GB1195262A - Conversion and Calculating Arrangements Employing Logarithmitic and/or Exponential Relationships between Input and Output Quantities - Google Patents

Abstract

1,195,262. Logarithmic/exponential analoguedigital and digital-digital converter; calculating apparatus. INTELLIGENT INSTRUMENTS Inc. 20 June, 1967, No. 28356/67. Headings G4A and G4H. Analogue-digital and digital-digital converter.-By controlling the frequency of a unijunction transistor relaxation oscillator 99, Fig. 4, (circuit-Fig. 1, not shown) to be proportional to the count in a multi-cathode type counter 100 (Fig. 3, not shown), which also counts the pulses from the oscillator, the count( and the oscillator frequency) will rise exponentially with time, and thus if counting is allowed to continue for a period proportional to x, either by direct control of the oscillator or by a gate between the oscillator and the counter, then the final count will be proportional to e<SP>x</SP>. Frequency control of the oscillator is effected by a feedback form appropriately weighted cathode resistors in the counter. Digital-to-analogue and digital-to-digital conversion is effected by allowing counting 100, Fig. 5, to continue until the count 109 is equal to the digital input 111, and by using the coincidence signal 112 either to gate out the level reached by a linear sawtooth generator 114, or to stop constant frequency clock-pulses 119 passing to a second counter 121, respectively. In both cases the conversion is logarithmic. Exponential digital-to-digital conversion can be effected by inserting a number in counter 121 and by allowing counting to continue in counter 10 (starting from zero) until counter 121 has been stepped backwards to zero by the constant frequency clock-pulses. Calculating apparatus.-The above logarithmic and exponential digital-digital conversions can be used to effect multiplication of division. Thus, for multiplication for example, counting 121 of clock pulses 119, Fig. 6, continues until the count 100 of exponential pulses 99 equals the multiplier 111; then counter 100 is zeroized and counting 121 of clock pulses 99 continues until the count 100 of exponential pulses 99 equals the multiplicand; and finally counter 100 is again zeroized and counting of exponential pulses 99 recommenced until the counter 121 has been stepped backwards to zero by the clock pulses 119. The product then stands in counter 100. Division is similar, the only difference being that counter 121 must count backwards when the divisor is being entered. The quotient, like the product, appears in counter 100.