Patent GB-843951-A (GB)
Title: Improvements in memory systems
IPC: G11C11/22
Filed: 1956-12-21
Abstract: 843,951. Circuits employing bi-stable dielectric elements. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 21, 1956 [Dec. 27, 1955], No. 39120/56. Class 40 (9). [Also in Group XIX] A ferro-electric storage matrix 10, Fig. 1, is driven by half-select pulses from biased ferroelectric switching matrices 25R, 25C which are separately controlled by address pulses commencing at the same time and of different durations, the application of an address pulse to a switching matrix reversing the polarization state of a selected capacitor for the duration of the pulse and producing a half-select reading pulse which acts in combination with a similar pulse of opposite polarity from the other switching matrix to drive a single capacitor in the storage matrix to a remanent polarization state representing binary zero, while termination of the address pulses permit the selected switching capacitors to be restored by the bias to their original saturation state and so produce writing pulses of the reverse polarity which are normally in different time positions and are therefore unable to set the selected storage capacitor in the binary one remanent state. The address pulse applied to the column switch matrix 25C is normally of the longer duration, and to write a binary one in the store the row and column switch matrices are restored simultaneously by opening a column gate 32C in the column address pulse circuit. General arrangement. The storage matrix 10 comprises a single barium titanate crystal with row and column electrodes forming individual capacitors at their crossing points. Read-out is detected by a transformer the core 12 of which is coupled with all the matrix column leads, and spurious outputs due to halfselect pulses applied to unselected capacitors are suppressed by the wiring arrangement which includes separating the column electrodes of the storage matrix into upper and lower halfs. The secondary winding 14 of the transformer is connected to a read-out signal amplifier 16 over a rectifier network 85 which includes a transformer 93, the latter component introducing a zero cancel voltage which completely neutralizes the small output arising when an interrogated capacitor already in the binary zero remanent state is driven to saturation. Address circuits. An address pulse source 34 applies negative pulses over a lead 33R and a lead 34R to a row gate 32R, and positive pulses over a lead 33C and a lead 34C to a column gate 32C, each pulse having an initial duration t1-t3 in a cyclic time period t1-t4. The row gate is controlled by clock pulses on lead 35 so that the row address pulses are shortened to t1-t2. The row and column pulses are respectively applied through row and column transistor inverter-amplifiers 30R, 30C to the switch matrices. These pulses cause a selected capacitor in each biased switch matrix to change its polarization state and produce a half-select reading pulse in period t1-t2. The two halfselect pulses thus produced are of opposite polarity and together drive a single storage matrix capacitor to the binary zero remanent state. If the interrogated capacitor is initially registering a binary one, polarization reversal takes place and current in a column lead 10C induces an output in the secondary winding 14 of the transformer which is amplified at 16. When the address pulses terminate, the selected capacitor in each switch matrix reverts by bias action to its original polarization state and produces a half-select writing pulse of reverse polarity. As the row and column address pulses to the switch matrices terminate at the ends of periods t 1 -t 2  and t 1 -t 3  respectively, the halfselect writing pulses which arise in the time periods t 2 -t 3  and t 3 -t 4  are non-coincident and have no effect on the storage capacitors in matrix 10. Although these writing pulses are each insufficient to switch a capacitor they tend to neutralize the gradual destruction of remanent polarization by half-select pulses applied to capacitors not chosen for interrogation. Rewriting information read out from the storage matrix. This is carried out by bringing the two switching matrices back to their initial state at the end of period t 1 -t 2  so that the halfselect writing pulses become coincident in period t 2 -t 3 . If a binary one remanent state is detected in an interrogated storage capacitor, the signal amplifier 16 produces a delayed output in period t 1 -t 2  which acts with a re-write pulse on lead 42 through an AND gate 22 and an OR gate 36 to open column gate 32C. This reduces the address pulse to the column switch matrix to the same duration t 1 -t 2  as that applied to the row switch. If the information stored was binary zero, then amplifier 16 is inoperative and the column gate remains open so that a binary zero state continues to be registered. Writing new information. In the absence of a pulse on lead 42, binary zero is written into the storage matrix. If a binary one is to be introduced as new information, a pulse is applied to lead 44 which acts through OR gate 36 to open column gate 32C at the end of period t 1 -t 2 . Inverter circuits. The row inverter, Fig. 2, includes a P.N.P. junction transistor in each row lead 29R, 31R with an emitter 52, a collector 56 connected through a resistance 62 to negative potential - E 2  at terminal 64 and a base electrode 60 which is normally biased below cut-off by positive potential over resistor 58. The negative potential - E 2  provides the biasing voltage for the row switch matrix. In operation, a negative reading pulse applied to the base neutralizes the bias and the transistor conducts, thereby raising the collector electrode potential. The column inverter circuit is shown in Fig. 4 and comprises N.P.N. junction transistors each having its collector 57 connected to positive potential at terminal 55 over a resistor 63, this potential providing the biasing voltage for the column switch matrix. Negative cut-off bias is applied to the base 61 over a resistor 59. Ferro-electric switch matrices. The row switch matrix is shown in Fig. 3, the column switch matrix being similar in design and operation. As previously described, the potentials - E2 and + E2 at terminals 54, 55 of the inverters provide biasing voltages for these matrices. The row matrix has vertical and horizontal input leads 26R, 28R and output leads 10R, the former leads being connected in pairs over resistors 70R to one electrode of a ferro-electric capacitor 74R. The other electrode 77R of each capacitor is connected to a row address lead 10R of the storage matrix and is shunted at a terminal 80R by a parallel circuit comprising a capacitor 76B and resistor 78R, this circuit serving as a voltage divider when the associated ferro-electric capacitor is switched so as to permit the pulse potential to be developed on the selected address lead 10R. Each capacitor 76R is arranged to have less capacitance than the associated ferro-electric capacitor 74R when operating on the vertical part of its characteristic, this requirement ensuring that the major part of the charging voltage appears across the ferro-electric capacitor. When the reading pulses terminate, the ferro-electric capacitor is restored by the bias to its initial polarization state and produces a complementary writing pulse. The pairs of resistors 70R act in series if one lead only is pulsed so that the voltage drop at the ferroelectric capacitor electrode is such that the reversal of polarization state is unable to take place. Specification 790,422 is referred to.