1. An adaptive voltage scaler (AVS), comprising: at least one delay circuit configured to receive an input signal and delay the input signal by a delay amount relating to at least one delay path of a functional circuit to produce a delay output signal; and an AVS circuit responsive to the delay output signal, the AVS circuit configured to: generate a voltage level setting signal based on a target operating frequency for the functional circuit and delay information in the delay output signal; and increase the delay amount of the at least one delay path to simulate an increased operating frequency for the functional circuit to explore an invalid region of operation of the functional circuit.