Fast_photo_integrator

Published:2009/7/24 21:02:00 Author:Jessie | From:SeekIC

Figure 5-28 shows a photodiode-amplifier circuit that was specifically designed for situations where the total energy In a light pulse(or pulses)must be measured,The circuit is a very fast integrator, with S1 used as a reset switch, S2,switched simultaneously with S1, compensated the 51 charge-injection error. With the control input(trace A, Fig.5-29)low,and no photocurrent,51 is closed and A1 looks like a grounded follower. Under these conditions, the A1 output(trace C) remains 0 V. When the control input becomes high,A1 becomes an integrator as soon as S1 opens. At this point, the integrator is ready to receive and record a photo pulse. When light falls on the photodiode (trace B triggers a light pulse seen by the photodiode), A1 responds by integrating, and the A1 voltage (after the light event is over) is related to the total energy at the diode during the event. To adjust, cover the photodiode and set the trimmer capacitor for 0-V output from A1 (immediately after the S1/S2 switching function). LINEAR TECHNOLOGY, APPLICATION NOTE 47, P. 42.



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