A 1 MHz bandwidth, 6 GHz 0.18 μm CMOS type-I δσ fractional-N synthesizer for WiMAX applications

A 6 GHz Type-I fractional-N PLL with noise-cancelling DAC and discrete-time sample and hold loop-filter is presented. The 1 MHz bandwidth PLL utilizes an inherently linear PFD and noise-cancelling charge-pump DAC circuit to reduce quantization noise by more than 25 dB. The worst case near-integer in-band spur is measured at -61 dBc and the integrated RMS phase error is -42 dBc. The measured in-band phase noise at 300 kHz offset from the 6.12 GHz carrier is -102 dBc/Hz and out-of-band phase noise at 3 MHz offset is -130 dBc/Hz. The PLL loop settling time for an accuracy of 0.01 ppm and a frequency step of 60 MHz is less than 11 μs. The synthesizer is fabricated in a 0.18 μm CMOS technology with 6 metal layers and consumes 26 mA from a 1.8 V power supply.