High-speed adjustable multilevel light modulation
First Claim
1. A method for representing a digital input word as a multilevel modulated output signal having one of n levels, the method comprising the steps of:
- encoding the digital input word into a code having at least one bit;
switching a plurality of output sources, each output source corresponding to at least one bit of the code;
independently adjusting each of the output sources; and
adding the output sources to generate the multilevel modulated output signal.
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Abstract
A multi-level signal is produced from an input signal using a multilevel modulation technique. The input signal is encoded with a desired level code and thermometer decoded to a latch. The latch synchronizes the decoder outputs so that identical current sources can be synchronously activated and deactivated for high-fidelity signal generation around the transition point in time. The current sources are identical circuits with adjustable current settings. The adjustable current sources can be of fixed values as determined by simple electronic circuits (e.g., a resistor circuit) or be adjusted by low-speed high-resolution digital-to-analog converters. These adjustable current settings allow for the current step between levels to be adjusted as required for linearization or as desired for other system considerations. The outputs of the adjustable current sources can be added together to form a multilevel modulated output, whereby each level in the modulated signal is independently adjustable.
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Citations
36 Claims
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1. A method for representing a digital input word as a multilevel modulated output signal having one of n levels, the method comprising the steps of:
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encoding the digital input word into a code having at least one bit;
switching a plurality of output sources, each output source corresponding to at least one bit of the code;
independently adjusting each of the output sources; and
adding the output sources to generate the multilevel modulated output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A multilevel modulator for transmitting an output signal representing a digital input word having n bits over an optical fiber communication system, comprising:
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an encoder circuit for associating the digital input word with a multilevel modulated output code;
at least one independently adjustable current source for representing each bit of the output code as a current level; and
a current adder for combining the current levels of the at least one independently adjustable current source to generate the output signal. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21)
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22. A transmitter for use in an optical fiber communications system, comprising:
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a multilevel modulation circuit operative to encode an input word into a multilevel modulated output code, the multilevel modulation circuit having a plurality of independently adjustable current sources, each current source corresponding to at least one bit of the output code, wherein the output of the current sources are added to generate the output signal; and
an optical source for transmitting the output signal over a link of the optical fiber communications system. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29)
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30. A method for representing a digital input word as a multilevel modulated output signal having one of a plurality of output levels, the method comprising the steps of:
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receiving an input word;
encoding the input word into a code corresponding to one of the plurality of output levels, the code being operative to control a plurality of associated signal sources;
generating a source output for each signal source;
independently adjusting at least one of the source outputs; and
combining the source outputs to generate the multilevel modulated output signal. - View Dependent Claims (31, 32, 33, 34, 35, 36)
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Specification