Isolated digital-to-analog converter

Claim 1

A highly isolated digital-to-analog converter for converting data received at a plurality of digital input terminals to an analog output signal comprising: AC data isolation coupling means for coupling the digital input signals into the converter; first and second differential amplifier means arranged in a balanced differential configuration each including an input summing junction, an input reference terminal and an output terminal, for generating an analog signal across said output terminals; a plurality of switching stages, each stage coupled to an associated digital input terminal by said isolation coupling means, and including a balanced pair of transistor switching devices and a balanced pair of resistive elements, each said stage arranged to be coupled between the summing junctions of said first and second amplifier means in response to a digital signal at its associated input terminal; an output load having a first terminal and a reference terminal; high-frequency impedance means coupling the output terminals of said amplifiers with the first and reference terminals of the output load for preventing high frequency input leakage current from flowing through the load; said balanced differential configuration preventing common-mode voltages from inducing differential voltages across the load, whereby either output terminal of said amplifiers may be connected to the reference terminal of the load without affecting the common-mode rejection response of the converter.

Claim 10

A system for converting digital data into an analog voltage form comprising: a plurality of digital input terminals; switching means including first and second complementary conductivity type transistors driven in the inverted mode, one said switching means associated with each input terminal; AC data isolation means including shielded transformers coupled to each input terminal for operating said switching means in accordancE with signals on their associated input terminals; first and second operational amplifiers arranged in a balanced differential configuration, each including an input summing junction, an input reference terminal and an output terminal, for generating an analog signal across said output terminals; an output load having a first terminal and a reference terminal; high-frequency impedance means including a balun coupling the output terminals of said amplifiers with the first and reference terminals of the output load for preventing high frequency input leakage current from flowing through the load; a source of input AC power; AC power isolation means including a shielded transformer for coupling the power source to the input of a reference voltage source, said reference source supplying bias potentials to the reference input terminals of said amplifiers and bias current to the summing junctions of said amplifiers; a set of first and second balanced resistors associated with each digital input terminal and coupled between said first and second operational amplifiers, respectively, and the output of said first and second transistors, respectively, said first and second resistors connected in series relationship with each other between the summing junctions of said amplifiers when said transistors are operated and in parallel with the so-connected sets of resistors associated with other digital input terminals; said balanced differential configuration preventing common-mode voltages from inducing differential voltages across the load, whereby either output terminal of said amplifiers may be connected to the reference terminal of the load without affecting the common-mode rejection response of the converter.

Claim 11

A system for converting digital data into an analog voltage form comprising: a plurality of digital input terminals; switching means including first and second complementary conductivity type transistors driven in the inverted mode, one said switching means associated with each input terminal; AC data isolation means including shielded transformers coupled to each input terminal for operating said switching means in accordancE with signals on their associated input terminals; first and second operational amplifiers arranged in a balanced differential configuration, each including an input summing junction, an input reference terminal and an output terminal, for generating an analog signal across said output terminals; an output load having a first terminal and a reference terminal; high-frequency impedance means including a balun coupling the output terminals of said amplifiers with the first and reference terminals of the output load for preventing high frequency input leakage current from flowing through the load; a source of input AC power; AC power isolation means including a shielded transformer for coupling the power source to the input of a reference voltage source, said reference source supplying bias potentials to the reference input terminals of said amplifiers and bias current to the summing junctions of said amplifiers; a set of first and second balanced resistors associated with each digital input terminal and coupled between said first and second operational amplifiers, respectively, and the output of said first and second transistors, respectively, said first and second resistors connected in series relationship with each other between the summing junctions of said amplifiers when said transistors are operated and in parallel with the so-connected sets of resistors associated with other digital input terminals; said balanced differential configuration preventing common-mode voltages from inducing differential voltages across the load, whereby either output terminal of said amplifiers may be connected to the reference terminal of the load without affecting the common-mode rejection response of the converter.