a high dynamic range digitally-controlled oscillator (dco) for all-digital pll systems

in this paper, a new high dynamic range digitally-controlled oscillator (dco) for all-dpll systems is proposed. the proposed dco is based on using a δς modulator as a digital-to-analog converter. using δς dac can provide a very high resolution (18-bit) control on the dco. the δς dac output is a 2-level pulse signal that needs to be filtered for cancelling the out of band shaped noise. the used δς modulator is a 4th order mash δς modulator working with the osr of 128 and the sampling frequency of 450mhz. the proposed dco is used in a pll to synthesize the frequency in the range of 1700mhz to 1800mhz for gsm-1800 application. the achieved phase noise for this pll based synthesizer in whole the range is -115 dbc/hz at the offset frequency of 500 khz. the designed adpll including the dco is simulated in ads with 0.18µm cmos technology.