Filters are commonly used in electronic applications to achieve desired performance characteristics. Exemplary filters include high-pass filters, low-pass filters, band-pass filters, and band-stop filters. Each filter type can provide a specific filtering function.
Electrical circuitry utilizing filters include tunable duplexers, phase shifters, tunable matching networks, and reconfigurable power amplifiers. There exists a continuing need for high-quality factor (Q), low insertion loss tunable filtering in these circuits. In RF and microwave applications, for example, placing a sharply defined band-pass filter at a receiver antenna input can eliminate various adverse effects resulting from strong interfering signals at frequencies near the desired signal frequency in such applications.
In communications systems, duplexers provide the ability to receive and transmit signals while using the same antenna. In a typical transmission operation, only signals of a designated transmission frequency are passed to an antenna, which transmits the signal as a radio signal into the air. In a typical receiving operation, a signal received by an antenna is transmitted to the duplexer to select only a signal of the designated frequency. A duplexer uses resonant circuits to isolate a transmitter from a receiver for allowing the transmitter and the receiver to operate on the same antenna at the same time without the transmitter adversely affecting the receiver. Duplexers use filters, such as various pass band filters and notches to accomplish isolation and continuity in signal transfer. In duplexer operation, filters must pass the desired signal while rejecting as much as possible of the undesired signals.
The increased diversity in the functionality of mobile phones has resulted in an increase in the complexity of duplexer design. For example, increased mobile phone functions such as dual mode (e.g., a combination of an analog mode and a digital mode, or a combination of digital modes, such as TDMA or CDMA), and a dual band (e.g., a combination of an 800 MHz band and a 1.9 GHz band, or a combination of a 900 MHz band and a 1.8 GHz band or a 1.5 GHz band) have been increasing the complexity of mobile phone architecture and circuitry. Increased implementation of frequency related functions affect antenna bandwidth. Antenna bandwidth is generally the range of frequencies over which the antenna can operate while some other characteristic remains in a given range. Therefore, increased frequency ranges increase demand for performance over a number of frequency channels, or a wide bandwidth antenna. Moreover, to support these multiple, diverse functions while maintaining proper isolation and reliable signal transfer between transmitter and receiver operations, present communication devices use fixed, redundant circuitry, such as an increased quantity of switches and filters to compensate and broaden duplexer capabilities. Accordingly, such increased use and quantity of filters creates the need for optimizing filter performance.
There is a continuing demand for component reduction and high performance communications devices. Elimination of redundant components, functions, or circuitry is highly desired in communication electronics. Increased performance in communication devices without increasing device size or weight is similarly desirable. Further, there is a continuing need for reliable and quality signal transfer, improved transmitter-receiver isolation, and very high Q value circuitry with respect to duplexers.
Micro-electro-mechanical system (MEMS) technology is currently implemented for various filtering circuitry. Exemplary MEMS components that have been used for filtering include MEMS capacitors. Although there have been improvements in the development of MEMS components for filtering, there is a continuing need for improved performance and stability of these components. Further, there is a demand for improvement in the precision of the capacitance value of MEMS capacitors.
Therefore, it is desirable to provide improved filtering circuitry and related filtering components. Further, there is a need for improved MEMS components for use in filtering circuitry.