Automatic gain-controlled amplifier for beam profile monitors

NUCLEAR 1N57RUMEN75 AND ME7H0D5 96 0971) 3-8; •

AU70MA71C

6A1N-C0N7R0LLED

N 0 R 7 H - H 0 L L A N D PU8L15H1N6 C0.

AMPL1F1ER F 0 R 8 E A M P R 0 F 1 L E M 0 N 1 7 0 R 5 *

P. R06ER5, D. P077ER and V. RADEKA 8r00khaven Nat10na1 La60rat0ry, Upt0n, N.Y., U.5.A.

Rece1ved 10 May 1971 An amp11f1erf0r 6eam pr0f11e 5canner5 0f the m0v1n9-w1retype ha5 6een deve10ped 1n wh1ch 119ht c0ntr011ed re515t0r5 vary the 9a1n 50 a5 t0 pr0v1de c0n5tant peak amp11tude. 7he peak 0utput 519na1 15 1ndependent 0f the 1ntercepted 6eam current 0ver the ran9e4 x 10-~t04 x 10-~0A.7he rm5 n015e151e55than 8 x 10-12 A, and the r15e t1me at max1mum 9a1n 15 20/~5ec. 7he c0ntr01

100p ma1nta1n5 appr0x1mate1y c0n5tant 9a1n dur1n9 a 51n91e 5canner per10d, yet can chan9e the 9a1n 0ver 5evera1 decade5 1n 0ne 5ec0nd. At any 91ven9a1n the amp11f1erre5p0n5e 1511near. W1th th15 amp11f1er1n 0perat10n, 1t 15n0t nece55aryt0 chan9e the 9a1n manua11y, a5 the 6eam 1nten51ty var1e5 0ver the ran9e 0f 6eam current5 c0mm0n1yenc0untered w1th part1c1e acce1erat0r5.

1.1ntr0duct10n

th15 paper 15 t0 de5cr16e a new type 0f current amp11f1er w1th aut0mat1c 9a1n c0ntr01 ( A 6 C ) that w111 0perate 0ver th15 ran9e wh11e ma1nta1n1n9 a c0n5tant 0utput amp11tude w1th0ut d15t0rt10n 0f the 065erved 6eam pr0f11e. 7he re5p0n5e t1me c0n5tant 0f the aut0mat1c 9a1n c0ntr01 15 fr0m 0.1 t0 0.2 5ec 0ver the wh01e ran9e 0f 1nput current5.

7he 0perat10n 0f m0dern acce1erat0r5 at h19h 6eam current5 0f acce1erated 10n5 re4u1re5 an accurate kn0w1ed9e 0f 60th 6eam pr0f11e and p051t10n at var10u5 cr1t1ca1 p01nt5 0f the acce1erat0r 5y5tem. 1n 0rder t0 065erve the 6eam 1nten51ty at the tar9et wh11e 51mu1tane0u51y 5tudy1n9 1t5 pr0f11e and p051t10n at 0ther 10cat10n5, a 10w duty-cyc1e h19h-5peed 5cann1n9 5y5tem 15 u5ed 6ecau5e 1t d0e5 n0t chan9e apprec1a61y the 1nten51ty 0r character 0f the 6eam at the tar9et. 7he 5peed 0f the 5canner 5h0u1d 6e 5uff1c1ent t0 a110w dynam1c 065ervat10n 0f the tun1n9 c0nd1t10n5 0f the var10u5 6eam tran5p0rt e1ement5, 5uch a5 4uadrup01e5 and 5teer1n9 ma9net5, and 1t5 c0rre5p0nd1n9 d15p1ay dev1ce 5h0u1d 6e re1at1ve1y free 0f f11cker 50 that eye fat19ue 15 m1n1m12ed. An 05c111at1n9-100p 5canner wa5 de5cr16ed 6y We9ner and Fe19en6aum1). 1n th15 5canner a 5ma11 waterc001ed tu6e 15 arran9ed 1n the f0rm 0f a 100p 50 that 60th X and Y 6eam pr0f11e5 are 5canned w1th a 51n91e 5canner. 7he 5canner ha5 an aperture arran9ement w1th a 119ht 50urce and a ph0t0d10de that 9enerate5 f1duc1a1 mark5 0n the d15p1ay c0rre5p0nd1n9 t0 the X and Y p051t10n 0f the ax15 0f the 6eam p1pe. 7he pr061em 1n 065ervat10n 0f the 6eam pr0f11e and p051t10n 15 that the 6eam current may chan9e 6y 5evera1 0rder5 0f ma9n1tude when the acce1erat0r 0perat1n9 c0nd1t10n5 are chan9ed. 1n 0rder t0 acc0mm0date the5e 1ar9e current chan9e5, an 0perat0r w0u1d have t0 5e1ect the 9a1n 0f a current amp11f1er manua11y every t1me a parameter 15 chan9ed that a1ter5 the 6eam current. 7he ran9e 0f current5 1ntercepted 6y the 5canner extend5 0ver 50me 51x 0rder5 0f ma9n1tude, fr0m a60ut 10 -9 t0 10 -3 A. 7he purp05e 0f * w0rk 5upp0rted 6y the u.5. At0m1c Ener9y c0mm15510n.

