VARIABLE GAIN AMPLIFIER WITH TEMPERATURE COMPENSATION FOR USE IN A DISK DRIVE SYSTEM

An apparatus and method for estimating an amplitude of a readback signal obtained from a data storage medium and input to a gain modifying amplifier involves sensing an amplifier output signal in response to a readback signal applied to the amplifier. An amplifier control signal is produced which is representative of a difference between the amplifier output signal and a reference signal. A compensation signal associated with a temperature coefficient of amplifier gain is generated, and an estimate signal indicative of the amplitude of the readback signal is produced using the compensation signal. The estimate signal is representative of readback signal amplitude when the estimate signal has a magnitude equivalent to that of the difference signal and a polarity opposite that of the difference signal. Generating the compensation signal may further involve generating a first compensation signal having a magnitude proportional to absolute temperature and generating a second compensation signal having a magnitude independent of temperature. The first and second compensation signals may be selectively used to cancel temperature related gain and polarity variations in the amplifier control signal. A circuit for estimating an amplitude of a readback signal includes a variable gain amplifier, a temperature compensation circuit, and a comparator, all of which have an equivalent temperature profile and are provided on a common IC substrate. The circuit, which further includes an N-bit DAC and a logic circuit, may be implemented in a disk drive system.