Embedded servo loop for ADC linearity testing

A novel embedded servo loop is proposed for testing the differential nonlinearity (DNL) and integral nonlinearity (INL) of analog-to-digital converters (ADCs). An integrator whose integration time is precisely controlled by a delay line is the key part of the servo loop circuitry. The analog part of the servo loop is very simple and does not need calibration while the digital part can be synthesized from a hardware description language. The servo loop does not alter the architecture and operation of the ADC under test and can be used to test any kind of ADC. The servo loop occupies a small area and is suitable for built-in self-test application. The measurement results for DNL and INL are transformed into a digital representation, and the measurement resolution and error are determined by the delay of standard digital gates. Simulation results are reported for an embedded servo loop implemented in 0.35μm CMOS technology.