Varactor (or “varicap”) diodes are used primarily in radio-frequency (RF) circuits to provide a capacitance that can be varied by changing the applied voltage. These types of diodes often are used for tuning circuits, such as RF oscillators and filters found in wireless applications like wireless microphones and radios. Designers, then, should know about the benefits of using a nonvolatile digital-to-analog converter (DAC) to provide the biasing voltage of a varactor diode used as a voltage-controlled capacitor. The varactor diode is operated under reverse bias, which creates a depletion zone around the P-N junction. Changing the level of the reverse bias changes the thickness of the depletion region and, thus, the effective capacitance of the diode. Increasing voltage causes a decrease in capacitance. Varactor diodes are specified with a nominal capacitance value and the range of capacitance that can be achieved with a maximum and minimum voltage level. Increasing the bias voltage ran...