2. 8a51c c0n51derat10n5

7he 6a51c appr0ach 15 t0 5amp1e the wavef0rm5 c0rre5p0nd1n9 t0 6eam pr0f11e at the1r max1mum and t0 c0ntr01 the 9a1n 0f the current amp11f1er 50 that the wavef0rm amp11tude rema1n5 near1y c0n5tant. 7he re4u1rement5 0n the t1me re5p0n5e, 519na1 ran9e, 6a5e11ne 5ta6111ty and n015e make the 1mp1ementat10n 0f th15 6a51c appr0ach d1ff1cu1t. 7he aut0mat1c 9a1n c0ntr01 5h0u1d re5p0nd 1n a t1me 5h0rt c0mpared t0 the re5p0n5e t1me 0f the human 0perat0r. 7he r15e t1me 0f the current amp11f1er mu5t n0t c0ntr16ute t0 the d15t0rt10n 0f the 6eam pr0f11e. N015e and 6a5e11ne 5h1ft5 5h0u1d 6e 5ma11 c0mpared t0 a 519na1 at the 10wer end 0f the current ran9e. 7he A 6 C re5p0n5e 15 11m1ted 6y the 5amp11n9 fre4uency, ~, wh1ch 15 determ1ned 6y the 5canner 05c111at10n fre4uency, f0. 7he 5canner 1) 05c111at10n fre4uency 15 a60ut 20 H2. 7here are tw0 X pr0f11e and Y pr0f11e 5can5 each per cyc1e. 51nce X and Y pr0f11e5 can 6e d1fferent 1n 5hape and amp11tude, tw0 5amp1e5 0f the pr0f11e amp11tude can 6e u5ed f0r aut0mat1c 9a1n c0ntr01 f0r 0ne per10d 0f the 5canner. 7h15 5et5 an u1t1mate 10wer 11m1t 0n the A 6 C re5p0n5e t1me c0n5tant, appr0x1mate1y determ1ned 6y "r~,,~2/f~ = 1/f0,

w1th f0 = 20 H2, 25 = 50 m5ec.

