A Waveform Distortion Correction Method Based on Jitter Injection and FIR Digital Filter Using Farrow Structure

Direct digital frequency synthesis (DDFS) technology is widely used in modern nanoscale CMOS integrated devices, but it suffers from large waveform distortion and timing jitter in applications. In order to achieve high frequency resolution with limited waveform memory capacity, the phase of the waveform is usually truncated to switch waveform phases. The truncation of the phase causes the synthesized waveform to produce spurious and loses waveform details during phase switching, resulting in waveform distortion. In this paper, we propose a waveform distortion correction method that combines jitter injection and FIR digital filter using Farrow structure. Based on the waveform real-time computation technique, jitters are injected into the waveform time parameter to break the harmonic components caused by non-integer multiples of the sampling rate and waveform frequency. Using this approach, waveform spurious is further suppressed. The waveform distortion correction is achieved by design functions which complement the waveform distortion features. The complementary functions are then combined as Farrow filter coefficients by polynomial fitting. In this paper, a pulse waveform with 0.2 ps timing resolution is generated at 1 GSPS sampling rate by real-time computation technique. And then the waveform distortion correction method based on the proposed jitter injection combined with Farrow structure reduces the deterministic jitter from more than 600 ps to less than 20 ps, and the random jitter from more than 60 ps rms to less than 25 ps rms. The accuracy of timing parameters such as rise time, fall time, and pulse width is improved from ±500 ps to ±50 ps.