Multi-Stage Charge Pump Design Methodology for Zero-Crossing-Based Amplifiers

The multi-stage charge pump in a zero-crossing-based amplifier (ZCBA) presents complex trade-offs. In this brief, we propose a generalized behavioral model for the ZCBA to quickly predict the optimal charge pump design for a ZCBA based on circuit parameters, without conducting time-consuming transistor-level simulations iteratively. This model enables us to numerically analyze in MATLAB the effects of the circuit parameters, which include the current scaling factor, number of current sources, current value, and input amplitude, on the settling performance including overshoot and settling time. The analysis results conclude that there exists an optimal number of stages that yields the fastest settling time for a given total current and load capacitance. Additionally, the settling time exhibits an asymptotic behavior with respect to the total current. To validate this behavioral model, we designed and simulated a transistor-level ZCBA in a 28-nm CMOS process, demonstrating a good agreement between the model analysis and simulation result.