4

P. R 0 6 E R 5 et a1.

7he 1ar9e dynam1c ran9e re4u1re5 that the tran51mpedance 0f the A 6 C current amp11f1er 5pan the ran9e fr0m 103 t0 a60ut 109 0. F0r m1n1mum 6a5e11ne dr1ft and n015e 1t w0u1d 6e 6e5t 1f th15 ran9e were c0vered 6y the feed6ack re515t0r 0f 0ne 0perat10na1 amp11f1er. 7h15 15 n0t p055161e 6ecau5e 0f 519na1 r15e t1me re4u1rement5. 7he current amp11f1er 5h0u1d n0t c0ntr16ute t0 the d15t0rt10n 0f the 065erved 6eam pr0f11e m0re than the 5canner c0ntr16ute5 due t0 the f1n1te th1ckne55 0f the 5canner w1re. 7he r15e t1me 0f the amp11f1er 5h0u1d 6e e4ua1 t0 0r 1e55 than the t1me the 5canner take5 t0 m0ve 6y 0ne w1re d1ameter. F0r the de5cr16ed 5canner 1) th15 15 a60ut 60p5ec at an 05c111at10n fre4uency 0f 20 H2. 7h15 1mp05e5 an upper 11m1t 0n the va1ue 0f the feed6ack re515tance 6ecau5e 0f unav01da61e para51t1c capac1tance. ,7heref0re, at 1ea5t tw0 5ta9e5 are re4u1red t0 wh1ch aut0mat1c 9a1n c0ntr01 15 app11ed. Lar9e dynam1c ran9e 1eave5 11tt1e ch01ce w1th re9ard t0 the 9a1n c0ntr01 e1ement. L19ht-c0ntr011ed re515t0r5 6a5ed 0n var1at10n 0f c0nduct1v1ty 0f certa1n 5em1c0nduct0r5 w1th 119ht appear t0 6e the m05t 5u1ta61e 9a1n c0ntr01 e1ement5 1n th15 ca5e. A pr1nc1pa1 d15advanta9e 0f 119ht-c0ntr011ed re515t0r5 15 the1r 510w re5p0n5e, wh1ch pre5ent5 add1t10na1 t1me c0n5tant5 1n the c0ntr01 100p and a 11m1tat10n 0n the 0vera11 t1me re5p0n5e. C0nt1nu0u5 aut0mat1c 9a1n c0ntr01 0ver the wh01e ran9e wa5 preferred t0 the d15crete (5w1tched) aut0mat1c 9a1n c0ntr01 6ecau5e we c0nc1uded that the f0rmer w0u1d re5u1t 1n a 51mp1er 501ut10n. 7he c0mp1ete current amp11f1er w1th aut0mat1c 9a1n c0ntr01 15 5h0wn 1n f19. 1. Current 519na1 amp11f1cat10n 15 acc0mp115hed 1n tw0 9a1n-c0ntr011ed 5ta9e5. 7he th1rd 5ta9e 5erve5 a5 a f1xed 9a1n, 5ec0nd-0rder, 10w-pa55 f11ter. An 1nverter 15 u5ed at the 0utput. 1nput can 6e 0f e1ther p01ar1ty c0rre5p0nd1n9 t0 p051t1ve 0r ne9at1ve 10n5 1n the 6eam. 519na15 at the 1nput and the 0utput 0f the 1nverter are m1xed (netw0rk w1th d10de5 D5 and D6) 50 that a ne9at1ve 519na1 arr1ve5 1n 60th ca5e5 at the c0ntr01 c1rcu1t. A peak 5tretcher w1th a c0n5tant d15char9e rate wa5 ch05en a5 a 51mp1e appr0x1mat10n t0 the 2er00rder, 5amp1e-and-h01d c1rcu1t. 7here are tw0 unav01da61e 1a9 e1ement5 1n the 9a1n c0ntr01 100p. 0 n e 15 pre5ented 6y the f1n1te 5amp11n9 fre4uency, and the 0ther 15 the 119ht-c0ntr011ed re515t0r. 7he 119ht-c0ntr011ed re515t0r ha5 a rather c0mp11cated re5p0n5e wh1ch var1e5 0ver the ran9e 0f 119ht and re515t0r va1ue5. 1t5 very 51mp11f1ed 5ma11 519na1 re5p0n5e can 6e repre5ented a5 a 51n91e p01e netw0rk w1th a t1me c0n5tant vary1n9 fr0m 20 t0 50 m5ec

