A fractional-N synthesizer for multi-mode positioning system with constant loop bandwidth

A fractional-N frequency synthesizer with constant loop bandwidth is presented. This synthesizer can be applied to the multi-mode positioning receiver with seven modes in three positioning systems. In all seven modes it has constant loop bandwidth and can work stably by using the improved adjusting method in charge pump biasing current and the linear varactor in VCO (voltage-controlled oscillator). Simulations show that this synthesizer meets the requirements of high performance receiver. For each mode, the in-band and out-of-band phase noises are not lager than -95dBC/Hz and -119dBC/Hz@1MHz, respectively. The variation of normalized I cp K vco/wvco in seven modes is in the range of -8% and 7%. The setting time is less than 21μs. The total power consumption is 15.34mW at 1.8V voltage supply.