Amplifiers – With control of power supply or bias voltage – With control of input electrode or gain control electrode bias
Patent
1999-02-08
2000-12-19
Mottola, Steven J.
Amplifiers
With control of power supply or bias voltage
With control of input electrode or gain control electrode bias
330140, H03G 320
Patent
active
061632120
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a power amplifier system for use in numerous kinds of audio equipment.
BACKGROUND OF THE INVENTION
An example of a power amplifier system of the prior art is described by referring to FIG. 11. A signal fed in an input terminal 1 passes through a voltage-controlled amplifier 2, and drives a speaker 6, after it is amplified by a power amplifier system 9 comprising a negative feedback circuit 4, a voltage amplifier 3 and a power amplifier 5. In order to prevent the speaker 6 from being input with an excessive power or to avoid a distorted sound due to a wave form being electrically clipped by exceeding a dynamic range, a limiter means has been used in the past, which detects an output of the voltage-controlled amplifier 2, e.g. an input voltage of the power amplifier system 9, converts it into a pulse wave by a voltage comparator 7, converts the voltage into a d.c. signal by integrating it with an integrating circuit 8, and reduces an amplification factor of the voltage-controlled amplifier 2, so as to suppress a wave form distortion of the output.
However, since the composition of the prior art detects and controls only a magnitude of the input signal, it has been unable to control clipping within the power amplifier system 9 itself or clipping at an output stage caused by fluctuation of the power supply voltage, so as to result in a problem of generating a distortion from the speaker.
SUMMARY OF THE INVENTION
A power amplifier system of the present invention is composed of a limiter means that detects a voltage at a point of connection between a voltage amplifier and a power amplifier, and controls a voltage-controlled amplifier by using the voltage. With an adoption of the above structure, clipping of the signal is prevented due to a magnitude of the input signal, fluctuation of the power supply voltage, etc.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram depicting a power amplifier system of a first exemplary embodiment of the present invention;
FIG. 2 is a circuit diagram depicting a voltage comparator constituting a limiter circuit of the same system;
FIG. 3A and FIG. 3B is a drawing showing waveforms of an input voltage and an output voltage of the same voltage comparator;
FIG. 4 is a characteristic chart showing a power supply voltage versus a distortion factor of the output voltage for the same system and a comparison example;
FIG. 5 is a block diagram depicting a power amplifier system of a second exemplary embodiment of the present invention;
FIG. 6 is a circuit diagram depicting a voltage comparator of the same system;
FIG. 7 is a block diagram depicting a power amplifier system of a third exemplary embodiment of the present invention;
FIG. 8 is a block diagram depicting a power amplifier system of a fourth exemplary embodiment of the present invention;
FIG. 9 is a block diagram depicting a power amplifier system of a fifth exemplary embodiment of the present invention;
FIG. 10 is a block diagram depicting another example of the same system of FIG. 9; and,
FIG. 11 is a block diagram depicting a power amplifier system of the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Exemplary Embodiment
FIG. 1 is a block diagram depicting a structure of a limiter circuit of a power amplifier system of a first exemplary embodiment of the present invention. In FIG. 1, a signal supplied to an input terminal 1 is fed to a voltage-controlled amplifier 2, wherein amplitude is limited. An output of the voltage-controlled amplifier 2 is connected to a voltage amplifier 3 at a first stage of the power amplifier system 9. This voltage amplifier 3 is also applied with a voltage fed-back from an output of the power amplifier 5 through a negative feedback circuit 4. An output of the voltage amplifier 3 is connected to the power amplifier 5, and its output power drives a speaker 6. Since a connecting point of the voltage amplifier 3 and the power amplifier 5 is situated within a negative feedback loop of the negative feedback cir
REFERENCES:
patent: 5168148 (1992-12-01), Giebel
patent: 5432473 (1995-07-01), Mattila et al.
patent: 5589796 (1996-12-01), Alberth et al.
Search report corresponding to application No. PCT/JP98/02880 dated Sep. 29, 1998.
English translation of Form PCT/ISA/210.
Matsushita Electric - Industrial Co., Ltd.
Mottola Steven J.
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