A 2.4-GHz ISM band delta-sigma fractional-n frequency synthesizer with automatic calibration technique

In the paper, a programmable phase-locked loop (PLL) based ISM band fractional-N frequency synthesizer, commonly used in wireless communication system, is presented. The third order error-feedback Delta-Sigma modulator and high linearity offset phase frequency detector (PFD)/ Charge Pump (CP) are adopted to reduce close-in phase noise due to ΔΣ quantization noise folding. Automatic calibration technique is also introduced to select the optimal frequency sub-band of voltage controlled oscillator (VCO) automatically through process, voltage and temperature (PVT) variation. The Synthesizer is designed in UMC.18µm RF process and has a die size of 1.5mm*2.3mm. The measured phase noise is -112 dBc/Hz at 1 MHz offset.