Low amplitude skip write detector

A disc drive comprising:

• a disc for magnetically storing data in one or more data sectors situated between consecutive servo sectors;
• a read head for reading data from the disc;
• a variable gain amplifier operably coupled to the read head for receiving a signal from the read head, the gain of the variable gain amplifier being controlled by a control signal;
• a gain controller operably coupled to the variable gain amplifier for generating the control signal;
• a microprocessor operably coupled to the gain controller, the microprocessor having access to a digital representation of the control signal, the microprocessor being programmed to
• characterize the control signal during at least two instances during which the read head passes over a servo sector;
• execute a write event;
• acquire the control signal as the read head passes over the following servo sector, after the write event;
• and
• compare the acquired control signal to the characterization of the control signal in order to detect a write irregularity.

A method of determining a fly height of a head within a disc drive, comprising:

• obtaining a characterization of a first read-back control signal over a duration of time;
• obtaining a second read-back control signal;
• and
• comparing the second read-back control signal with the characterization, thereby obtaining data revealing information regarding the fly height of the head.