A programmable BIST design for PLL static phase offset estimation and clock duty cycle detection

Abstract

Reference spur is a nonlinear effect and important specification in PLL for long term jitter. Periodic events of reference clock create a static phase offset between signals. The finite phase offset comes from charge pump mismatch and layout asymmetry. This paper presents a built-in self-test (BIST) circuit applied for PLL static phase offset (SPO) estimation. The proposed circuit takes advantage of an integrator for time-to-voltage conversion (TVC). Along with comparators and counters, a BIST can be constructed for an estimation of mismatch ratio down to 1% over process corners in simulation (10 psec for lnsec pulse width). The calibration can be operated in a closed-loop PLL with lock signal. Additional circuits including delay lines and non-inverting amplifiers are designed for fast calibration. The result shows at least 27 times faster detection speed can be achieved over process corners. The phase offset between PLL reference and feedback signal is essentially the duty cycle difference, and the test is also applied for duty cycle distortion. Related analysis and measurement are included.