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.