Controlled impedance amplifiers

Abstract

A hard disk drive (HDD) circuit (10) having feedback provided to an input of an differential amplifier setting the amplifier input impedance close to a flexible printed circuit (FPC) characteristic impedance. A matched source and input impedance produces a generally flat gain frequency response. As the result of flat response and wider gain bandwidth, white noise without high frequency peaking can be obtained. Feedback resistors (R5) provide feedback according to the present invention which is superior in terms of the input referred noise since the feedback attenuates both the input signal from the sensor and the noise from the amplifier. Feedback resistors (R5) may be connected through AC coupling capacitors to compensate the voltage differences between amplifier input and output. The circuit of the present invention provides a method to connect the feedback resistors directly from amplifier outputs to inputs which have a different potential. The advantages of the present invention include matched impedance results and a better system level frequency response, the direct feedback connection eliminates costly on-chip capacitors, and the input impedance can be adjusted by the amount of feedback.

Dependencies are inferred from the claim text.