A Very High Linearity Twin Phase Interpolator With a Low-Noise and Wideband Delta Quadrature DLL for High-Speed Data Link Clocking

A twin phase-interpolator (PI) architecture cancels most of the deterministic phase nonlinearity and achieves very high linearity across a wide frequency range with only four-phase input clocks. A delta quadrature delay-locked loop (Delta QDLL) is further proposed that generates wideband, low-jitter, and accurate quadrature clocks from the delay difference of two paths with a background analog quadrature tuning loop. A 1.2-V 65-nm CMOS prototype has a Delta QDLL with a quadrature accuracy of 0.9° from 3.5 to 11 GHz across ten chip samples. It consumes 7.8 mW at 7 GHz and has a 48.1- $\mathbf {fs}_{\mathbf {rms}}$ jitter, yielding an outstanding figure of merit of −257.4 dB. The 7-bit twin PI achieves a less-than-1.45-LSB peak-to-peak integral nonlinearity ( $\mathbf {INL}_{\mathbf {pp}}$ ) from 3.5 to 11 GHz and the lowest $\mathbf {INL}_{\mathbf {pp}}$ of 0.72 LSB at 7 GHz. The PI has a 58.5- $\mathbf {fs}_{\mathbf {rms}}$ jitter for a fixed PI control code. At 7 GHz with −1429-ppm clock modulation, the integrated fractional spur is as low as −41.7 dBc.