Lockheed Martin Corporation

Parkervision, Inc.

Martin Marietta Corporation

Kevin L Brown

David F Sorrells

Gregory S Rawlins

Michael W Rawlins

Robert James Martin

Peter Falter

Gregory L Milne

Mark West

Kirk Reiff

A multi-band aperture filter for optically coupling to a focal plane array (FPA) of a camera includes a substrate, and a first spectral coating on a first surface of the substrate that passes both a first longer and a second shorter wavelength band. A second spectral coating that passes the longer wavelength band and blocks the shorter wavelength band is on an outer annulus region, but not on an inner region on the first surface or a second surface of the substrate. The second spectral coating provides a larger aperture area for the longer wavelength band as compared to an aperture area for the shorter wavelength band to passively realize different F-numbers for the bands to provide substantially matched beam spot sizes on the detector array for the longer wavelength band and the shorter wavelength band, such as a long-wave infrared (LWIR) band and a mid-wave IR (MWIR) band.

Passive multi-band aperture filters and cameras therefrom

Methods and apparatuses for reducing DC offsets in a communication system are described. In a first aspect, a feedback loop circuit reduces DC offset in a wireless local area network (WLAN) receiver channel. The frequency response of the feedback loop circuit can be variable. In a second aspect, a circuit provides gain control in a WLAN receiver channel. The stored DC offset is subtracted from the receiver channel. First and second automatic gain control (AGC) amplifiers are coupled in respective portions of the receiver channel. In a third aspect, a feedback loop circuit reduces DC offset in a WLAN receiver channel. The feedback loop circuit includes a storage element that samples and stores receiver channel DC offset. The loop is opened, and the DC offset stored in the storage element is subtracted from the receiver channel. Circuits for monitoring DC offset, and for providing control signals for controlling the frequency response of the DC offset reducing circuits are also provided.

Gain control in a communication channel

Method and apparatus for reducing DC offsets in a communication system

A filter module for reducing a DC offset voltage in a radio frequency communication channel is described. A first capacitor is coupled between a first differential input node and a first differential output node. A second capacitor is coupled between a second differential input node and a second differential output node. An active variable resistor is coupled between the first differential output node and the second differential output node. The active variable resistor receives a control signal. The control signal adjusts the value of the active variable resistor, which adjusts the frequency response of the filter module. The rate at which the filter module reduces DC offset voltages is thereby adjusted. The filter module is also adaptable to single-ended applications.

Method and apparatus for DC offset removal in a radio frequency communication channel

A quantum well infrared photodetector includes a direct connection between the charge well and detector that induces a nonlinear dynamic bias. This dynamic bias advantageously corrects for nonuniformity in the conductance of the detector.

Integral charge well for QWIP FPA'S

A multiplexer selects multiple input signals to produce an output in which the distortion associated with switching is minimized. Selection of the multiple input signals is performed within a multiplexing operational amplifier. The operational amplifier includes differential amplifiers that receive the respective input signals at their respective noninverting nodes. The differential amplifiers are connected to a feedback signal at their respective inverting nodes. The input signals are selected for output by turning on selection switches within the operational amplifier, causing the respective differential amplifiers to be selected. This minimizes non-linearities in the output due to capacitive coupling and eliminates unwanted resistive effects without requiring complicated circuitry. The selection switches may include complementary back-to-back MOSFETs, or alternatively, same-channel MOSFETs connected in series to cancel capacitive coupling and switch feedthrough within the multiplexing op-amp.

Method of and apparatus for multiplexing multiple input signals

A quantum well infrared photodetector includes a direct connection between the charge well and detector that induces a nonlinear dynamic bias. This dynamic bias advantageously corrects for nonuniformity in the conductance of the detector. In another feature, the charge well is fabricated on the detector element by adding an extra contact layer and a dielectric layer to a standard quantum well. Very dense focal plane arrays can be produced by making the charge well a part of the infrared detector.

Integral charge well for a QWIP FPA

Apparatus for and method of increasing the effective integration time, and, hence, reducing the noise bandwidth of a photodetector. The current output of the photodetector is converted to a voltage signal in a low pass filter. The low pass filter is preferably implemented as a switched capacitor filter.

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Clermont, FL, United States of America

Kevin L Brown