Patent GB-1327926-A (GB)
Title: Electrical delay circuits
IPC: G11B20/20
Filed: 1971-05-28
Abstract: 1327926 Pulse delay circuits INTERNATIONAL BUSINESS MACHINES CORP 28 May 1971 [20 July 1970] 17815/71 Heading H3T [Also in Division G5] An electrical delay circuit comprises a first circuit 11, Fig. 2, for providing first signals in response to transitions between one and other level in a received data signal C, amonostable device 15 with a selectively variable unstable state time responsive to the first signals to provide a signal of duration determined by the unstable state time of the device for each transition between one and another signal level in the received digital data signal C, a bi-stable device 18 which switches between its stable states in response to the end of each signal from the monostable device 15 and a feedback path from the output of the bi-stable device 18 to the first circuit 11 through which an output signal from the bi-stable device conditions the operation of the first circuit 11 whereby the output signal has the same time gap between transitions as the received digital data signal delayed by the unstable state time. For writing NRZ data at C,) Fig. 4 not shown), inputs B and M apply signals to enable NAND gates A1, A2 and inhibit NAND gate A7. A reset signal at A conditions latch NAND gates A5, A6 so that feedback via 70, 71 enables A2 and inhibits A1. A complementary signal from inverter I at D to gate A2 produces a negative going output at F which causes monostable 15 to produce a positive going pulse at G. The negative going transition of the output pulse from the monostable 15 is sensed by differentiator 81 to produce a positive going output at H. This is fed to a NAND gate A3, which is enabled by the signal at D, to change the state of the bi-stable formed by NAND gates A5, A6 and produce a negative going output at L. The output at K enables NAND gate A1 and the positive going NRZ1 data input at C produces a negative going signal at E which causes the monostable 15 and diffe. rentiator 81 to produce a positive going pulse at H. NAND gate A4 is enabled by the input on 88 so as to generate a negative going output pulse at J which causes a positive going output pulse at L. When a phase encoded (PE) data input is applied to the input C the input to B inhibits NAND gates A1, A2 and an input to M enables NAND gate A7 so that the complement of data on C passes via NAND gate A7 and causes an output at L (Fig. 5, not shown). The monostable device 15 may be a transistor 100 (Fig. 3) which is conductive in its stable state and is turned off by a negative input at E or F for a time determined by the time constant of 102, 103. The differentiator 81 may consist of a capacitor 104 and a resistor 105, the output being from a transistor 106 which becomes conductive for a short period in response to a negative going output at G. In a nine track recording system (Fig. 6, not shown) the data tracks (30-38) feed respective delay circuits (39-47) as described above which have delay times selected so as to compensate for the gap scatter pattern at wire heads (48- 56) associated with a single magnetic head so as to produce position coincidence recording on a tape (57).