Patent GB-988039-A (GB)
Title: Improvements in or relating to computer devices
IPC: G06J1/00
Filed: 1963-06-06
Abstract: 988, 039. Electric selective signalling systems. ROCHAR ELECTRONIQUE. June 6, 1963 [June 6, 1962; June 18, 1962], No. 22541/63. Heading G4H. A digital representation of the logarithm of a number represented by an amplitude significant voltage is obtained by comparing the input voltage with selected voltages from a set of reference voltages with known logarithms and by displaying the logarithm of that reference voltage which is nearest the input voltage. As described the input voltage U, Fig. 1, attenuated A1, A2, by a factor of 1 or . 01 to bring it within the range 1 to 10 volts, is applied 25 to a comparator 24 to which is also applied 27 a reference voltage V A  which is selectively attenuated A 3 . . . A 14  so as to balance the input voltage. Those attenuators required to be in circuit to produce a balance provide a digital indication, in "1, 2, 2, 4" coded decimal form, of the logarithm of the input number. The sequence of operations to effect a balance is controlled by a clock 46 and is as follows: Initially relays 18, 22, 30. . . 34 are all de-energized, attenuators A1, A2 are bi-passed by contacts 18a, 22a and attenuators A3. . . A 14  are in circuit. The clock 46 energizes relays 18, 22, 30.. . 34 sequentially and each relay holds unless it is immediately reset by a pulse from comparator 24 via switches 40 and 42, which is only produced when the attenuated input voltage 25 is less than the known voltage 27. Thus at the first step relay 18 is energized thereby putting attenuator A1 in circuit and if this results in the voltage 25 being less than the voltage 27 then the relay 18 is reset and attenuator A1 is again bipassed. The second step is similar. At the third step relay 30 is energized thereby bi-passing attenuator A3 and if this results in the voltage at 27 becoming larger than the voltage at 25 then relay 30 is reset and attenuator A3 is put back in circuit. Subsequent steps are similar and the attenuators are such that the relays which are still energized at the end of the sequence produce, by contacts 18c, 22c, 30c. . . 34c, a digital representation of the logarithm of the input number. The relays also have further contacts which by switching in appropriate reference voltages produce 52 an amplitude significant voltage also representing the logarithm. Since the number represented digitally by relays 30. . . 34 at the end of the sequence is the logarithm of the voltage at 27, it follows that if the number represented digitally by relays 30. . . 34 is x then the voltage 27 is 10<SP>x</SP>. This fact is exploited in Fig. 2 where an unknown voltage A is digitised by a conventional balancing technique and the digital output on relays 59, 61, . . . 63, 65 is used to control attenuators A 1  A 2 . . . An so that a voltage representing 10<SP>A</SP> is produced at 81. Thus the circuit of Fig. 2 produces the antilog of an input number represented by an amplitude significant voltage. By combining the circuits of Figs. 1 and 2 multiplication and evolution can be performed. The relays can be electromagnetic or semi-conductor devices.