JPH0964657A - Push-pull power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a signal stage power amplifier consisting only of a power amplification element capable of inputting a signal on the basis of ground without using input and output transformers and having voltage amplification gain in a signal ended push-pull power amplifier consisting of as complementary power amplification element. SOLUTION: An emitter or source grounding type complementary signal ended push-pull power amplifier circuit and a floating power supply insulated from ground are combined and power is supplied to a load connected between the potential intermediate point of the floating power supply and the ground. Consequently, audio power amplification having high faithfulness can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier for amplifying an audio signal and supplying power to a vibration element such as a speaker or a piezoelectric element.

[0002]

2. Description of the Related Art In an audio power amplifier, a so-called push-pull amplifier circuit is used to reduce second-order harmonic distortion while reducing power loss when there is no signal.
In push-pull amplifiers that use semiconductors of bipolar transistors and FETs as power amplification elements, balanced push-pull circuits that use input and output transformers may be used for simple applications, but for the purpose of high fidelity In most cases, the single-ended push-pull circuit that eliminates the need for an output transformer by using a complementary pair is adopted.

For the purpose of reducing distortion and suppressing output impedance to improve the braking ability to the speaker, most of them employ an emitter follower or source follower output system in which a large amount of local negative feedback is added, but these have a voltage gain. Since I do not have it, some kind of voltage amplification means is necessary. If an input transformer is used, no active element is required, but since the input transformer deteriorates the frequency characteristic, today, the role of voltage amplification is shared by the drive circuit with an active element in front. This drive amplification stage normally has two stages, and it is customary to provide negative feedback to the entire amplifier on that stage.

Some of them dislike the emitter follower or source follower output system, avoid the local negative feedback at the final stage, and adopt the grounded emitter collector output or grounded source drain output system, but at least one preamplifier is used. It is always arranged.

[0005]

In a general emitter follower or source follower output system, a large amount of final stage local negative feedback and multistage negative feedback impair the stability of the entire amplifier and deteriorate the transient characteristics. The current situation is that adverse effects such as loss of the auditory sense of reality in audio reproduction are regarded as problems.

In view of this problem, some of the grounded-emitter or source-grounded output systems, which are partially adopted,
When the output section is included, the minimum number of amplification stages is two, and the stability during negative feedback cannot be said to be perfect. Further, it is widely recognized that the smaller the number of amplification stages is, the better for high fidelity reproduction, and it is doubtless that it is the best if it is possible to construct a one-stage amplifier using only power elements.

However, if an attempt is made to construct a complementary single ended push-pull power amplifier circuit with only one stage, as long as a normal power source with the zero potential point grounded is used, the emitter or source of both push-pull power elements is positive or negative. There is no choice but to place it at the power supply end.

Therefore, unless an input transformer is used to convert the signal reference point, ripples and other noises and fluctuations in the positive and negative power supply lines will occur at the base or gate of the element with respect to the input signal that enters with reference to the ground. It will be mixed and weighted to the net input signal. However, when this is disliked and an input transformer is used, frequency distortion is generated.

The present invention has been made in view of the above circumstances, and provides a power amplifier having a necessary minimum amount of amplifying elements to provide a minimum necessary negative feedback, thereby providing a high fidelity. It aims to realize audio power amplification with a certain degree.

[0010]

The means of claim 1 will be described with reference to the drawings.

FIG. 1 is a principle configuration diagram in accordance with a single ended push-pull amplifier (P) using power MOS FETs (U1, U2) forming a complementary pair.

The sources of U1 and U2 are grounded, appropriate DC biases (Eg1 and Eg2) are applied to the gates, and a common AC signal (ei) with respect to the ground is input thereto.

The positive and negative B power supplies (Ecc, Eee) are insulated with a sufficient impedance with respect to the ground, the positive voltage end is the drain of the N-channel FET (U1), and the negative voltage end is the drain of the P-channel FET (U2). Connected.

The load (RL) is a zero potential point (E
0) and ground. The above is the basic configuration of the push-pull power amplifier of claim 1.

FIG. 2 is a more practical configuration diagram according to the single-ended push-pull amplifier (Q) using the bipolar transistors (V1, V2) forming a complementary pair.

Each emitter has a small resistor (R
e) is inserted and grounded via a small common resistor (Rf) for negative current feedback in order to further increase the input impedance. A DC bias is applied to the base from an independent small power source (Eb) through a voltage dividing resistor to supply base bias currents (Ib1, Ib2) to which a common input AC signal ei is applied.

Floating power supply Ec isolated from the ground
As in FIG. 1, c and Eee are connected to both collectors, and the load RL is connected between the zero potential point E0 of the power supply and the ground. The above is the description of the means of claim 1.

[0018]

The operation of the push-pull power amplifier according to claim 1 will be described with reference to FIG.

Power MO forming a complementary pair
An input signal ei to the gate is applied to both drains of the S-FET.
With a value corresponding to the transconductance gm of the element and the element, the AC output current (io1,
io2) appears, and this is supplied to the positive and negative power supply terminals connected to both drains forming the same point in terms of alternating current.

