Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Patent
1990-03-15
1991-12-03
Scott, J. R.
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
341119, H03M 178
Patent
active
050703315
ABSTRACT:
A monolithic chip with an integrated circuit forming an 18-bit D/A converter powered by a single supply of +5 volts. The circuit includes a voltage reference producing two stable voltages of 3.5 V and 2.5 V which are directed to a control amplifier. This amplifier produces control signals for the current-source cells of a current-steering network utilizing a segmentation decoder for the three most significant bits, a collector-connected R/2R ladder for the intermediate bits, and an emitter-connected R/2R ladder for the remaining least significant bits. The control signals include one for setting the level of current through an NPN current-source transistor, a second for setting the level of current through a PMOS transistor for turning on or off a pair of switching transistors, and a third for establishing a bias voltage for the turn-on circuits for the NPN current-source transistor. An output operational amplifier has its inverting input connected to the output of the current-steering network and to a bipolar offset current circuit powered by the 3.5 V output of the voltage reference. The non-inverting input of the amplifier is connected to the 2.5 volt reference voltage to establish a pseudo-ground for the amplifier. A temperature-compensation circuit is provided for the emitter-connected R/2R ladder, and uses only NPN transistors without requiring any elements interfering with the operation of the current-source transistors, and without requiring an associated amplifier.
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patent: 3940760 (1976-02-01), Brokaw
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patent: 4176344 (1979-11-01), Saari et al.
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patent: 4349811 (1982-09-01), Brokaw
patent: 4543560 (1985-09-01), Holloway
patent: 4800365 (1989-01-01), White et al.
patent: 4899152 (1990-02-01), Barrow et al.
Analog Devices Incorporated
Hoff Marc S.
Scott J. R.
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