An adaptive low power DC-DC converter concept for PLL controlled tuning of RF circuits

This paper describes a DC/DC converter intended to generate the required reverse voltage for varicap diodes used in RF resonance circuits. As its primary purpose is use in consumer RF products, the proposed design, operating from 5 V, was optimized for low cost. Close proximity to sensitive RF circuitry requires DC/DC converter operation with minimal radio frequency interference. Therefore, instead of using a switching type regulator, the proposed design uses a sinusoid signal with a frequency of about 250 kHz that is stepped-up to the required amplitude by an impedance transformation using an LC resonance circuit. A double wave rectifier converts the AC signal to a DC voltage. A basic idea underlying the converter design is that interference can be kept within limits by minimizing the amount of power to be delivered to the load.