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Linear Field Photomultiplier Tube Video AGC System

IP.com Disclosure Number: IPCOM000080472D
Original Publication Date: 1973-Dec-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Gorbatenko, GG: AUTHOR

Abstract

An automatic gain control system (AGC) is achieved, by controlling the collection efficiency between the last dynode and the anode of a photomultiplier tube (PMT). All necessary AGC action occurs within the PMT and at voltage levels within the limits of standard transistors.

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Linear Field Photomultiplier Tube Video AGC System

An automatic gain control system (AGC) is achieved, by controlling the collection efficiency between the last dynode and the anode of a photomultiplier tube (PMT). All necessary AGC action occurs within the PMT and at voltage levels within the limits of standard transistors.

Referring to Fig. 1, a ten dynode PMT is shown connected to a conventional power supply 2. A voltage divider 3 provides potentials on dynodes D-1 through D-9, with D-9 connected through a resistor to the positive terminal of the power supply 2 and D-1 connected to the negative terminal. The photocathode 7 is also connected to the negative terminal. Anode 4 is connected to the positive terminal through resistor R1. Dynode D-10 is connected to the output of amplifier
K.

Secondary emission occurs at all dynodes due to the dynode-to-dynode potential of approximately 100 volts. The voltage gradient between anode 4 and dynode D-10 provides a field to bleed off the charge of secondary emitted electrons to anode 4, where the resultant current is converted to an output voltage V5. In general practice this gradient is high, being approximately equal to the other dynode gradients. When this gradient is reduced to about 25 volts, the PMT current starts to drop. At this point, the reduction is near linear and follows the curve as shown in Fig. 2. If the operating point is optimally chosen, a 20:1 dynamic range of the effective PMT gain can be realized.

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