Abstract: Circuits and methods for detecting the presence of a powered device in a powered network connection and removing power from the powered network connection when no powered device is present are disclosed. The circuits and methods involve applying a time-varying voltage signal into an analog amplifier circuit that converts the voltage into a current indicative of the impedance of the connection. The analog amplifier circuit may be implemented with a dual-output trans-conductance amplifier that provides a digital voltage to indicate the removal of the powered device from the powered network connection.

Abstract: A current mirror circuit 10 is coupled to a first and a second photodetector 18 and 20 and differentially couples together the two photodetectors to an amplifier 12 such that a resulting differential output current is independent of the intrinsic responsivity difference between the two photodetectors. The circuit includes a first transistor 14 having an input terminal coupled to an output terminal of the first photodetector and a second transistor 16 having an input terminal coupled to an output terminal of the second photodetector. A capacitance 22 is coupled between a control terminal of the first transistor and a control terminal of the second transistor, the control terminal of the first transistor further being coupled to the input terminal of the first transistor. A first switch 24 is coupled between the control terminal of the second transistor and the input terminal of the second transistor.

Abstract: A read-out amplifier (200) for a photovoltaic detector (201) employs an integrating amplifier (203) with capacitor feedback (230 ) during a self-calibrating active load (205, 240) to minimize debiasing of the photovoltaic detector during its operation. The self-calibrating active load reduces the effect of noise and threshold nonuniformities of the semiconductor devices (202, 203, 204, 205) used in the read-out amplifier circuitry.