Patent GB-730667-A (GB)
Title: Circuits for generating electric pulse code signals
Inventor: BAGLEY JAMES HAROLD
IPC: H03M1/00
Filed: 1952-10-23
Abstract: 730,667. Pulse code modutation circuits. MINISTER OF SUPPLY. Oct. 23, 1953 [Oct. 23, 1952]. No. 26652/52. Class 40 (5). Relates to sequential coders of the type which determine the code digits in decreasing order of significance and in which repeated comparisions are made of the signal potential to be coded and a single fixed reference potential, the signal being amplified between successive comparisons, such as described in Specification 678,726. According to the invention a gating circuit is interposed between the amplifier and the signal storage device and operated so that during comparison periods the stored signal potential is maintained constant at the peak value to which the amplifier output rises between comparison periods, said output being independent of its rate of rise. In the embodiment described, the storage condenser C, Fig. 3, is periodically charged under the control of pulses S1, Fig. 4 (a), to the potential of the signal to be coded. There is a feed-back path from condenser C through the cathode follower stage CF2, gate circuit diodes D1, D2, amplifier A, charge-sharing capacity C1 and diodes D3, D4. The input of the amplifier is connected to the junction Z of diodes. D1, D2 and through resistance R2, to H.T. +. The amplifier is disabled during. the comparison periods when the gating voltage AG, Fig. 4 (d), applied to the cathode t3 of diode D2, falls to zero. Between these periods the gating voltage rises to H.T. +, diode D1 conducts and junction Z assumes the potential of the storage condenser C. The resultant negative-going amplified output from amplifier A charges the condenser C1, diode D3 clamping the right-hand electrode Y thereof and diode D4 being non-conducting. When the amplifier output returns to zero, the point Y becomes positive, diode D4 conducts and the charges in condensers C, C1 are shared, the dimensions being so arranged that the required amplification of the potential on condenser C results. The output of the cathode follower CF2 is also fed to the slicer S which makes comparisions with the fixed reference potential during the periods when the amplifier A is gated off. These take place when the control wave potential SG, Fig. 4 (c), which is applied to the slicer through transformer T, goes positive. If the comparision results in a code digit pulse being generated at terminal t2, this pulse is also applied to a condenser C2, which is previously charged to the same potential as condenser C, diode D7 which connects them being conducting. When the right-hand electrode of condenser C2 rises in potential, due to the applied code pulse, the charge on the condenser is thereby reduced because the potential of the left-hand electrode is held by diode D6 at its former value. When the pulse ceases this potential falls, diode D6 becomes non-conducting and the charges of C and C2 are shared through diode D7 to reduce the potential of C by the reference potential, the dimensions of the pulse and the condensers being so arranged to produce this result. The amplifier is now gated on and the process repeated five times in the example shown to produce a five-digit pulse code group.