Circuitry and a method for testing oversampled Analog to Digital converters. The voltage reference is used as the input signal, thus eliminating the need for a special signal generator. The dynamic signal is obtained by not sampling the voltage reference on every sample. Instead, a state machine is used to gate the sampling of the voltage reference, which in turn causes a varying amount of change to be injected into the first integrator in the converter. As a result, the state machine effectively simulates many input levels.