Patent attributes
A bipolar high impedance element comprises a p-n diode made from a compound semiconductor, and circuitry arranged to reverse-bias the diode such that the diode conducts a nearly constant current—thereby enabling the element to be employed as a high impedance element. The diode is preferably the base-emitter junction of a transistor made from a compound semiconductor like InP, such that an on-chip high impedance element is provided for a fabrication process such as that used for HBTs. The element is suitably employed in an active low pass filter design: the element is connected between an input signal and an op amp input, and a feedback capacitor is connected between the op amp's output and input. The resulting filter's time constant varies with the reverse-biased diode's impedance and the capacitance of the feedback capacitor.
