Patent GB-1415919-A (GB)
Title: Electronic switching module
IPC: H04Q11/04
Filed: 1973-04-30
Abstract: 1415919 Automatic exchange systems INTERNATIONAL STANDARD ELECTRIC CORP 30 April 1973 [9 May 1972] 20366/73 Heading H4K An integrated circuit crosapoint switching matrix for interconnecting time multiplexed PCM channels comprises for each column of the matrix a control circuit consisting of a receive register RR0 into which the identity of a particular matrix inlet is entered over an address wire ad0, a buffer register RT0 into which the identity is transferred thus permitting entry of a new identity into RR0 and a switching-decoding network DE0 for enabling connection of the specified inlet to the output SO. A plurality of matrices may share the same column in which case a particular matrix, i.e. a particular group of inlets E0-E7 is selected by actuating a matrix gate CVO. The network differs from that in Specification 1,397,840 by its use of a combined decoding/crosspoint array per column, this permitting PCM channels to be switched through in a time considerably less than a time slot so that a plurality of such matrices may be operated in tandem without the need for intermediate buffer stores or staggered timing sequences. The inlets and outlets each comprise 256 channel highways utilizing 500 ns time slots and a 125 Ás repetition rate. The basic switching module, Fig. 1, consists of an eight inlet E0-E7 and eight outlet S0-S7 array of crosspoints PC00-PC77. Each inlet has a store VE0-VE7 which stores the current incoming signalling bit during a phase #6 and continuously emits this bit until the next occurrence of a #6 pulse. Each output has a similar store CV0-CV7 which stores the bit on column lead L0 during a pulse period VAL and then continuously emits it until the next pulse VAL. A crosspoint is addressed by 3 parallel bits in a buffer register TR0-TR7 associated one with each column. The buffers are themselves filled by registers RR0-RR7 which receive the address code in serial format. The basic circuit building block, Fig. 3, comprises two complementary FETs Q7, Q8 which conduct alternatively in dependence on the negative or positive charge on their gate/ substrate capacitance cp3. The charge is derived from the " 0 " or " 1 " logic input at ent when FET Q9 is opened during a phase #i. The circuit inverts a signal passing therethrough. The registers RR0, RT0 (Fig. 4) comprise boxes ET which each contain a complementary pair of FETs as per Q7, Q8 of Fig. 3. In use, a first address bit at ad0 enters ET1 during phase #2 and is passed (phase inverted) to ET2 during phase #4 in which the second address bit is entered into ET4. A second phase #2 follows shortly thereafter to permit the third bit to enter ET1. At a phase #6 the first, second and third bits are passed (non-inverted, inverted and inverted respectively) to boxes ET70, not shown, and ET51 in buffer RT0. The address bits in inverted and non-inverted form are thereby made available in parallel at terminals sd0-sd2 until the next phase #6. Crosspoint operation, Fig. 5.-Assuming the requirement is to connect input I0 with output L0, the necessary address code sd0, sd1, sd2 is 1, 1, 1 which means that FETs, Q51, Q53 and Q55 are gated open. The digit signal on I0 is thereby permitted to charge cpl. After a sufficient charging time Q5 is gated off to isolate the output store from the crosspoint network and Q1 and Q4 are gated on so as to permit one of Q2, Q3 to apply a 1 or 0 condition to outlet S0. It may be noted that the two FETs in the pairs Q55, Q56; Q53, Q54; Q51, Q52 &c. are complementary. Crosspoint operation. Fig. 7.-Here input I0 reaches output. L0 during a gating period defined by an enabling pulse STA which is a little longer than the propagation time of a digital pulse through the gates Q51-Q55. Just prior to the end of STA, enabling pulse VAR is applied so as to permit entry of the digital data into the gate/substrate capacitance of FETs Q12, Q13. If the input signal is a " 0 " it passes via Q19 to open Q12 and via Q21 to maintain Q13 closed. If the signal is a " 1 " it passes via Q20 to maintain Q12 closed and via Q22 to open Q13. The original data at inlet E0 is thus passed uninverted to outlet S0. After a short period, pulse VAR is reapplied to close Q19, Q20, Q21, Q22 and to open Q11 and Q14. The latter close Q12 and Q13 whereby the output digit on S0 is removed. The entry of the subsequent crosspoint address into buffer RT0 during phase #6 coincides with the restoration of enabling pulse STA. Enlarged matrix.-A 16 x 8 array is provided by paralleling the inlets or outlets of two 8 x 8 arrays. Discrimination is effected (assuming the same 3 digit address scheme is adopted for both 8 x 8 arays) by maintaining the VAL pulse (Fig. 1) on that array whose inlets are not to reach the outlet, e.g. S0.