Thomas S Guy

US Patent:

50103377, Apr 23, 1991

Filed:

Mar 15, 1990

Appl. No.:

7/493997

Inventors:

Shinichi Hisano - Boston MA
Thomas S. Guy - Andover MA

Assignee:

Analog Devices, Incorporated - Norwood MA

International Classification:

H03M 178

US Classification:

341154

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. 5V and 2. 5V 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. 5V output of the voltage reference.