Performance Comparison of Capacitive Stacking Techniques for Radio Frequency Mixers

This paper presents an analysis of three capacitive stacking techniques in a bottom-plate N-path mixer, which are the Dickson charge pump, Series-Parallel charge pump and Fibonacci charge pump. The three charge pump circuits are compared in a DC-DC application and in a Radio frequency mixer. The performance of the charge pumps is derived based on the voltage gain, taking into account the effects of parasitic capacitances and the on-resistance of the switches in the charge pump. The Dickson and Fibonacci charge pump with passive mixer have shown similar behaviour, both have a decrease in voltage gain around 29% when parasitic capacitance are taken into account. The Series-Parallel charge pump with passive mixer is influenced the most by the effects of the parasitic capacitance with a voltage gain decrease of 70.5%. This decrease in voltage gain is most likely caused by the contribution of the parasitic capacitance in the charge pump to the unwanted low pass filtering in the mixer. A switch on-resistance in the charge pump which is 10 times larger than the switch on-resistance in the mixer is analysed. Due to the increase in switch on-resistance a decrease in voltage gain of 30.8%, 38.3% and 66.4% has been observed for the Dickson, the Fibonacci and the Series-Parallel charge pump, respectively. Index Terms—Switched Capacitor, Charge Pump, N-Path Mixer/Filter, Mixer-First Receiver.