The linearity of analog integrated circuits limits the signal quality in many wireless devices in which the receiver circuits are integrated into a single chip. Consequently, emerging design approaches require to measure and calibrate the linearity of analog/RF circuits, which varies from device to device as a result of manufacturing process variations. This poster presents a method in which the Fast Fourier Transform (FFT) is used to evaluate the linearity of analog circuits for performance optimizations and reliability improvements through the use of on-chip digital processing resources. High frequency requirement for accurate spectral testing of multi-tone signals normally imposes the use of a large number of FFT points that results in high area and power overheads. An accurate and area-efficient FFT method based on the coherent sampling technique is proposed for on-chip analysis of multi-tone signal. Results show that third-order intermodulation (IM3) testing with two tones can be performed with 1.5 dB accuracy for IM3 levels of up to 50 dB below the fundamental tones that are quantized with 10-bit resolution and evaluated with a 16-point FFT.