Abstract: A method for designing a filtering device essentially comprising the steps of determining a desired response of the filtering device at a selected frequency; and selecting a circuit element that exhibits a parasitic effect at the selected frequency, wherein the parasitic effect results in the circuit element having the desired response at the selected frequency. A second method for designing a filtering device, similar to the first, but utilizes a field effect at the selected frequency, instead of a parasitic effect.A frequency converter comprising a notch filter which filters a first frequency and does not filter a second frequency. The notch filter comprises a lumped parameter element and a transmission line, wherein the transmission line is coupled to the lumped parameter element.

Abstract: A biasing and monitoring system for use with a circuit. The system comprises a biasing device, which is coupled to the circuit and which biases a circuit variable; and a monitoring device, which monitors a first indicator variable, and which comprises means for communicating information about the first indicator variable; and a controlling device. The controlling device controls the biasing device, receives information about the first indicator variable, is coupled to the biasing device and to the monitoring device, and comprises means for determining a desired value for the circuit variable.The system can be implemented in an amplifier system comprising a field effect transistor ("FET"). The system biases the gate voltage of the FET so as to minimize the intermodulation products for any given value of temperature. The system uses a look-up table to determine the proper biasing voltage, and desired source current, for any given temperature.