EP0034055A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Variable window data recovery apparatus and method
Assignee: Unisys Corp
•
Filing: 1981-02-06
•
Granted: —
•
Expires: 2001-02-06
Abstract
Abstract In a data recovery system, encoded variable bit-spaced digital data are recovered by providing variable width windows which are widened or narrowed to tend to centre on the expected occurrence of data signals as a function of the contents of the current or the immediately preceding timing units and of characteristics of the encoding scheme. The system employs pulse by pulse synchronization without modifying the underlying overall synchronization. The first occurrence of a shifted, e.g. delayed, signal serves as reference point for the window size for subsequent signals. The window for a reference pulse is expanded at its trailing edge if, for example, the reference pulse is delayed beyond the normal tolerance of the detection system. The leading edge of a window for the subsequent signal is initially advanced, and, if no signal occurs within that window, its trailing edge is advanced too. A circuit (10) employs a Read Only Memory (18) and recycling window (20) and signal position (16) counters to modify recovery windows according to the invention. The encoding technique is particularly applicable to data storage and retrieval systems employing encoding schemes such as Modified Frequency Modulation (MFM) coding and the like.
Inventors
- 👤 Anthony Kwok Fung
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-29 21:51
CPC Classifications
G; G11; G11B; G11B20/00; G11B20/10; G11B20/14; G11B20/1403; G11B20/1423; G11B20/1407; G11B20/1419
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
104 words
A method of recovering data from a serial signal stream divided into a sequence of bit cells each having two distinct locations at which a signal may occur, wherein respective recovery windows are used to distinguish between signals which occur at the first, and signals which occur at the second of these locations, characterised in that the recovery windows are synchronized with the nominal bit cell rate and are capable of being varied by expansion and contraction to permit detection of signals at shifted positions which are predicted from measuring the position of a shifted signal present at a previous location as reference signal.
Claim 2
Independent Claim
104 words
A method of recovering data from a serial signal stream divided into a sequence of bit cells each having two distinct locations at which a signal may occur, wherein respective recovery windows are used to distinguish between signals which occur at the first, and signals which occur at the second of these locations, characterised in that the recovery windows are synchronized with the nominal bit cell rate and are capable of being varied by expansion and contraction to permit detection of signals at shifted positions which are predicted from measuring the position of a shifted signal present at a previous location as reference signal.
Claim 3
Dependent Claim
50 words
A data recovery method as claimed in claim 1 wherein the recovery windows form a sequence of complementary signal levels of equal duration centred respectively about the centre of the first and second locations, and are expanded and contracted by appropriate shifting of the boundary transitions between adjacent recovery windows.
Claim 4
Dependent Claim
60 words
A data recovery method as claimed in claim 1 or 2 in which the reference signal is a delayed signal whose detection is arranged to delay the termination of the current recovery window, and to cause expansion of the next but one recovery window of the opposite type by advancing the start thereof through corresponding contraction of the intervening windows.
Claim 5
Dependent Claim
141 words
A data recovery method as claimed in claim 3 to recover data encoded as a signal stream in which signals may occur either at the centre of the bit cells or at the boundaries between adjacent bit cells, wherein the first and the second recovery windows are centred about the centres and the boundaries respectively, and wherein, if a delayed signal is detected in said next but one recovery window of the opposite type its trailing edge is delayed and it becomes a new reference signal, and the appropriate next but one following window is expanded by advancing its leading edge, and wherein, if a signal is not detected within said next but one recovery window of the opposite type, the subsequent adjoining recovery window of the same kind as the original recoverry window is expanded by advancing its leading edge.
Claim 6
Dependent Claim
32 words
A method as claimed in claim 4, in which the first and second recovery windows are each arranged to last half a bit cell to recover data encoded in modified frequency modulation.
Claim 7
Dependent Claim
171 words
Data recovery apparatus including a recovery window generator (10), to recover data from a serial signal stream in which signals may occur at distinguishable first or second locations of a bit cell, characterised in that the recovery window generator (10) is synchronized to the bit cell rate and comprises a recirculating recovery window counter (20), a recirculating signal position counter (16), arithmetic means (18) whose outputs preload the signal position counter (16) in response to a combination of inputs received from the recovery window counter (20), from the signal position counter (16), and from a latching circuit (22) which receives as input selected outputs from the arithmetic means (18) and which operates to cause the arithmetic means (18) to modify the preload to the signal position counter (16) in accordance with previous outputs from the arithmetic means (18) and the signal position counter (16), and a window latching circuit (14) acutated on completion of counting cycles of the signal position counter (16) thereby to define the boundaries of the recovery windows.
Claim 8
Dependent Claim
171 words
Data recovery apparatus including a recovery window generator (10), to recover data from a serial signal stream in which signals may occur at distinguishable first or second locations of a bit cell, characterised in that the recovery window generator (10) is synchronized to the bit cell rate and comprises a recirculating recovery window counter (20), a recirculating signal position counter (16), arithmetic means (18) whose outputs preload the signal position counter (16) in response to a combination of inputs received from the recovery window counter (20), from the signal position counter (16), and from a latching circuit (22) which receives as input selected outputs from the arithmetic means (18) and which operates to cause the arithmetic means (18) to modify the preload to the signal position counter (16) in accordance with previous outputs from the arithmetic means (18) and the signal position counter (16), and a window latching circuit (14) acutated on completion of counting cycles of the signal position counter (16) thereby to define the boundaries of the recovery windows.
Claim 9
Dependent Claim
53 words
Apparatus as claimed in claim 6, wherein the arithmetic means (18) comprises a memory addressed by combinations of output signals from the window counter (20), the signal position counter (16) and the latching circuit (22), with the signal position counter (16) being preloaded with the bit value stored at the address so selected.
Claim 10
Dependent Claim
67 words
Apparatus as claimed in claim 6 or claim 7, wherein the arithmetic means is a Read Only Memory (18) arranged to store selected address values such that an input address comprising a value equal to the delay in the completion of a counting cycle immediately following initialization, addresses a. memory location whose contents operate to shorten the counting cyle for a subsequent window of the same type.
Claim 11
Dependent Claim
46 words
Apparatus as claimed in claim 8 wherein the input of selected further addresses to the Read Only Memory (18) provides output values which operate to expand a selected recovery window, occurring after a predetermined sequence of recovery windows subsequent to initialization, by advancing its leading boundary.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.