Patent GB-1159822-A (GB)
Title: Gated Storage Elements for a Semiconductor Memory.
IPC: G11C19/28
Filed: 1966-07-29
Abstract: 1,159,822. Shift registers. MOTOROLA Inc. 29 July, 1966 [9 Sept., 1965], No. 34115/66. Heading G4C. [Also in Division H3] A cross-coupled transistor-type bi-stable circuit suitable for use in a shift register is set to a desired state by diverting its current to alternative paths which determine the state of the bi-stable circuit when the current is restored. In Fig. 3, block 100 comprises four transistors 111, 112, 105, 106 crosscoupled to form a bi-stable circuit supplied with current through a normally conducting transistor 116 of a current switch 114, 116. To reset the circuit a clock pulse is applied through an emitter follower 118 to cut off 116 and divert the current through transistor 114 towards setting transistors 107, 110. An input signal is applied to the base of 110 and this is compared with a temperature stabilized bias voltage applied from 99 block to the base of 107 so that the current flows to one or other of the setting transistors depending upon whether the signal at 172 is " up " or " down." This current generates a voltage across load resistors 120 or 122 of the bi-stable circuit which so polarizes a circuit that when the clock pulse terminates and the current switch accordingly restores current to the bi-stable circuit the latter will set itself to the corresponding state. Block 102 shows a similar circuit but which differs mainly in that the function of the current switch transistors 149 and 150 is interchanged with respect to the corresponding transistors in block 100 so that the circuit works in the opposite phase of the clock pulse. Moreover, the input to transistor 144 is derived from the output of block 100 instead of the stabilized source 99. Alternative set and reset arrangements are provided by transistors 164 and 166. Fig. 3 may operate as one stage of a shift register with an input at 172 and an output from 153 to the next stage. The register may have parallel input transfer. Alternatively the circuit may be arranged to act as a toggle by connecting output terminal 130 of block 102 to the input base of transistor 110 of block 100. Fig. 1 (not shown) operates in a manner similar to the two blocks of Fig. 3 and further includes an output AND gate (65) for reading out the state of the circuit. In Fig. 2 the basic bi-stable circuit is of the Schmitt type and comprises transistors 18 and 10 coupled by an emitter follower 30 and by a common emitter resistor 49. To set the state of the circuit a clock pulse applied to the base of transistor 44 of a current-switch 44, 60, interrupts a current through the bi-stable circuit and diverts it through transistor 60 towards setting transistors 50 and 55. These transistors compare the input signal with a bias voltage VBB1 applied to the base of 55 and current is either passed through resistor 36 or not depending upon whether the input signal is " up " or " down." The input circuit of Schmitt circuit transistor 30 is so conditioned that when current is restored to the Schmitt circuit at the end of the clock pulse the latter circuit will take up a corresponding state. In the above circuits the current level is such that the transistors of the bi-stable circuit do no saturate.