0ver the ran9e 0f re515tance u5ed here. 1f an 1nte9rat0r 15 1nc1uded 1n the 100p, a c105ed 100p re5p0n5e w1th an e4u1va1ent t1me c0n5tant vary1n9 fr0m 0.1 t0 0.2 5ec 0ver the wh01e ran9e can 6e ach1eved. Due t0 a 1ar9e 519na1 dynam1c ran9e, the err0r 519na1 15 5aturated except f0r a very narr0w re910n ar0und e4u1116r1um. 7here are tw0 appr0ache5 t0 a55ure 100p 5ta6111ty 1n 5uch a n0n11near feed6ack 100p. 0 n e 15 t0 reduce the 5ma11 519na1 9a1n near e4u1116r1um, wh11e keep1n9 c0n5tant the max1mum 51ew rate 0f the c0ntr01 var1a61e (1nte9rat0r 0utput). ,[,h15 c0u1d 6e acc0mp115hed 6y a 51mp1e d10de-re515t0r netw0rk 6etween em1tter5 0f "[•5 and -[•6.7he 0ther appr0ach 15 t0 app1y a c0rrect10n pr0p0rt10na1 t0 the rate 0f chan9e 0f the 519na1 1n add1t10n t0 the a6501ute va1ue 0f the err0r. 7h15 4uant1ty 15 n0t ava11a61e 51nce the 0utput 0f the 5tretcher 15 e1ther 2er0 0r 5aturated f0r 1ar9e 519na1 chan9e5. An a1ternat1ve way, app11ed here, 15 t0 5u6tract fr0m the err0r a 519na1 pr0p0rt10na1 t0 the rate 0f chan9e 0f the c0ntr01 var1a61e. 7h15 15 acc0mp115hed 6y the netw0rk Cf, Rr 1n the err0r amp11f1er-1nte9rat0r c1rcu1t, a5 5h0wn 1n f19. 1. 0 n e 0f the5e appr0ache5 15 e55ent1a1 t0 ach1eve the 5ta6111ty and m1n1mum re5p0n5e t1me. W1th0ut 5uch a netw0rk the 5ta6111ty c0u1d 6e ach1eved 0n1y at the expen5e 0f a very much 1ncrea5ed re5p0n5e t1me, 6y reduc1n9 the 9a1n 0f the err0r amp11f1er and the 1nte9rat0r 51ew rate.

3. L19ht-c0ntr011ed re515t0r 7he re515tance 0f 119ht-c0ntr011ed re515t0r5 var1e5 0ver 5evera1 0rder5 0f ma9n1tude w1th 119ht 1nten51ty. 7he current-v01ta9e re1at10n5h1p 0f the re515tance e1ement 15 11near up t0 5evera1 v01t5, 50 that the 519na1 dynam1c ran9e f0r c0n5tant re515tance can 6e 1ar9e. E1ectr0n1c dev1ce5, 11ke 61p01ar tran515t0r5 and f1e1d-effect tran515t0r5, can 6e u5ed a5 9a1n vary1n9 e1ement5 1n ana109 mu1t1p11er c0nf19urat10n5. 7he1r re5p0n5e 15 much fa5ter, 6ut the ran9e 0ver wh1ch the 9a1n can 6e var1ed 15 11m1ted, a5 we11 a5 the 519na1 dynam1c ran9e. W1th the5e dev1ce5 a num6er 0f 5ta9e5 w1th 9a1n c0ntr01 w0u1d have t0 6e u5ed, each w1th a 5ma11 9a1n ran9e. 7he 0utput 519na1 fr0m the f1r5t 5ta9e w0u1d have t0 6e 5ma11 t0 prevent 5aturat10n at 1ar9er 1nput 519na15 when the 9a1n 15 decrea5ed t0 1t5 10we5t va1ue. N015e and dr1ft5 w0u1d then 6e h19h c0mpared t0 the 10we5t va1ue 0f the 519na1. 7he f19ht 50urce 1n c0mmerc1a11y ava11a61e 119htc0ntr011ed re515t0r5 u5ed here 15 a 5ma11 1ncande5cent 1amp. 7he re515tance e1ement 15 a 5em1c0nduct0r (e.9. cadm1um 5e1en1de) p1ate w1th 0hm1c c0ntact5. Re515tance a5 a funct10n 0f 1amp v01ta9e f0r a typ1ca1 f19htc0ntr011ed re515t0r (Hew1ett-Packard 5082-4510) 15

10K

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+12

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LCR 1 LAMP

1

20K

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-12

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-12

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F19. 1. Current amp11f1er5 w1th aut0mat1c 9a1n c0ntr01.

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50K

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10K

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AMPL1F1ER, 6A1N 2 • L0W PA55 F1L7ER

1~ 75K ~51~

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1

V0L7A6E AMPL1F1ER 6A1N 05 70 250

LCR-HEWLE77 PACKARD5082•4510 L16H7 C0N7R0LLED RE51570R PNP 7RAN51570R - 2N3906 NPN 7RAN51570R -2N3904 D10DE5 - 1N629

~1.8K

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CURREN7 AMPL1F1ER 1K~ 70 5MD 7RAN51MPEDANCE

2~.5K

-12

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120K

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1NVER7ER

:51,0.

