An improved preamplifier circuit has been designed for processing the output of an avalanche photodiode (APD) that is used in a high-resolution laser ranging system to detect laser pulses returning from a target. The improved circuit stands in contrast to prior such circuits in which the APD output current pulses are made to pass, variously, through wide-band or narrow-band load networks before preamplification. A major disadvantage of the prior wide-band load networks is that they are highly susceptible to noise, which degrades timing resolution. A major disadvantage of the prior narrow-band load networks is that they make it difficult to sample the amplitudes of the narrow laser pulses ordinarily used in ranging.
In the improved circuit, a load resistor is connected to the APD output and its value is chosen so that the time constant defined by this resistance and the APD capacitance is large, relative to the duration of a laser pulse. The APD capacitance becomes initially charged by the pulse of current generated by a return laser pulse, so that the rise time of the load-network output is comparable to the duration of the return pulse. Thus, the load-network output is characterized by a fast-rising leading edge, which is necessary for accurate pulse timing.
On the other hand, the resistance capacitance combination constitutes a low-pass filter, which helps to suppress noise. The long time constant causes the load-network output pulse to have a long shallow-sloping trailing edge, which makes it easy to sample the amplitude of the return pulse. The output of the load network is fed to a low-noise, wide-band amplifier. The amplifier must be a wideband one in order to preserve the sharp pulse rise for timing. The suppression of noise and the use of a low-noise amplifier enable the ranging system to detect relatively weak return pulses.
This work was done by Alexander Abramovici and Jacob Chapsky of Caltech for NASA's Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-30598
This Brief includes a Technical Support Package (TSP).
Photodiode Preamplifier for Laser Ranging With Weak Signals
(reference NPO-30598) is currently available for download from the TSP library.
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Overview
The document outlines the NASA Tech Brief NPO-30598, which presents an innovative technology known as the Avalanche Photodiode Preamplifier designed for laser ranging applications, particularly in scenarios involving very low signal levels. This technology is developed by NASA’s Jet Propulsion Laboratory (JPL) and is part of the agency's efforts to advance aerospace-related developments that have potential commercial, scientific, or technological applications.
The Avalanche Photodiode Preamplifier is specifically engineered to enhance the detection of weak signals, which is crucial for laser ranging systems used in various fields, including space exploration, remote sensing, and precision measurement. The ability to accurately measure distances with minimal signal strength is vital for missions that require high precision, such as those involving planetary exploration or satellite positioning.
The document emphasizes the importance of this technology within the framework of NASA's Commercial Technology Program, which aims to disseminate aerospace innovations to broader markets. By making these advancements available, NASA seeks to foster partnerships and collaborations that can lead to further technological developments and applications beyond the aerospace sector.
Additionally, the document includes contact information for the Innovative Technology Assets Management team at JPL, encouraging interested parties to reach out for further assistance or inquiries regarding research and technology in this area. The notice also clarifies that the information provided is subject to U.S. export regulations and may contain proprietary information.
Overall, the document serves as a technical support package that not only highlights the capabilities of the Avalanche Photodiode Preamplifier but also positions it as a significant contribution to the field of laser ranging technology. It reflects NASA's commitment to innovation and the transfer of technology for wider use, ultimately aiming to enhance scientific understanding and technological progress in various domains.
