Digital to Analog Conversion

1,194,307. Digital/analog converters. INTERNATIONAL BUSINESS MACHINES CORP. 7 March, 1969, No. 12061/69. Heading G4H. From a constant current source 10, binary weighted currents are derived by transistors 18, 19, 20, 21, 22 having binary weighted emitter areas, these currents being fed to emitter coupled transistor pairs 24, 25; 26, 27; 28, 29; 30, 31; 32, 33; a binary coded input bit being fed to the base of one transistor 24, 26, 28, 30, 32 in each pair so that an analogue signal representing the digital input signal is fed to a load 13. If the input bits have value n then with the 5 bit converter shown by summing the output currents from the collectors of transistors 25, 27, 29, 31, 33 a current 31-n is fed to a second load 14. The converter is preferably in integrated circuit form, suitable layout for the converter being given (Figs. 2 and 3, not shown).