Charge pump with reduced current mismatch for reference spur minimization in PLLs

• DOI: 10.1007/s10470-018-1163-z
• Publication Date: 2018-03-17T08:49:48Z
• Authors: Debdut Biswas; Tarun Kanti Bhatt...
• Keywords: Input offset voltage; Minification; Current-feedback operational amplifier

In this article, a charge pump circuit featuring minimal mismatch between its up and down currents is proposed. In conventional charge pumps, where error amplifiers are used in feedback, the factor that hinders exact current matching is the offset voltage of the error amplifier. In the proposed design, the input offset voltage is computed and additional current delivering/comsuming branch is implemented to supplement for the error current. The new charge pump requires a few error amplifiers and a dynamic comparator for its operation. Simulations considering process variations show current mismatch of less than 20 nA even at the worst case event. The proposed charge pump has been utilized in PLL circuits to reduce reference spurs and simulations of these PLLs show remarkable spur reduction.