Level detector for optical receivers
AssigneeTri Quint Semiconductor, Inc.
InventorChris J. Day
Life of this patent
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Abstract
An apparatus and method for detecting an output power level of an optical receiver, in order to hold output signal levels constant over changing input optical levels. A photodetector detects an optical signal, and a current from the photodetector is applied an amplifier. The amplifier may be either a differential trans-impedance amplifier, or a dual trans-impedance amplifier coupled to a differential output amplifier. An output of the amplifier is applied o a signal detector, wherein an output signal of the signal detector is an indication of an output power level of the optical receiver.
Claims10
A circuit comprising:
- a photodetector having an anode and a cathode;
- a differential trans-impedance amplifier having two inputs and two outputs, wherein one input is connected to the photodetector anode, and a second input is connected to the photodetector cathode, the differential trans-impedance amplifier comprising:
- circuitry to electrically isolate the outputs of the trans-impedance amplifier, such that a change in loading conditions on a first output does not alter a signal level on a second output, and wherein an externally induced signal on a first output does not appear on the second output;
- and
- a signal detector connected to one output of the trans-impedance amplifier;
- wherein an output signal of the signal detector is an indication of an output power level of a signal leaving the circuit;
- wherein the circuitry to isolate the trans-impedance amplifier outputs comprises an output stage having a cascode topology to provide electrical isolation between the outputs.
A method of detecting the output power level of an optical receiver, the method comprising:
- detecting an optical signal with a photodetector, the photodetector generating a first current and a second current;
- applying the first current to one input of a differential trans-impedance amplifier, the trans-impedance amplifier having a first output and a second output;
- applying the second current to a second input of an amplifier;
- electrically isolating the first and second outputs of the trans-impedance amplifier with a circuitry, such that a change in loading conditions on a first output does not alter a signal level on a second output, and wherein an externally induced signal on a first output does not appear on the second output;
- and
- applying an output of the amplifier to a signal detector;
- wherein an output signal of the signal detector is an indication of an output power level of the optical receiver;
- wherein the circuitry to isolate the trans-impedance amplifier outputs comprises an output stage having a cascode to topology to provide electrical isolation between the outputs.
Dependencies are inferred from the claim text.