Amplifier calibration apparatus and method therefor

A method for automatically calibrating an amplifier contained in an audio device, the amplifier comprising a digital potentiometer having a digital control, an input and a corresponding output, the digital control having value within an operating range indicative of the gain of the amplifier, the method comprising the steps of:

• a) generating a test signal using a signal generator located within the audio device as directed by a processor device located within the audio device;
• b) scaling the test signal in the digital potentiometer to obtain an scaled test signal;
• c) comparing the scaled test signal to a constant signal in a comparator circuit located within the audio device;
• d) indicating any difference between the scaled test signal and the constant signal to the processor device;
• e) altering the value of a digital control word operably fed into the digital control potentiometer in response to an indicated difference;
• and
• f) repeating steps (a) through (e) until the difference between the current value of the digital control word and the previous value of the digital control word equals one.

An amplifier calibration apparatus comprising:

• means for amplifying a signal, said amplifying means having a control, an input and a corresponding output, said control serving to set the gain of said signal between said input and said corresponding output;
• means for setting a set point for said amplifying means, said set point corresponding to a zero gain between said input and said corresponding output, said set point being operably asserted upon said control of said amplifying means and varying between each power up of said amplifying means, said setting means comprising:
• means for generating a known waveform, said known waveform being operably asserted upon said input of said amplifying means;
• means for comparing a constant signal to said corresponding output of said amplifying means during operable assertion of said known waveform;
• and
• means for changing said set point in response to said comparing means, said set point changing means including:
• means for incrementing said set point by one-half the difference between the current value of said set point and zero when no signal is received from said comparing means;
• means for decrementing by one-half the difference between the current value of said set point and the previous said set point when a signal is received from said comparing means;
• and
• means for storing said current set point as said previous set point.

An amplifier calibration apparatus comprising:

• means for amplifying a signal, said amplifying means having a control, an input and a corresponding output, said control serving to set the gain of said signal between said input and said corresponding output, said amplifying means comprising:
• a first variable resistor, the value of said first variable resistor serving to vary said gain of said signal;
• means for providing a low impedance output, said low impedance output means operably accepting output from said first variable resistor for transmission as said corresponding output;
• means for setting a set point for said amplifying means, said set point corresponding to a zero gain between said input and said corresponding output, said set point being operably asserted upon said control of said amplifying means and varying between each power up of said amplifying means, said setting means comprising:
• means for generating a known waveform, said known waveform being operably asserted upon said input of said amplifying means;
• a second variable resistor serving to set a maximum voltage drop across said first variable resistor in response to the value of said set point to, in turn, limit the full scale gain of said amplifying means;
• means for comparing a constant signal to said corresponding output of said amplifying means during operable assertion of said known waveform, and
• means for changing said set point in response to said comparing means.