Patent ID: 6417793
Filing Date: 2002-07-09
Classification: H03M

Abstract:
A switched current source digital-to-analog converter (DAC), comprising:an array of current sources which produce respective output currents, an array of switches which are connected to switch respective ones of said current source outputs to one of a complementary pair of output lines in response to respective control signals to provide a differential output current on said complementary pair of output lines, a controller which receives a digital input word representing a desired differential output current and a sample clock at respective inputs and which provides said control signals to said switches to produce said desired differential output current, said controller arranged to operate said switches once per cycle of said sample clock, said differential output current settling within a predetermined time period after said switches have been operated, and a track and attenuate (T/A) circuit, said T/A circuit comprising: a first attenuate switch which connects one of said complementary output lines to a signal ground when closed in response to an attenuate signal, a second attenuate switch which connects the other of said complementary output lines to signal ground when closed in response to said attenuate signal, a third attenuate switch which connects said complementary output lines together when closed in response to said attenuate signal, and an attenuate switch drive circuit arranged to produce said attenuate signal such that each of said attenuate switches is closed during said predetermined settling time to attenuate said differential output current while said differential output current is settling.