Digital to analog converter

Claim 1

A DIGITAL TO ANALOG CONVERTER CIRCUIT COMPRISING AN OPERATIONAL AMPLIFIER HAVING AN INPUT SUMMING JUNCTION, A LADDER NETWORK CONNECTED TO SAID INPUT SUMMING JUNCTION, SAID LADDER NETWORK COMPRISING A PLURALITY OF SERIES CONNECTED RESISTORS, A PLURALITY OF DIGITAL INPUT TERMINALS, A PLURALITY OF COUPLING MEANS A DIFFERENT ONE OF WHICH COUPLES A DIFFERENT ONE OF SAID DIGITAL INPUT TERMINALS TO A DIFFERENT ONE OF THE JUNCTIONS BETWEEN A DIFFERENT TWO OF SERIES CONNECTED RESISTORS, EACH SAID COUPLING MEANS INCLUDING TWO SERIALLY CONNECTED, RELATIVELY OPPOSITELY POLED DIODES CONNECTED BETWEEN A DIGITAL INPUT TERMINAL AND A JUNCTION BETWEEN TWO RESISTORS, A FIRST LOAD RESISTOR, AND A CURRENT SETTING RESISTOR, AND A POWER SUPPLY HAVING A FIRST AND SECOND OUTPUT TERMINAL, MEANS COUPLING EACH SAID FIRST LOAD RESISTOR BETWEEN A DIFFERENT DIGITAL INPUT TERMINAL AND SAID FIRST OUTPUT TERMINAL, AND MEANS COUPLING EACH SAID CURRENT SETTING RESISTOR BETWEEN EACH SERIALLY CONNECTED RELATIVELY OPPOSITELY POLED DIODES AND SAID SECOND OUTPUT TERMINAL, MEANS FOR APPLYING A SIGNAL TO A PREDETERMINED ONE OF SAID DIGITAL INPUT TERMINALS, AND MEANS WITHIN EACH OF SAID COUPLING MEANS RESPONSIVE TO THE APPLICATION OF A SIGNAL TO THE DIGITAL INPUT TERMINAL COUPLED THERETO FOR APPLYING A PREDETERMINED CURRENT TO THE JUNCTION COUPLED THEREBY TO CAUSE A VALUE OF CURRENT TO FLOW THROUGH SAID SUMMING JUNCTION AS DETERMINED BY THE RESISTANCE VALUE OF THE SERIES CONNECTED RESISTORS ON EITHER SIDE OF THE JUNCTION OF RESISTORS TO WHICH SAID PREDETERMINED CURRENT IS APPLIED.