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A complete equivalent model and analysis of high-efficiency charge-pump gain-increase (PGI) circuits with resistive loads are proposed. Based on this simple analytical model, the characteristics of PGI circuits can be approximately predicted and several handy equations, which are useful for pencil-and-paper design, can also be found for planning the desired circuit to achieve good enough performance with an acceptable accuracy tolerance in the steady state. In addition, an optimized design method for PGI circuits with resistive loads is developed in terms of the total number of gain stages in the design and the ratio between pump capacitors. For 1.5 V supply voltage operation, reliability and accuracy are demonstrated by comparisons between SPICE simulations of the PGI circuit and the results from the equivalent model. The model also has been validated by means of measurements taken from a test chip and typically shows relative open-loop output voltage errors lower than 8%. Finally, although the derivation of the model was based on a PGI circuit, it is shown that the design strategy can also be applied to other charge pump designs that have no voltage drop between the inner stages and the output stage.