Patent GB-1409910-A (GB)
Title: Semiconductor data stores
IPC: H03K3/356
Filed: 1972-09-27
Abstract: 1409910 Data store SIEMENS AG 27 Sept 1972 [30 Sept 1971] 44645/72 Heading G4C [Also in Division H3] A data store comprises a plurality of onetransistor storage cells each comprising a capacitor and a transistor whose control input is connected to a selector device, and an evaluator and regenerator circuit 31 connected to the cells by a digit line and comprising a flip-flop having a controlled semi-conductor switch connected between its two outputs. As described two sets of storage cells, each comprising an FET and a capacitor (e.g. 41, 42, 51, 52) are connected via respective digit lines 40 and 50 to an evaluating and regenerating circuit 31. Several digit line pairs and associated circuits 31 may be provided, selection of one or a group of digit lines being by means of a decoder 43 receiving address inputs 80. Word decoders 44 and 55 are also provided in order to select a word line in response to address signals 60 so that a single storage cell may be selected. The word decoders contain a circuit 144, 154 which enables transistors 145, 155 to connect a capacitor 245, 255 to the circuit 31, each capacitor transistor pair 145, 245 and 155, 255 being identical to a storage cell. Capacitors 13 and 15 represent the capacitance of the digit lines 40 and 50. Two embodiments of circuit 31 are described. In each embodiment switching transistors 2 and 4 with respective load transistors 6, 8 are connected as a flip-flop having outputs 3 and 5. In the first embodiment a transistor 10 is connected between the outputs, its gate being connected to a control input 11 (32 in Fig. 3). In the second embodiment, Fig. 2 (not shown) points 3 and 5 are interconnected via two series transistors (20), (21) whose gates and drains are connected to the control input (32 in Fig. 3). Inputs 7 and 9 are power supply inputs. In operation points 3 and 5 are brought to the same potential by switching transistor 10 conductive. Assuming cell 41 is to be read, logic circuit 144 switches transistor 145 conductive to charge capacitor 245 to the potential on points 3 and 5. Transistor 145 is then switched non-conductive and simultaneously or after a delay the potentials applied to points 7 and 9 are switched such that flip-flop 2, 4 consumes no power. Transistor 10 is then switched non- conductive and a cell is selected for read out by switching its transistor, e.g. 141, conductive. The charge stored on capacitor 142 is thus distributed between capacitor 142 and the capacitance 15 of the digit line. Thus in accordance with the charge on capacitance 142 capacitance 15 undergoes a net charge or discharge due to the signal from the selected cell and also due to unavoidable interference signals. In order to compensate for the latter transistor 145 is switched conductive simultaneously with cell selection and a charge compensation occurs between capacitance 245, which is identical to the selected cell capacitance, and the capacitance 13 of digit line 50. In this way the potential difference applied across points 3 and 5 is determined only by the true read out signal from the selected cell. The potentials at inputs 7 and 9 are then restored and flip-flop 2, 4 is triggered into one of its stable states in accordance with the potential difference between points 3 and 5. The flip-flop acts to regenerate any charge previously stored on the capacitance 142 of the selected cell via the still conductive cell transistor 141. Transistors 141 and 145 are then switched non-conductive and read out of the state of flip-flop 2, 4 is made via digit line 40 and output 443 on bit decoder 43. Read out from a cell in bank 500 is performed in an exactly similar manner, capacitor 255 serving to compensate for interference signals. To store a datum in a cell a signal on input 444 is switched to the selected digit line. By using the second embodiment of circuit 31 points 3 and 5 may initially be brought to a selected reference potential applied to control input 32. In this way a desired threshold can be set for the read out signal, below which flip-flop 2, 4 does not respond. The store may be fabricated on an integrated circuit.