US Patent 7489428 - Variable threshold MEMS array actuator

http://www.freepatentsonline.com/7489428.html

For multi-gradation effects it is difficult to implement MEMS-based micromirrors formed from interferometric ribbons in an analog mode. This patent from IDC (now being developed by Qualcomm) teaches an alternative solution based on a halftone method. Claim 1 reads:

1. A MEMS device, comprising:

a plurality of elements having differing values of at least one of a time-based activation threshold for a select voltage and a voltage-based activation threshold for a select time; and

addressing lines configured to provide signals of at least one of selectable voltage and selectable time to the elements such that different numbers of elements activate in a selectable manner, according to the voltage and time of the signals.