GB1298819A - Digital-analogue converter - Google Patents

Abstract

1298819 Digital-analogue converters TEXACO DEVELOPMENT CORP 18 Dec 1969 [24 Dec 1968] 61798/69 Heading G4H In apparatus for converting to compressed dynamic amplitude analogue form digital signals representing the mantissa A and exponent E in the equation Q= ŒAG<SP>-E</SP>, where G is the radix, the analogue output is of the form Q = Œ(F+A) # . F may have the value (B-1)/(G-B) but in the apparatus described (Fig. 3) (G-B) F = 1, B = G/2 and #(E) = E when E = 1, 2, 3 or 4 and F = 0, B = G/2 and #(E) = 4when E = 5. The apparatus may be used for analysing the signals derived by digitizing seismic signals from geophones. The digital signals in 18 bit floating point coded form (a sign bit, 3 bits representing the exponent and 14 bits representing the mantissa) are stored in register 20. The bits representing the exponent are converted to a signal on one of five leads V 1 -V 5 to control switches SV1-SV5 in a resistor network, the sign bit determining the polarity of the signal applied to the network which generates an analogue output signal having four absolute values (SV4 and SV5 giving the same output). The analogue signal representing 2#<SP>(E)</SP> is fed via amplifier 30 to a ladder network having switches S1-S14 controlled by the 14 bits representing the mantissa. A further switch SO is controlled by the signal on lead V 5 to be connected to the amplifier output when E does not equal 5 and disconnected when E = 5 so that the output of ladder network has the form Q = Œ(1+A)2<SP>-E</SP> for E = 1, 2, 3 and 4 and Q = ŒA2<SP>-4</SP> for E = 4. This signal is fed to oscillograph 32.