A tuneable capacitor arrangement for RF use has two series coupled MEMS
variable capacitors (C1,C2;C4,C5,C6,C7), varied according to a control
signal. The series coupling enables the capacitor to withstand a higher
voltage since this is shared by the individual capacitors in a series
coupled arrangement. An increase in size of electrodes for each capacitor
is compensated by a reduction in size of the springs supporting movable
electrodes. These springs can have a larger stiffness value since the
capacitance is larger. This means shorter springs, which can also result
in a reduction in problems of stiction, resistance, and slow switching.
The capacitances have a fixed and a movable electrode, with the RF signal
coupled to the fixed electrode to avoid the springs needing to carry an
RF signal. This can reduce the problems of inductance and resistance in
the springs.