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Direct coupled amplifiers using field effect transistors

Technical Report:

Abstract

The concept of the uni-polar field effect transistor (P.E.T.) was known before the invention of the bi-polar transistor but it is only recently that they have been made commercially. Being produced as yet only in small quantities, their price imposes a restriction on use to circuits where their peculiar properties can be exploited to the full. One such application is described here where the combination of low voltage drift and relatively low input leakage current are necessarily used together. One of the instruments used to control nuclear reactors has a logarithmic response to the mean output current from a polarised ionisation chamber. The logarithmic signal is then differentiated electrically, the result being displayed on a meter calibrated to show the reactor divergence or doubling time. If displayed in doubling time the scale is calibrated reciprocally. Because of the wide range obtained in the logarithmic section and the limited supply voltage, an output of 1 volt per decade change in ionisation current is used. Differentiating this gives a current of 1.5 x 10{sup -8} A for p.s.D. (20 sec. doubling time) in the differentiating amplifier. To overcome some of the problems of noise due to statistical variations in input current, the  More>>
Authors:
Fowler, E P [1] 
  1. Control and Instrumentation Division, Atomic Energy Establishment, Winfrith, Dorchester, Dorset (United Kingdom)
Publication Date:
Mar 15, 1964
Product Type:
Technical Report
Report Number:
AEEW-M-521
Resource Relation:
Other Information: Country of input: International Atomic Energy Agency (IAEA); 5 figs
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; AMPLIFIERS; CONTROL; DESIGN; ELECTRIC POTENTIAL; ELECTROMETERS; FIELD EFFECT TRANSISTORS; IONIZATION CHAMBERS; JUNCTION TRANSISTORS; LEAKAGE CURRENT; REACTORS; SIGNALS; VALVES
OSTI ID:
20885049
Research Organizations:
United Kingdom Atomic Energy Authority, Reactor Group, Winfrith (United Kingdom)
Country of Origin:
United Kingdom
Language:
English
Other Identifying Numbers:
TRN: GB07A0257050520
Availability:
Available from INIS in electronic form; Also available from H.M. Stationery Office
Submitting Site:
GBN
Size:
18 pages
Announcement Date:
Jul 14, 2007

Technical Report:

Citation Formats

Fowler, E P. Direct coupled amplifiers using field effect transistors. United Kingdom: N. p., 1964. Web.
Fowler, E P. Direct coupled amplifiers using field effect transistors. United Kingdom.
Fowler, E P. 1964. "Direct coupled amplifiers using field effect transistors." United Kingdom.
@misc{etde_20885049,
title = {Direct coupled amplifiers using field effect transistors}
author = {Fowler, E P}
abstractNote = {The concept of the uni-polar field effect transistor (P.E.T.) was known before the invention of the bi-polar transistor but it is only recently that they have been made commercially. Being produced as yet only in small quantities, their price imposes a restriction on use to circuits where their peculiar properties can be exploited to the full. One such application is described here where the combination of low voltage drift and relatively low input leakage current are necessarily used together. One of the instruments used to control nuclear reactors has a logarithmic response to the mean output current from a polarised ionisation chamber. The logarithmic signal is then differentiated electrically, the result being displayed on a meter calibrated to show the reactor divergence or doubling time. If displayed in doubling time the scale is calibrated reciprocally. Because of the wide range obtained in the logarithmic section and the limited supply voltage, an output of 1 volt per decade change in ionisation current is used. Differentiating this gives a current of 1.5 x 10{sup -8} A for p.s.D. (20 sec. doubling time) in the differentiating amplifier. To overcome some of the problems of noise due to statistical variations in input current, the circuit design necessitates a resistive path to ground at the amplifier input of 20 M.ohms. A schematic diagram is shown. 1. It is evident that a zero drift of 1% can be caused by a leakage current of 1.5 x 10{sup -10} A or an offset voltage of 3 mV at the amplifier input. Although the presently used electrometer valve is satisfactory from the point of view of grid current, there have been sudden changes in grid to grid voltage (the valve is a double triode) of up to 10 m.V. It has been found that a pair of F.E.T's. can be used to replace the electrometer valve so long as care is taken in correct balance of the two devices. An investigation has been made into the characteristics of some fourteen devices to see whether those with very different characteristics can still be used or whether selection is necessary or desirable. The results recorded here suggest that either course can be followed or more attractively a combination of the two. It is evident that the characteristics of the P.E.T. are amenable to simple calculation to a far greater extent than is the case with the duo-junction transistor.}
place = {United Kingdom}
year = {1964}
month = {Mar}
}