A high swing charge pump with current mismatch reduction for PLL applications

Abstract

A charge pump (CP) is widely used in modern phase-locked loop (PLL) implementations. The CP current mismatch is a dominant source of static phase offset and reference spur in the PLL output signals. In this paper, a novel CP with small current mismatch characteristic over a wide output voltage range is proposed. The specially designed dual compensation circuits use the unity-gain feedback operational amplifier and current mirrors to reduce the current mismatch when the output voltage is closed to the supply voltage (V DD) or ground (GND). And the additional feedback transistors are used to reduce the impact from the channel length modulation effect. Post-layout simulation results demonstrate that the output current of the proposed CP in a 40 nm CMOS technology is 115 μA. Moreover, the current mismatch is less than 0.97 μA or 0.84% over the output voltage range from 0.04 to 1.07 V covering more than 93.6% of the 1.1 V supply. Thus, the proposed CP maximizes the dynamic range, and reduces the phase offset and reference spur of CP-PLLs.

A design of low mismatch charge pump with feedback compensation current

“…The low mismatch structure in literature [10] introduces unity-gain buffer in the feedback loop as voltage following and current isolation. However, the optimized circuit designed in this paper is only realized by six MOS tubes without the use of unity-gain buffer, which can guarantee the current matching performance and greatly reduce the circuit power consumption and layout area.…”

A 0.7V 1.6mW fractional-N synthesizers for BLE RF transceiver in 40nm CMOS

“…High-performance CP design is another challenge under the low voltage supply, the reference spur is mainly induced by the non-ideal effects of CP and phase and frequency detector (PFD) circuit. In general, the cascode operation amplifier and negative feedback technique are used to guarantee the charging and discharging current matching in the conventional charge pump circuit [16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]. However, the threshold voltage does not decrease with the voltage supply [30], resulting in the efficient operating voltage range of the charge pump becoming narrower.…”