A low-cost, leakage-insensitive semi-digital PLL with linear phase detection and FIR-embedded digital frequency acquisition

A semi-digital PLL utilizing a hybrid DCO is presented. A mixed-mode loop control with an analog proportional path and a digital integration path provides linear phase tracking, leakage-insensitive loop filtering, and technology scalability. With the absence of the linear TDC, the semi-digital PLL with the hybrid DCO can relax design difficulties such as achieving low power or requiring an advanced CMOS technology. Also, the hybrid finite-impulse response (FIR) filtering method is employed to reduce the DCO quantization noise without causing latency. The prototype PLL implemented in 0.18 μm has the active area of 0.6 mm² where only 0.01 mm² is occupied by the analog loop filter.