CkBooks Online – Free Online Books

In the most general case, there are at least two types of tuning needs to be considered in RF/microwave circuits and systems. First, one might be interested in changing the frequency-determining parameters of a circuit/system, designed originally to operate in a given frequency band, so that it can operate at a different frequency band. An example of this would be a filter operating in a multiband wireless handset, whose response could be switched back and forth so that it could operate in two or more frequency bands.

Second, one might be interested in controlling the frequency-determining parameters of a circuit/system so as to optimize its performance, which may well include switching among bands, but more interestingly would include enabling the adaptive control of the circuit/system so that it can meet a certain error function, predicated for instance, upon the real-time insertion loss, return loss, power efficiency, or harmonic level. The binary-weighted capacitor and inductor arrays [10] shown in Figures 4.3 and 4.4 were devised with these scenarios in mind.

In the binary-weighted capacitor array, the noninvasive properties of MEM switches are exploited to reconfigure networks of elementary unit capacitor cells ,so that the overall network realizes a certain capacitance. Thus, in essence, the approach discretizes the top plate area of the overall capacitor so that any value of capacitance, in steps of the unit capacitor cell value, may be set by opening or closing appropriate switches.

Thus assuming each unit capacitor cell has a value C, then to obtain an overall network capacitance of 2C, the switches S3 and S4 would be closed, while the switches S1, S2, S5, S6, S7, S8, S9, and S10 would be open. To obtain a network capacitance of 4C, the switches S6, S7, S8, S9, and S10 would be closed, while the switches S1, S2, S3, S4, and S5 would be open.