A 2 GHz 2 Mb/s Semi-Digital $2^{+}$-Point Modulator With Separate FIR-Embedded 1-Bit DCO Modulation in 0.18 $\mu$ m CMOS

A 2 GHz two-point modulator which has a separate high-pass control for DCO modulation is implemented in 0.18 μm CMOS. The proposed modulator with the two-path DCO modulation enables a flexible gain partition for the high-pass and low-pass modulation paths within the DCO and relaxes the DCO nonlinearity with 1-b ΔΣ modulation and embedded finite-impulse response (FIR) filtering. A semi-digital ΔΣ PLL with another FIR filtering in the low-pass modulation enhances PLL linearity with a hybrid loop control. The proposed semi-digital modulator achieves 2.03% RMS EVM with 2 Mb/s GFSK modulation, -132 dBc/Hz phase noise at 3 MHz offset, and -80 dBc reference spur.