In today’s cell phones, small improvements can make a big difference in battery life — or cost. A Microelectromechanical System (MEMS) approach could provide improved impedance matching and a definite value to cell phone makers. Using MEMS technology, an ultra- small, tunable capacitor provides dynamic impedance matching that translates into lower power consumption.
Transmitted power is an important consideration for improving cell phone efficiency. While the phone is designed to be a perfect 50-ohm system under nominal circumstances, the power amplifier’s output and the antenna’s input are hardly ever perfectly matched in actual usage. To cope with a low signal level, the power amplifier’s output increases to the point where it cannot increase any further and finally the cell phone drops the call. The problem is impedance mismatch, so a technique to dynamically match the front-end components would allow much more efficient power transfer. This is an ideal place for MEMS technology, due to its dynamic ability to get input from the environment and determine if impedance needs to be added or subtracted from the network to achieve a 50-ohm system.
The MEMS capacitor is created by using surface micromachining to etch a capacitor plate in a multi-layer semiconductor structure. Using this process, the multi-throw tunable capacitors created by WiSpry Inc. initially range from 1 and 2 , but can be scaled to as high as 20 pF or more. Units have a quality factor (Q) of about 100 at 2 GHz and self-resonant frequency greater than 5 GHz.
These small capacitance values make a big difference in system performance. “You can actually get back a very large amount of savings that way in terms of whole dBs of loss,” says Jeffrey Hilbert, president and CEO of WiSpry. “That roughly translates into 10, 15 or 20 percent extra battery life.” With reduced power consumption, a cheaper, thinner battery can be used for a low-end phone, more features can be added to a high-end phone and other options exist for products between these extremes.
For more information on the WiSpry tunable capacitor, go to http://www.wispry.com/prdcts_capacitors_rf.htm