Since the power supplies Ecc and Eee are insulated from the ground connected to the source and are in a floating state, both drain currents io1 and io2 flow from the power supply zero potential point E0 to the load RL connected to the ground. (Io1 + io
2) An output voltage eo having a polarity opposite to that of ei of RL appears at the power supply zero potential point E0 which is regarded as the output terminal.

Therefore, the load is eo (io1 + io2)
AC power is supplied. Thus, without using an input transformer, a single-source push-pull power amplifier of only a pair of complementary power amplifier elements of a source-grounded amplification system having a voltage gain is realized while using ground as a signal input reference.

[0022]

Embodiments will be described with reference to the drawings.

FIG. 3 shows an embodiment of a power amplifier (R) which uses the complementary pairs U1 and U2 of the power MOS FETs as the power amplifying element to realize the invention of claim 1.

The floating power supplies Ecc and Eee are composed of a power supply transformer (T) and a capacitor input rectification circuit (D), and are connected to both complementary elements.

A gate bias voltage Eg1 or Eg2 is supplied to both elements by using an independent small power source Eb and a resistance voltage divider circuit, an appropriate idling current to be operated as a class AB amplifier circuit is set, and the source is grounded. Configure a push-pull power amplifier circuit.

The load RL is connected between the power source zero potential point E0 and the common source point of both elements, and the drain output currents io1 and io2 are supplied to it according to the principle of FIG.

Between the power source zero potential point E0 and the common source point, the voltage is divided by resistors R1 and R2, which are relatively larger than RL, and the divided point is grounded. R1 on the source side is selected to be sufficiently smaller than R2 to maintain the voltage gain of the source-grounded amplifier circuit. As a result, a part of the output voltage eo generated in the load RL, that is, a voltage having a value of eo.R1 / (R1 + R2) is negatively fed back to the input side, thereby increasing the input impedance and decreasing the output impedance.

By selecting balanced complementary amplifier elements U1 and U2 and setting an appropriate idling current, it is possible to have a sufficiently low distortion characteristic as an audio power amplifier, and by applying an appropriate negative feedback, Good braking characteristics can be maintained even for loaded speakers. The above is the embodiment of the single-ended push-pull amplifier according to the invention of claim 1.

[0029]

By adopting the means of the present invention, the input signal coming into the ground reference is amplified as it is by the source grounded or grounded emitter amplifier circuit without relying on the input transformer, and a single stage number is sufficient. Power to the load,
An extremely simple audio power amplifier can be constructed.

In contrast to the multi-stage intensity negative feedback in a general amplifier, which impairs the stability of the entire amplifier,
The power amplifier according to the present invention comprises a power amplifier with a minimum required number of amplifying elements, provides a power amplifier with extremely stable minimum required negative feedback, and provides audio power amplification with a high degree of fidelity. To realize.

Since the number of amplification stages is one, the information loss and the transforming effect on the input signal can be suppressed to a very small level, and an audio reproducing amplifier excellent in audibility can be produced.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of claim 1;

FIG. 2 is a diagram showing a practical configuration of claim 1 using a bipolar transistor.

FIG. 3 is a diagram showing an embodiment of claim 1 using a power MOS • FET.

[Explanation of symbols]

D Rectifier circuit E0 Power supply zero potential point Eb Small power supply Ecc Positive power supply Eee Negative power supply Eg1 Gate bias voltage Eg2 Gate bias voltage ei AC input signal eo AC output voltage Ib1 Base bias current Ib2 Base bias current io1 AC output current io2 AC output current P Complementary single-ended push-pull power amplifier circuit Q Complementary single-ended push-pull power amplifier circuit with bipolar transistor R Complementary single-ended push-pull power amplifier circuit with power MOS / FET R1 Voltage feedback resistor R2 min Pressure resistance Re Micro resistance Rf Current feedback resistance RL Load T Power transformer U1 N-channel MOS / FET amplification element U2 P-channel MOS / FET amplification element V1 NPN transistor amplification element V2 PNP transistor amplification element 1 Input terminal 2 Output terminal

Claims (1)

[Claims] 1. A complementary power amplifier element (U1 / U).
(2, V1 / V2) Both emitters or sources are grounded directly or through a small resistance, the same AC signal is input to both bases or gates, and AC outputs are taken from both AC shorted collectors or drains. So-called complementary single ended push-pull power amplifier circuits (P, Q, R) and floating positive and negative power supplies (Ecc, Ee) in which the zero potential point (E0) is insulated with a sufficiently large impedance with respect to ground.
e), the positive voltage end is connected to the collector of the NPN transistor or the drain of the N-channel FET, and the negative voltage end is connected to the collector of the PNP transistor or the drain of the P-channel FET. A push-pull power amplifier that outputs power to a load (RL) connected to ground or to E0 and the emitter or source of the device.