# US 5,708,537 A · Intelligent envelope detector and method for gain control for PRML data and servo channels including polarity detection > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,708,537 A - Document ID: US5708537A - Status: Granted - Kind: A - Application number: 08/555,781 - Filed: 1995-11-09 - Granted: 1998-01-13 - Earliest claimed: 1995-11-09 - Assignees: International Business Machines Corporation - Inventors: Richard Leo Galbraith; David James Stanek - Web page: https://patentgrep.com/patent/US5708537A ## CPC - G11B 20/10055: {using partial response filtering when writing the signal to the medium or reading it therefrom} - G11B 5/09: Digital recording - G11B 20/10009: {Improvement or modification of read or write signals} - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract A method and apparatus are provided for gain adjustment of a signal. A plurality of comparators compare the signal with a plurality of threshold values. An envelope detector coupled to the comparator includes a peak capture function for detecting the amplitude of the signal and a polarity memory for detecting polarity of the signal. A gain control function for setting a gain correction value is responsive to the peak capture function and the polarity memory. Features of the signal gain adjustment method and apparatus of the invention include an intelligent hold of the gain control over both thermal asperities and null gaps in the signal. ## Claims ### Claim 1 Apparatus for gain adjustment of a signal comprising: comparator means for comparing the signal with a plurality of threshold values and providing a compared signal; capture means coupled to said comparator means for detecting amplitude of the compared signal; polarity memory means coupled to said comparator means for detecting polarity of the compared signal; gain control means for setting a gain correction value responsive to said capture means and said polarity memory means; and timer means coupled to said comparator means for identifying a selected time period for the signal being below a predetermined threshold value and holding the set gain correction value having said identified selected time period. ### Claim 2 (depends on 1) Apparatus for gain adjustment of a signal as recited in claim 1 wherein said gain control means sets a predetermined gain correction value responsive to said timer means. ### Claim 3 (depends on 1) Apparatus for gain adjustment of a signal as recited in claim 1 wherein said timer means is a programmable timer. ### Claim 4 (depends on 3) Apparatus for gain adjustment of a signal as recited in claim 3 further includes multiplexer means coupled to said timer means for selecting a servo timer value or a data timer value. ### Claim 5 (depends on 1) Apparatus for gain adjustment of a signal as recited in claim 1 wherein said gain control means for setting a gain correction value is held for the signal being a single polarity. ### Claim 6 (depends on 1) Apparatus for gain adjustment of a signal as recited in claim 1 wherein said comparator means include means for receiving the analog input signal and for generating a plurality of digital output signals responsive to comparing the signal with said plurality of threshold values. ### Claim 7 (depends on 1) Apparatus for gain adjustment of a signal as recited in claim 1 wherein the signal is a readback signal in a direct access storage device and wherein said gain control means for setting said gain correction value responsive to said capture means and said polarity memory means is used for both data and servo signals. ### Claim 8 (depends on 7) Apparatus for gain adjustment of a signal as recited in claim 7 wherein said gain control means is held for a thermal asperity in the signal. ### Claim 9 (depends on 1) Apparatus for gain adjustment of a signal as recited in claim 1 wherein the signal is a readback signal in a direct access storage device and wherein timer means includes said predetermined time interval being selectively provided for a data signal and a servo signal. ### Claim 10 A method for gain adjustment of a signal comprising the steps of: comparing the signal with a plurality of threshold values and providing a compared signal; detecting amplitude of the compared signal; detecting polarity of the compared signal; setting a gain correction value responsive to the detected amplitude and the detected polarity of the compared signal; and identifying a selected time period for the signal being below a predetermined threshold value and holding the set gain correction value during said identified selected time period. ### Claim 11 (depends on 10) A method for gain adjustment of a signal as recited in claim 10 wherein the step of comparing the signal with a plurality of threshold values and providing a compared signal includes the step of receiving art analog input signal; comparing the analog input signal with said plurality of threshold values and generating a plurality of digital output signals responsive to the compared values. ### Claim 12 (depends on 10) A method for gain adjustment of a signal as recited in claim 10 wherein the step of setting said gain correction value responsive to the detected amplitude and the detected polarity of the signal includes the step of holding a gain correction value responsive to no change in the detected polarity. ### Claim 13 A method for gain adjustment of a readback signal for partial-response maximum-likelihood (PRML) and servo channels in a direct access storage device (DASD) comprising the steps of: comparing the readback signal with a plurality of threshold values and providing a compared signal; detecting amplitude of the compared signal; detecting polarity of the compared signal; setting a gain correction value responsive to the detected compared signal amplitude and a detected change in polarity of the compared signal; and identifying a selected time period for the readback signal being below a predetermined threshold value and holding the set gain correction value during said identified selected time period. ### Claim 14 (depends on 13) A method for gain adjustment of a readback signal for partial-response maximum-likelihood (PRML) and servo channels as recited in claim 13 further includes the steps of identifying a selected time period for the readback signal being below a predetermined threshold value and holding a gain correction value during said identified selected time period and wherein said selected time period includes a first (PRML) data programmable value and a second servo programmable value.