Audio power amplifier
AssigneeSGS-Thomson Microelectronics S.A.
InventorsEdoardo Botti, Claudio Tavazzani
Life of this patent
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Abstract
An amplifier comprising a power stage the output of which is compared with a reference level by a comparator. If the output exceeds the reference level, a reduction is made in the gain of a variable-gain cell upstream from the power stage. The reference level varies with temperature, and, more specifically, presents a high constant value (e.g., greater than the supply voltage) when temperature is below a predetermined threshold (e.g., 130.degree. C.), and decreases in proportion to an increase in temperature, when the temperature exceeds the predetermined threshold. Thus, the input signal is only attenuated in the event the output signal exceeds given values inversely proportional to temperature, and with no reduction in peak output at high temperature.
Claims18
A power amplifier comprising:
- a variable-gain element having a gain control terminal;
- an amplifying stage cascade connected to said variable-gain element and having an output supplying an output signal;
- comparing means for comparing amplitudes having a first input connected to said amplifying stage, and an output connected to said control terminal, said comparing means having a second input connected to said output of said amplifying stage and receiving said output signal and a third input receiving a second electric reference quantity varying with temperature;
- and
- a variable generating means for generating an electric reference quantity the amplitude of which varies with temperature, said generating means being connected to said first input of said comparing means, said first and second electric reference quantities defining the maximum and minimum permitted level of said output signal.
A power amplifier providing an output signal with thermal overload protection, comprising:
- a variable gain amplifier stage having an input terminal receiving an input signal, a variable gain output terminal, and a control terminal controlling the gain of said variable gain amplifier stage;
- an amplifying stage with an amplifier input terminal coupled to said variable gain output terminal and generating the output signal for the power amplifier;
- and
- a comparator receiving the output signal and generating a control signal coupled to said control terminal to reduce the gain of said variable gain amplifier stage if the amplitude of said output signal exceeds the amplitude of a first reference signal, said first reference signal generated by a reference generator and having an amplitude that varies proportionally with the temperature of the power amplifier, said reference generator generating a second reference signal having an amplitude that varies proportionally with the temperature of the power amplifier, said first and second reference signals defining a maximum and minimum amplitude range, respectively, of said output signal, whereby the amplitude of the output signal of the power amplifier is maintained within said range.
A method of protecting a power amplifier from thermal overload damage, the method comprising the steps of:
- (a) measuring a temperature value of the amplifier using a temperature sensor;
- (b) generating a first reference voltage that varies in proportion to said temperature value;
- (c) generating a second reference voltage that varies in proportion to said temperature value;
- (d) comparing an output voltage from the amplifier to said first and second reference voltages, said first and second reference voltages defining a range of amplitudes of said output voltage;
- and
- (e) varying the amplitude of said output voltage so that the amplitude of said output voltage is maintained within said range.
Dependencies are inferred from the claim text.