144#WIDEBAND SIGMA DELTA MODULATOR

ABSTRACT

Wide band Sigma-Delta PLL modulator is based on PLL fractional N synthesis techniques along with Sigma-Delta modulation to randomize fractional N spurs. A modified Sigma-Delta function allows for suppression of Sigma-Delta noise at low frequencies & hence allows wider bandwidth. This is achieved using a fractional-N PLL architecture. They are capable of synthesizing frequencies at channel spacings less than the reference frequency. This helps to increase the reference frequency & hence reduces PLL’s locking time.

One of the major disadvantages of fractional-N PLL is the generation of high tones at multiples of channel spacings. Using digital Sigma-Delta modulation techniques in fractional-N PLL frequency synthesis eliminates this spurs. This is achieved by randomizing the feedback division ratio such that the quantization noise of the fractional-N PLL is transferred to high frequencies. Main advantages of this techniques are small frequency resolution, wide tuning bandwidth &fast switching speed. Low power & low area techniques are used in modified Sigma-Delta modulator. It has a total power consumption of 2mW & 1-GHz operation.