Patent GB-1336482-A (GB)
Title: Stored charge memory apparatus
IPC: G11C11/4067
Filed: 1971-11-17
Abstract: 1336482 Semi-conductor storage cell INTERNATIONAL BUSINESS MACHINES CORP 17 Nov 1971 [27 Nov 1970] 53413/71 Heading H3T [Also in Division G4] A data store comprises an array of semiconductor cells each comprising a bipolar transistor and each adapted to capacitatively store a binary digit in a non-bi-stable mode, the store further including addressing means to periodically replenish the charge in cells storing a charge. Storage cells.-Several suitable memory cells are described none of which are latchable in the manner of a bi-stable. The cell illustrated in Fig. 1 comprises a PNP and an NPN transistor connected as shown. To read data stored in the cell the potential on line X1 is raised to a positive level causing T1 to conduct if Cj is charged with A more positive than B; Cj is thus discharged and a voltage pulse appears on line Yo. If Cj is charged so that A is more negative than B, T1 does not conduct and no pulse appears on Yo. To write data into the cell X1 is raised to a positive level and current is fed via line Xo. To write binary 0 the corresponding Yo line is left at zero potential so that T1 conducts the current from line Xo causing A to go negative with respect to B. To write binary 1 Yo is raised to a positive level biasing T1 off and causing A to go positive with respect to B. Regeneration is performed periodically by reading and re-writing data in the cells. In an alternative mode of operation "0" is first written into the cells as above. To write "1" into the cell word line X1 is biased negative while current is supplied to emitter T2. For operation in this mode word line Xo is extended parallel to bit line Yo. Another suitable cell is illustrated in Fig. 5, the data being stored on the parasitic capacitance 62. A write 0 operation is performed by raising line 24 and the select line 28 to + 3 volts. Transistor 50 is reversed biased and non-conductive and no charge is stored at 62 To write. binary 1 line 24 is raised to + 3 volts and line 28 is lowered to about 2À3 volts so that transistor 50 conducts and capacitance 62 charges to a positive level of about 2À8 volts. During writing transistor 54 remains non-conductive so that no D.C. path exists between lines 24 and 26. To read data from the cell line 26 is lowered to zero volts so that if a binary 1 is stored the charge in capacitance 62 renders transistor 54 conductive and the charge is dissipated in a destructive read operation. Conversely if binary 0 is stored transistor 54 remains non-conductive. Other suitable cells are described with reference to Figs. 6-10 (not shown). The cells may be formed on a monolithic integrated circuit. Matrix organization.-In order to select a cell in an array of cells, Fig. 4, X and Y decoders, 10 and 12, are provided. Each column of cells has an associated regenerating and switchable current source illustrated in Fig. 12. During read operations a single AND gate 38 is enabled to select a column. The regenerating and switchable current source shown in Fig. 12 is adapted for use with the cells of Fig. 5 arranged in the array of Fig. 4. A pair of transistors 151 and 152 are differentially connected between +3 and 0 volt voltage source and a reference transistor 154 is connected to transistor 152 and output line 36. The output line 36 is connected to a clamping arrangement comprising diode 156 and resistor 158. During a destructive read 0 and rewrite 0 operation line 32 is raised to + 3À8 volts, transistor 151 conducts and transistors 152 and 154 do not conduct. Line 36 is at +3 volts so that the common sense line 28 of the array is also at 3 volts. Similarly during a write or rewrite 1 operation line 32 is lowered below 3À8 volts and line 34 below 1À5 volts so that both transistors 151 and 152b are non-conductive and transistor 154 is conductive. Current flows through load resistor 160 and an output pulse of about 2À3 volts appears at output 36 and hence on the common select line 28 of the array. In practice the sense lines 28 are formed by diffused lines in an integrated circuit clip and thus exhibit a parasitic capacitance. Large voltage excursions would thus normally result in an unnecessary power loss. To avoid this the regenerating circuits 30 are clamped to a selected cell so as to limit the voltage excursions.