Authors: M. Innocent, P. Wambacq, S. Donnay, H. Tilmans, M. Engels, H. DeMan and W. Sansen
Affilation: IMEC, Belgium
Pages: 234 - 237
Keywords: MEMS, varicap, resonator, nonlinear, Volterra series
Today’s wireless communication systems often require a high linearity for the RF building blocks. One of these blocks can be a tunable LC filter using MEMS variable capacitors (varicaps). In these filters, the varicaps are the largest contributors to the nonlinearity. Therefore we analyze the frequency and bias dependence of the linearity of a MEMS varicap. Our analysis shows that two high frequency tones can only generate large unwanted intermodulation products in a MEMS varicap if they are close to each other. When the tones are widely separated, the nonlinear distortion can be much smaller than for other varicaps like MOS structures or junction capacitors. When the varicap is used in an LC tank (which is building block for a filter), the linearity of that tank decreases with increasing tank quality factor. This implies there is a trade-off between the linearity of a tunable LC filter and its selectivity and loss.
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