RF circuitry plays a crucial role in the success of modern wireless communications. The linearity of RF devices, such as the power amplifier studied in this paper, is the key in determining the overall system performance. In communication systems adopting Orthogonal Frequency-Division Multiplexing (OFDM), non-ideal effects are summarized by the measurement of the Error Vector Magnitude (EVM). During the process of circuit design, it is desirable yet very time-consuming to include in simulations the EVM test by inputting pseudo-random OFDM signals. To speed up the simulation, a specially designed broadband signal is developed with certain spectral and statistic properties while maintaining a short length. By using the designed signal, the simulation time can be drastically reduced with accurate EVM results as compared to using lengthy pseudo-random OFDM signals.