A spectral leakage-driven loopback method for predicting performance of a mixed-signal circuit. The method includes generating, by an on-chip Digital Signal Processor (DSP) core, a digitally-synthesized single-tone sinusoidal stimulus. A nonlinear digital-to-analog-converter (DAC) channel is sampled. A DAC output signal is supplied to a nonlinear analog-to-digital converter (ADC) channel through an analog loopback path. Each of the DAC channel and the ADC channel are measured for a production testing. The on-chip DSP core performs postprocessing and predicting harmonics of the two individual DAC and ADC channels.