High speed gain stage with DC offset cancellation for servo demodulator circuit

A gain stage for converting servo burst signals, including:

• a transconductance amplifier which is configured to receive differential voltage signals that represent servo bursts, the transconductance amplifier converting the differential voltage signals into corresponding differential current signals;
• a full-wave current rectifier connected to the transconductance amplifier such that the full-wave current rectifier receives the differential current signals from the transconductance amplifier and the full-wave current rectifier outputs a rectified current signal, the full-wave current rectifier having a first forward conduction path configured to allow current flow in only a single direction defining a full-wave rectified current output having a first polarity, the full-wave current rectifier further having first and second reverse conduction paths, each path constructed as a mirror image of the other and each path configured to allow current flow in a single direction opposite the direction of the forward conduction path, each path connected to a respective one of the differential current signals of the transconductance amplifier at a first end and combined together at a second end to define a full-wave rectified current output having a polarity opposite the first polarity;
• a transimpedance amplifier connected to the full-wave current rectifier such that the transimpedance amplifier receives the rectified current signal from the full-wave rectifier and the transimpedance amplifier converts the rectified current signal into a rectified voltage signal, each of the full-wave current rectifier and the transimpedance amplifier having symmetrical mirror image signal paths;
• an integrator circuit which is configured to receive the rectified voltage signal from the transimpedance amplifier and integrate the received rectified voltage signal such that a signal representing magnitude of a servo burst is generated;
• and
• signal storage means connected to the integrator circuit for temporarily storing the signal representing the magnitude of the servo burst.

A servo system demodulator for converting servo burst signals representing read/write transducer head position information into digital signals, the demodulator comprising:

• a gain stage, including:
• a transconductance amplifier which is configured to receive differential voltage signals representing servo bursts, wherein the transconductance amplifier converts the differential voltage signals into corresponding differential current signals;
• a full-wave current rectifier connected to the transconductance amplifier to receive the differential current signals from the transconductance amplifier, the full-wave current rectifier having a forward conduction path and a reverse conduction path which is symmetrical to the forward conduction path, where the forward conduction path allows current flow in a first direction and the reverse conduction path allows current flow in a second direction opposite the first direction, wherein the forward conduction path rectifies the differential current signals and the forward conduction path of the full-wave current rectifier outputs a corresponding rectified current signal having a first polarity, and wherein the reverse conduction path comprises a first reverse conduction path and a second reverse conduction path which is a mirror image of the first reverse conduction path, the first reverse conduction path and the second reverse conduction path being individually connected to the differential current signals at a first end, and wherein the first reverse conduction path and the second reverse conduction path are combined together at a second end to define a reverse full-wave rectified current output having a second polarity that is opposite the first polarity of the forward full-wave rectified current signal;
• and
• a transimpedance amplifier which is connected to the full-wave rectifier, wherein the transimpedance amplifier receives the rectified current signal and converts the rectified current signal into a rectified voltage signal.