Multi-mode fractional-N synthesizer with a stabilized loop bandwidth

To solve the problem of stability of the multi-mode frequency synthesizer during mode transitions,a method of stabilizating the loop bandwidth is presented by means of calibrating the charge pump current according to the divider ratio. The method makes the variation of the loop bandwidth to be kept within a smaller range at different division ratios. A multi-mode fractional-N synthesizer adopting the method can work stably in seven modes of three positioning systems.Simulation results show that the variation of normalized I_CPK_VCO/ω_VCO in seven modes is in the range of -3.3％ and 3.3％. For each mode, the in-band and out-of-band phase noises are not larger than -93dBc/Hz and -119dBc/Hz, respectively. The setting time is less than 24μs. The total power consumption is 15.21mW at 1.8V voltage supply.