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Gain-Boosting Charge Pump for Current Matching in Phase-Locked Loop

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2 Author(s)
Y. -S. Choi ; Div. of Electron., Comput., & Telecommun., Pukyong Nat. Univ., Busan ; D. -H. Han

The charge pump (CP) circuit is a key element in a phase-locked loop (PLL). Its function is to transform the Up and Down signals from the phase/frequency detector into current. In CMOS CPs, which have Up and Down switches made of p-channel MOS and n-channel MOS, respectively, a current mismatch occurs when dumping the charge to the loop filter. This current mismatch of the CP in the PLL generates fluctuations in the voltage-controlled-oscillator input and subsequently, a large phase noise on the PLL output signals. In this brief, a new CP with good current matching characteristics is proposed. By using a simple gain-boosting circuit, good current matching characteristics can be achieved with less than 0.1% difference of the Up/Down current over the CP output voltage ranges of 0.8-2.2 V and 0.5-1.2 V on 0.35-mum 3.3-V and 0.18-mum 1.8-V CMOS processes, respectively. The proposed CP circuit is simulated and verified by HSPICE with 0.35-mum 3.3-V and 0.18-mum 1.8-V CMOS parameters

Published in:

IEEE Transactions on Circuits and Systems II: Express Briefs  (Volume:53 ,  Issue: 10 )