Design and analysis of a symmetric phase locked loop for low frequencies in 180 nm technology

Design of a stable Phase Locked Loop (PLL) working in MHz frequency range is proposed. Focus of this work is to achieve a symmetric design, where rise and fall time are equal for low operating frequencies. All the blocks of PLL i.e Phase Frequency Detector (PFD), Charge Pump and Loop Filter (CPLF), Voltage Controlled Oscillator (VCO) and Frequency Divider (FD) are carefully designed and integrated. PFD is implemented using D flip-flop and is made to detect minimal phase errors. CPLF has differential design for noise immunity and for avoiding floating conditions. The 15 stage VCO gives frequency range of 30 MHz to 200 MHz for input voltage range of 0.5 V to 1.05 V with a resistor for optimizing linearity. The integrated PLL is stable in the output frequency range of 44 MHz to 200 MHz for given input frequency range of 11 MHz to 50 MHz. The designs are implemented in 180 nm technology and for a supply voltage of 1.8 V.