A 1.75 mW 1.1 GHz Semi-Digital Fractional-N PLL With TDC-Less Hybrid Loop Control

A 1.1 GHz semi-digital fractional-N PLL without the time-to-digital converter (TDC) whose resolution and linearity heavily depends on process and temperature variations is implemented in 65 nm CMOS. A hybrid loop control with a fully differential proportional-gain path and embedded finite-impulse response (FIR) filtering achieves linear phase tracking as well as good technology scalability, having a small analog loop filter area less than 0.01
${\rm mm}^{2}$
. The use of the hybrid FIR filter not only suppresses out-of-band quantization noise of the
$\Delta\Sigma$
modulator but also improves the linearity of the proportional-gain path. The TDC-less semi-digital PLL consumes 1.75 mW from a 0.9 V supply voltage, achieving significant power reduction compared to conventional all-digital PLLs.