Disk drive with multiplexed read signal and fly-height signal for fly-height monitoring during writing

A magnetic recording disk drive comprising:

• a disk drive base;
• a rotatable magnetic recording disk mounted to the base and having a plurality of data tracks;
• an air-bearing slider maintained near the surface of the disk when the disk is rotating;
• a read/write head on the slider and including a read element for reading from the data tracks and a write element for writing to the data tracks;
• a fly-height sensor on the slider for generating a head-disk spacing signal;
• an electrically-resistive heater on the slider for changing the head-disk spacing;
• a head-positioning actuator for moving the slider and attached head to selected data tracks;
• an arm electronics (AE) module mounted to the actuator and electrically coupled to the read/write head, the fly-height sensor, and the heater, the AE module including a read amplifier for amplifying the signal from the read element and a write driver for sending the write signal to the write element;
• a channel electronics module fixed relative to the base;
• a flex cable connecting the AE module to the channel electronics module and including read path leads for the amplified signal from the read amplifier to the channel electronics module and write path leads for the write signal from the channel electronics module to the write driver;
• and
• wherein the AE module further comprises:
• a variable gain amplifier (VGA) coupled to the fly-height sensor for receipt of the head-disk spacing signal;
• read signal emulation circuitry for generating an oscillatory input signal to the VGA, the VGA generating an oscillatory output signal having an amplitude representative of the head-disk spacing;
• and
• a multiplexer for sending the amplified read signal on the read path leads during reading of data from the data tracks by the read element and for sending the VGA oscillatory output signal on the read path leads during writing of data to the data tracks by the write element;
• and
• wherein the channel electronics module further comprises:
• a read signal detector for detecting the amplified read signal during reading and for detecting the amplitude of the VGA oscillatory output signal during writing, the read signal detector generating an output signal representative of head-disk spacing during writing;
• and
• a fly-height controller coupled between the heater and the read signal detector and responsive to the read signal detector output signal during writing, the fly-height controller generating a control signal to the heater.