Design of DAC-drivers for resistive actuators

A CMOS digital-to-analog converter which generates the current for directly driving a current-controlled resistive actuator is described. A concept for the design of current sources is introduced. The bias voltage of the source is not kept constant, but is adjusted by a control loop to a value which depends on the output voltage. This technique yields a very large output resistance without imposing heavy limitations on the output-voltage dynamic range. Moreover, fairly small transistors can be used to implement the required current sources. With a 10-V power supply, an actuator with a series resistance of up to ~300 Ω can be directly driven with a full-scale current of ±15 mA, while maintaining a conversion accuracy of 8 b with 1-LSB (least-significant bit) integral linearity