Coded data generation or conversion – Analog to or from digital conversion – Using optical device
Reexamination Certificate
1998-11-02
2001-02-13
Wamsley, Patrick (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Using optical device,
C341S155000
Reexamination Certificate
active
06188342
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to the field of optical signal processing; specifically, the invention relates to the sampling and conversion of analog optical signals into digital form for computer processing of lightwave information.
BACKGROUND OF THE INVENTION
Digital computers far exceed the capabilities and speeds of analog machines for complex mathematical processing. However, a large amount of information that may be processed by digital machines exists in analog form. The analog signals must be converted to digital form before they can be subjected to digital analysis, manipulation and storage.
Electronic conversion of analog signals to digital format is an established technology. But as digital processing capacity and speed has increased with the evolution of better storage and computation hardware, there has been increasing demand for faster analog to digital (A/D) converters to provide higher sampling rates and allow conversion of ever higher frequency analog signals to digital form. Electronic A/D conversion has a frequency limit at this writing of about 6 GHz due to thermal dissipation and fundamental speed limitations of electronic circuits that respond to signal input and create digital output.
High speed electronic A/D conversion requires complex circuits. Typical N-bit flash A/D converters require 2
N
−1 comparator circuits whose outputs must be encoded to produce an N-bit parallel output. Thus, an eight-bit flash converter requires 255 comparators and an eight-bit encoder device to produce an eight-bit parallel output. The electronic encoding of the comparator output is also a major factor in the fundamental speed limitation of electronic converters.
The development of optical analog and data transmission techniques has enabled the expansion of signal bandwidths and operation into higher and higher frequencies for many kinds of systems. These systems must be interfaced with digital computers to take full advantage of the signal processing capabilities of the digital systems. Therefore, it becomes necessary to develop even faster A/D converters to sample the extremely high frequency signals carried on and by lightwaves. Because speed is related to circuit complexity, the simpler the circuit is the faster it may perform. The present invention is directed to providing an A/D converter for lightwave signals, capable of operation into frequencies far above 6 GHz, that is less complex than an electronic A/D converter on a per bit of output basis.
SUMMARY OF THE INVENTION
The present invention is a flash photonic A/D converter comprising an array of photodetectors and high-speed transistors. In the presently preferred embodiment, the photodetector array comprises velocity-matched distributed photodetectors (VMDP). Velocity-matched, distributed photodetectors are optical waveguides on which have been fabricated a number of photodetectors that are interconnected by an electrical coplanar waveguide. An array of these devices is used to detect the amplitude of an optical signal. The output of the array is coupled to a network of high-speed transistors configured as an array of binary switching circuits. One such switching circuit is provided for each waveguide in the photodetector array.
The optical signal is divided among a plurality of parallel velocity-matched distributed photodetector channels. In the presently preferred embodiment, each photodetector channel has a different sensitivity to the incident optical signal. This difference in sensitivity is achieved by varying the number of photodetectors integrated along the optical channel waveguide. The channel with the least sensitivity (that is, the fewest number of photodetectors) determines the most significant bit in the quantization of the lightwave signal. This allows a division of the input analog optical signal whereby a small fraction of the signal is used to determine the most significant bit and greater portions of the input signal are directed to each lesser significant bit. The least significant bit, which requires the greatest quantization accuracy, receives the greatest portion of the input signal which improves the resolution of the A/D conversion.
The detector current from each waveguide channel is fed to the high-speed binary switching circuit. There is one switching circuit for each channel. The threshold for switching the switching circuit is set to produce a digital “high” output at a certain optical detector current input level. When the detector current is below the threshold, the switching circuit remains in a digital “low” state; when the threshold is exceeded, the switching circuit switches to a “high” condition.
Every switching circuit output (except for the least significant bit) is tied to the input threshold circuit of each subsequent bit of lower significance. When a channel output switching circuit switches to a high condition, an electrical load in the switching network is switched into the threshold circuits of each of the lower-order bits, effectively subtracting the input level of the higher bit from each of the lower order bits.
An analog to digital converter for optical signals that transforms analog lightwave amplitude into digital form can be an important building block in communications, medical, defense and industrial systems. The photonic A/D converter of the present invention enables sampling of lightwave signals at sampling rates well beyond the current 6 GHz fundamental rate limit of electronic A/D components.
REFERENCES:
patent: 4502037 (1985-02-01), Le Parquier et al.
patent: 4712089 (1987-12-01), Verber
patent: 4851840 (1989-07-01), McAulay
patent: 4857931 (1989-08-01), Gulczynski
patent: 4947170 (1990-08-01), Falk
patent: 5010346 (1991-04-01), Hamilton et al.
patent: 5264849 (1993-11-01), Kondoh et al.
patent: 5381147 (1995-01-01), Birkmayer
patent: 5684486 (1997-11-01), Ono et al.
patent: 5850195 (1998-12-01), Berlien, Jr. et al.
Seidel, Gonda, Lavorgna & Monaco
Tracor Aerospace Electronic Systems, Inc.
Wamsley Patrick
LandOfFree
Photonic A/D converter using parallel synchronous... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photonic A/D converter using parallel synchronous..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photonic A/D converter using parallel synchronous... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2582009