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Modified AC Light Source for Constant Output

IP.com Disclosure Number: IPCOM000046406D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Burke, AJ: AUTHOR

Abstract

This synchronization circuit effectively modifies an AC light source to provide a constant output to an optical signal. The circuit synchronizes the data sampling rate of an optical processing tool to the AC light. Specifically, the data sampling rate is synchronized with the peak intensity of the AC light source. AC variations of the source are eliminated from the optical information presented to a controlling computer for a tool, such as the automatic aligner of a wafer exposure tool.

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Modified AC Light Source for Constant Output

This synchronization circuit effectively modifies an AC light source to provide a constant output to an optical signal. The circuit synchronizes the data sampling rate of an optical processing tool to the AC light. Specifically, the data sampling rate is synchronized with the peak intensity of the AC light source. AC variations of the source are eliminated from the optical information presented to a controlling computer for a tool, such as the automatic aligner of a wafer exposure tool.

Fig. 1 shows an example of an optical signal 10 containing AC light source variations. Fig. 2 shows the same signal obtained by a controlling computer (not shown) for the tool. The signal is received through an analog-to-digital converter (not shown) which is synchronized with the peaks of an AC light source.

Fig. 3 shows the synchronization circuit which combines both a peak detector circuit 12 and a level detector circuit 14. The peak circuit 12 tracks the maximum intensity of a light source 16 while the circuit 14 automatically switches the mode of the peak module. A photodiode 18 converts an optical signal from source 16 into an electronic signal 20 (Fig. 4A) which can be amplified at node A. When the signal 20 is below 5 volts, the circuit 14 sets the peak detect circuit in a reset mode. As the signal at node A crosses above the 5 volts, the circuit 14 switches the circuit 12 into a peak tracking mode, as shown in Fig. 4B for node...