efficient calibration of circuits is performed using injection imprecise voltage by using different voltages in a subtractive manner to be able to calibrate with respect to a voltage that is out of a desirable measurable range using measuring circuitry . efficient background calibration of circuits is also achieved by providing an equivalent circuit element to circuit elements receiving an injected calibration signal , and switching circuit elements . such imprecise voltages can be determined through such calibration , and then used to calibrate a second circuit generating the imprecise voltages .