Patent GB-1473028-A (GB)
Title: High density logic array
IPC: H03K19/177
Filed: 1975-09-16
Abstract: 1473028 Logic INTERNATIONAL BUSINESS MACHINES CORP 16 Sept 1975 [30 Dec 1974] 37917/75 Heading G4H [Also in Division H1] A logic chip comprises at least two arrays 10, 14 and a string of latches 30 in which one of the arrays 10 receives signals from decoders 16 and feeds the responses thereto to the second array 14 which in turn supplies inputs to the latches 30, wherein the input lines 18 to the decoders and the output lines 67 from the latches extend in a side by side relationship; and a series of rails 62 cross the input and output lines, individual rails being electrically coupled to certain of the input and output lines and electrically isolated from others and having breaks therein which divide the rails into segments so that signals on different segments of the same rail are electrically isolated from one another. As disclosed, each decoder decodes 2 bits to 1-outof-4 form, array 10 performing AND functions of decoder outputs, a typical AND function being the AND of one or more outputs of the same decoder (one output of which carries 0 and the rest 1) so a required Boolean combination of the two inputs of the decoder can be formed by suitable couplings (shown as dots) on a column of array 10. The rows of array 10 are broken at notional line 36 so the right and left parts of the array are used by the respective decoders, but connections such as 34 in a terminal box 31 permit functions in the two parts to be ANDed together. The second array 14 performs OR functions on the outputs of the array 10 in one part thereof (the columns being broken at notional line 38) and on the outputs of another AND array 12 (similar to the first) in another part, array 14 feeding the latches 30 which are connected in series to form a shift register. Input pads 74a along the top and bottom of the chip feed the decoders 16 via the rails 62. Input and output pads 74b along the sides of the chip are connected to the rails 62, the ends of the series of latches 30, and off-chip drivers (amplifiers) 66 connected to the rails 62. Since the latches can feed the decoders via the rails, sequential logic can be performed. Integrated circuitry construction details.-In array 10, the coupling between rows and columns are FET's. Each column is a diffusion stripe in oxide, an earthed diffusion stripe being provided per two columns. These stripes and the oxide in which they exist are covered with an oxide layer over which the rows are formed as metal stripes with protrusions down into the oxide layer to form the gates of the FET's where FET's are required, part of a column diffusion stripe and of an earthed diffusion stripe forming the source and sink. A typical metal row stripe has a gap at a point along its length to break the row as stated. Array 12 is similar. Array 14 differs in that the diffusions run horizontally and the metal stripes run vertically, the metal stripes being connected to the diffusions of arrays 10, 12 by means of conductive vias through the oxide layer. An alternative construction for each array has a FET at each row/ column intersection, the gate being connected to the row or the earthed diffusion according as the FET is required or not. The rails 62 consist of conductive diffusions in the substrate covered by an oxide layer and joined by metallized via holes through the oxide to metal portions on top of the oxide, the metal portions also forming parts of the rails, i.e. each rail consists of diffusions and metal portions alternatively but with breaks as stated to divide the rails into mutually isolated segments. Connections to the metal portions of some rails pass over the location of the diffusions of other rails, so that these connections (metal) are provided in the same operation as the rail metal portions. Bipolar technology is mentioned as an alternative to FET.