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1

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6

P. R 0 6 E R 5

5h0wn 1n f19. 2 . 7 h e capac1tance acr055 the re515tance e1ement 15 a60ut 2 pF. 7h15 capac1tance 11m1t5 the max1mum va1ue 0f the re515tance f0r a 91ven amp11f1er re5p0n5e t1me. A55um1n9 the max1mum va1ue 0f the feed6ack netw0rk t1me c0n5tant 0f 10/~5ec, the max1mum va1ue 0f the re515tance 15 5 x 106 ~. 7he m1n1mum va1ue 15 a60ut 103 f2 at a 1amp v01ta9e 0f 10 V. 7he c0up11n9 6etween the c0ntr01 var1a61e (1amp v01ta9e) and the re515tance e1ement 15 very 10w. 7he capac1tance 6etween the 1amp and the re515tance e1ement 15 a60ut 10 -2 pF, and the 1n5u1at10n re515tance 15 9reater than 1012 f2. 7he t1me re5p0n5e 0f the dev1ce 15 4u1te c0mp1ex. 1t c0n515t5 0f tw0 c0mp0nent5, the 1amp f11ament therma1 t1me c0n5tant and the char9e rec0m61nat10n t1me c0n5tant5 1n the re515tance e1ement. 7he 1atter d0m1nate5 at h19her re515tance va1ue5. Dev1ce5 w1th a d0m1nant t1me c0n5tant 0f 1e55 than 50 m5ec 5h0u1d 6e u5ed 1n th15 c1rcu1t. 7he deta115 0f the tran51ent re5p0n5e are n0t part1cu1ar1y 1mp0rtant 51nce the 9a1n c0ntr01 100p re5p0n5e 15 a150 11m1ted 6y the 10w 5amp11n9 fre4uency.

et a1. •kM

==

1M~

•

2

4. Remark5 0n c1rcu1t de519n and adju5tment5

7he 0vera11 tran51mpedance 0f the current amp11f1er 15 2.5 × 10 9 Q at 1t5 max1mUm Va1Ue. 7h15 C0rre5p0nd5 t0 fu11 5ca1e 5en51t1v1ty 0f 4 x 10 -1° A w1th an 0utput amp11tude 0f 1 V. 7he 9a1n 0f a 51n91e current amp11f1er 5ta9e (a55um1n9 a very h19h 1mpedance 50urce) f0r the 10w fre4uency (5er1e5) v01ta9e n015e and dr1ft5 15 un1ty. C0n5e4uent1y, the tran51mpedance 0f the f1r5t 5ta9e 5h0u1d 6e a5 h19h a5 perm1tted 6y the 519na1 r15e t1me re4u1rement5, 50 that the 5u65e4uent v01ta9e 9a1n can 6e 10w. 0perat10na1 amp11f1er5 w1th f1e1d-effect tran515t0r5 are u5ed t0 m1n1m12e the 1nput current. Ph116r1ck 101 1/02 amp11f1er5 w1th 10w v01ta9e dr1ft5 are u5ed 1n the f1r5t and 5ec0nd 5ta9e. 7he 9a1n c0ntr01 15 arran9ed 50 that a5 the 519na1 1ncrea5e5 6y a60ut 2 decade5 fr0m the 10w end 0fthe ran9e the 9a1n decrea5e5 1n the 5ec0nd 5ta9e, wh11e 1t rema1n5 c0n5tant 1n the f1r5t 5ta9e. 7h15 mean5 that the 519na1-t0-n015e (dr1ft) rat10 1mpr0ve5 11near1y w1th the 519na1.7h15 15 ach1eved 6y 5u6tract1n9 an adju5ta61e c0n5tant v01ta9e fr0m the 1amp LCR1. (1f the feed6ack re515t0r 1n the f1r5t 5ta9e were t0 decrea5e, therma1 n015e current fr0m that re515t0r w0u1d 1ncrea5e, and 519na1-t0-n015e rat10 w0u1d 6e 10wer f0r 5ma11 519na15.) 7he adju5tment 15 perf0rmed at a 519na1 0f 10 -9 A 6y ra151n9 the v01ta9e at the 6a5e 0f710 (re515t0r R1) unt11 there 15 a percept161e 1ncrea5e 1n n015e (9enerated 6y the feed6ack LCR 1n the f1r5t 5ta9e). F0r m05t LCR un1t5 6a5e-em1tter v01ta9e 0n 710 wa5 5uff1c1ent and a 5eparate adju5tment wa5 n0t nece55ary. At the h19h end 0f the 519na1 dynam1c ran9e

100

0

1

2

3

1

5

6

7

8

9

10

11

12

LAMP V0L7A6E (V0L75~

F19. 2. Re515tance a5 a funct10n 0f 1amp v01ta9e f0r a 119ht c0ntr011ed re515t0rHP 50824510.

