SELF-TRIMMING CURRENT SOURCE AND METHOD FOR SWITCHED CURRENT SOURCE DAC

摘要

A self-trimming current source for used in a switched current source DAC is made from a fixed current source (26) and a variable current source (28), which are connected in parallel to provide a total output current (Itot0). The total output current is automatically calibrated by temporarily switching one side of the self-trimming current source to a measurement circuit (30). 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) (N3, P4) connected in a cascode connection, with the two drain terminals presenting high impedances to the circuitry t 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.