Time-to-voltage converter for on-chip jitter measurement

In this paper, we present the concept and design of a time-to-voltage converter (TVC), and demonstrate its application to on-chip phase-locked loop (PLL) jitter measurement. The TVC operates in an analog, continuous mode without using a sampling clock. It compares the signal under measurement with a reference signal by charging and discharging a capacitor. First, the low-frequency reference signal charges the capacitor in one cycle. Then, the jitter signal discharges the same capacitor repeatedly until the voltage on the capacitor falls below a threshold. The number of times the jitter signal needs to discharge the capacitor is recorded on a binary counter. We demonstrated that a 160-ps injected jitter is successfully measured by the proposed TVC with a 2-MHz reference signal. We also demonstrated the successful measurement of a 14-ps average PLL jitter, without jitter injection. An 8% measurement error is found in both experiments, using four-bit counters. Finally, we analyze the relations between design parameters and show trade-offs between measurement resolution and measurement time.