A method, circuit, and computer program product for receiving a first intermediate signal that is at least partially based upon a first reference signal. A second intermediate signal is received that is a time-shifted version of the first intermediate signal. An output signal is generated that is based upon the difference between the first intermediate signal and the second intermediate signal. An anticipated differential change in the output signal is determined, the anticipated differential change to occur based upon a transition in the first reference signal. A realized differential change in the output signal is measured, the realized differential change occurring based upon a transition in the first reference signal. The realized differential change in the output signal is compared to the anticipated differential change in the output signal to determine a nonlinearity indicator.