Replica compensated linear regulators for supply-regulated phase-locked loops

Supply-regulated phase-locked loops rely upon the VCO voltage regulator to maintain a low sensitivity to supply noise and hence low overall jitter. By analyzing regulator supply rejection, we show that in order to simultaneously meet the bandwidth and low dropout requirements, previous regulator implementations used in supply-regulated PLLs suffer from unfavorable tradeoffs between power supply rejection and power consumption. We therefore propose a compensation technique that places the regulator's amplifier in a local replica feedback loop, stabilizing the regulator by increasing the amplifier bandwidth while lowering its gain. Even though the forward gain of the amplifier is reduced, supply noise affects the replica output in addition to the actual output, and therefore the amplifier's gain to reject supply noise is effectively restored. Analysis shows that for reasonable mismatch between the replica and actual loads, regulator performance is uncompromised, and experimental results from a 90 nm SOI test chip confirm that with the same power consumption, the proposed regulator achieves at least 4 dB higher supply rejection than the previous regulator design. Furthermore, simulations show that if not for other supply rejection-limiting components in the PLL, the supply rejection improvement of the proposed regulator is greater than 15 dB.