance value of the resistor 82 . Further, in characteristic C, both characteristics are combined, and ideal soft clipping is realized. For characteristics B ₁ , B ₂ , and C, as the resistors 60 and 64 become larger, the degree of soft clipping increases, but since the drive ability of the transistors 48 and 58 tends to be insufficient, the optimum value is determined by experiment. find the point.

In addition, FIG. 9 shows the shunt circuits 62 and 6 shown in FIG.
Characteristics are shown in soft clipping of 6. In the shunt circuits 62 and 66 shown in FIG. 7, the capacitor 88 and the resistor 90 constitute a differentiating circuit, so that a differentiating effect can be obtained. That is, in the shunt circuits 62 and 66 shown in FIGS. 3 to 6, the leading and trailing edges of the waveform have slow corners, whereas as shown in FIG. only slows down.

Effects of the Invention As explained above, according to the present invention, it is possible to realize ideal soft clipping without sacrificing output, and it is possible to suppress the deterioration in sound quality caused by clipping and improve the audio quality. As well as being able to
It is possible to suppress the generation of harmonic components, and it is also possible to correct non-uniformity in clipping due to the influence of the current amplification factor of the element.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the amplifier of the present invention, FIG. 2 is an explanatory diagram showing its operating waveforms, and FIGS. 3 to 7 are circuit diagrams showing specific circuit configuration examples of a shunt circuit. FIG. 8 is an explanatory diagram showing its operating characteristics, and FIG. 9 is an explanatory diagram showing operating waveforms of the shunt circuit shown in FIG. 7. 2, 4...transistor (preamplifier), 6...
... constant current source (preamplifier), 46 ... third transistor, 48 ... output transistor (first transistor), 50, 52 ... fourth transistor, 58 ... output transistor (second transistor) ), 60... first resistor, 62... first shunt circuit, 64... second resistor, 66... second shunt circuit, 74... capacitor, 76... transistor, 80... transistor (diode), 8
2...Resistance.

Claims (1)

[Claims] 1. A preamplifier that receives and amplifies an input signal is installed, receives a drive current from the preamplifier according to the positive and negative amplitudes of the input signal, and amplifies the positive side of the input signal. A first transistor that becomes conductive at an amplitude and a second transistor that becomes conductive at a negative amplitude of the input signal are connected in series, and an intermediate connection point between these first and second transistors is connected to a power supply side. a third transistor that receives the output of the preamplifier and generates a drive current to the base of the first transistor; a first transistor disposed between the transistor and the base of the first transistor to allow the drive current to flow through the base of the first transistor.
a first shunt circuit that shunts the drive current generated by the third transistor to the collector side of the first transistor by forming a bypass with respect to the first resistor; a fourth transistor that receives the output of the preamplifier and generates a drive current to the base of the second transistor; and a fourth transistor that is installed between the fourth transistor and the base of the second transistor to generate the drive current. is applied to the base of the second transistor.
a second shunt circuit that shunts the drive current generated by the fourth transistor to the collector side of the second transistor by forming a bypass with respect to the second resistor; An amplifier characterized by: 2. The amplifier according to claim 1, wherein the first and second shunt circuits are composed of transistors. 3. The amplifier according to claim 1, wherein the first and second shunt circuits include diodes.