Phase Locked Loop (PLL) tuning circuitry is a common solution for stabilizing tuning frequency in Radio Frequency (RF) circuits. In order to maintain the frequency of a PLL circuit within very tight limits a calibration process may be carried out, which is able to compensate for variances in the electrical features of the tuning circuitry components over time and frequency. In particular, when the component used in the PLL circuit to change the PLL frequency is a voltage controlled capacitor (varactor), it may be desirable to compensate for the tuning sensitivity of the varactor to changes in its electrical features over frequency (also defined “tuning linearity”). For improved linearity in a tuning circuit it may be desirable to compensate the tuning linearity also for variance due to other factors, such as temperature.
Metal Oxide Semiconductor Field Effect Transistor (MOSFET) varactors (also known as MOSCAPs) are regarded as inferior to bi-polar varactors with respect to tuning linearity, yet MOSCAPs are generally capable of handling dual-polarity voltage swing while bi-polarity varactors are not generally capable of doing so.
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