Abstract: A track and attenuate (T/A) circuit for use with switched current source DACs is connected across the DAC's differential current outputs. The T/A circuit includes three attenuate switches: first and second single-ended switches which connect the positive and negative sides of the differential output, respectively, to signal ground, and a third, differential switch which connects the positive and negative output lines together. The three attenuate switches are closed simultaneously during a portion of each cycle of the DAC's sample clock, to attenuate the DAC's current outputs while the outputs of the switched current sources are settling—thereby preventing dynamic nonlinearities from being introduced into the differential output current. When properly sized, the three attenuate switches (when closed) reduce the differential output current to near zero and lower the common mode voltage between the positive and negative output lines, significantly improving the DAC's dynamic linearity.

Abstract: A self-trimming current source for used in a switched current source DAC is made from a fixed current source and a variable current source, which are connected in parallel to provide a total output current. The total output current is automatically calibrated by temporarily switching one side of the self-trimming current source to a measurement circuit. Based on the measured value, the variable current source is adjusted to make the total output current equal to a predetermined value. The fixed current source is implemented with a complementary pair of field-effect transistors (FETs) connected in a cascode connection, with the two drain terminals presenting high impedances to the circuitry to which they are connected. A DAC typically includes a plurality of self-trimming current sources, each of which is calibrated during each DAC conversion cycle.