Image Number 3 for United States Patent #8456338.
A source-measure unit (SMU) may be implemented with respective digital control loops for output voltage and output current. The digital control loop associated with the output that is being regulated may be the setpoint control loop while the digital control loop associated with the other output may be the compliance control loop. The digital loop controller may switch between the setpoint control loop and the compliance control loop without generating a mode-change glitch, by maintaining a single integrator. The compliance methods may differ in how and when the decision is made to select which of the measured signals provides the error signal to the integrator. Thus, there may be no issue with integrator wind-up, which might be the case if there were two complete control loops operating continuously.