LCR1 5h0u1d 6e at 1t5 m1n1mum va1ue 50 that 5aturat10n 0f the f1r5t 5ta9e 15 prevented. 7h15 15 ach1eved 6y reduc1n9 the 1amp v01ta9e f0r LCR2 at h19h 1amp current5. An adju5tment 15 made u51n9 re515t0r R 2 1n 5er1e5 w1th the 1amp. At a 519na1 1eve1 0f 10 -3 A, the 0utput 0f the f1r5t 5ta9e 15 m1m1m12ed, wh11e the 0utput 0f the wh01e amp11f1er 15 ma1nta1ned at 1 V. A 5ma11er 519na1 dynam1c ran9e re5u1t5 w1th pre5e1ected va1ue5 f0r R1 and R2 and n0 adju5tment5. 7he re515t0r-d10de netw0rk (re515t0r5 10 kf2 and 240 ~, d10de5 D t and D2) 1n the 1nput 5ta9e 5erve5 t0 ma1nta1n aper10d1c re5p0n5e f0r var10u5 519na1 amp11tude5 and 1nput capac1tance5, wh11e keep1n9 the chan9e 0f p0tent1a1 0f the 5canner 10w. 7he channe1 therma1 n015e 0f the f1e1d-effect tran515t0r 1n the 1nput 5ta9e 6ec0me5 d0m1nant at 10w 519na1 1eve15 w1th the feed6ack re515t0r va1ue5 ch05en. 7h15 n015e 50urce can 6e repre5ented a5 an e4u1va1ent 5er1e5 v01ta9e 9enerat0r 1n the 1nput 0f the amp11f1er. 1t5 c0ntr16ut10n 15 determ1ned (a5 15 the v01ta9e 9a1n) 6y the rat10 0f the feed6ack netw0rk 1mpedance t0 the 1nput netw0rk 1mpedance. 51nce the 1nput netw0rk 15

AU70MA71C 6 A 1 N - C 0 N 7 R 0 L L E D AMPL1F1ER

7

0f c0up11n9 w0u1d 1ncrea5e the re5p0n5e t1me (f0r ne9at1ve feed6ack) 0r cau5e 05c111at10n5 (f0r p051t1ve feed6ack). F0r examp1e, ne9at1ve feed6ack v1a a capac1tance 0f 4 x 10-2pF w1th tran5re515tance 0f 2.5 x 10 9 f2, at max1mum 9a1n, w0u1d 1ncrea5e the re5p0n5e t1me c0n5tant t0 100 #5ec.

ma1n1y the capac1tance 0f 1nput c0nnect10n5, 10n9 ca61e5 6etween the 5canner and the amp11f1er w0u1d re5u1t 1n 1ncrea5ed n015e. 7he n015e 5pectrum 0f current amp11f1er5 1ncrea5e5 w1th fre4uency 6ey0nd the cut0ff fre4uency 0f the feed6ack netw0rk a5 the 9a1n f0r 519na1 current decrea5e5.7he n015e 5pectrum eventua11y decrea5e5 a5 the un1ty-9a1n fre4uency 0f the 0perat10na1 amp11f1er 15 appr0ached. M05t 0f the n015e p0wer f0r w1de-6and current amp11f1er5 15 0ut51de the fre4uency re910n 1n wh1ch 519na1 9a1n 15 c0n5tant. 7heref0re, a 1ar9e 1mpr0vement 1n 519na1-t0-n015e rat10 can 6e ach1eved w1th0ut a 519n1f1cant 1ncrea5e 1n 519na1 re5p0n5e t1me 6y p1ac1n9 a 10w-pa55 f11ter after the current amp11f1er. A 5ec0nd 0rder f11ter 15 u5ed here, a5 5h0wn 1n f19. 1. 7he 1nput 5ta9e 5h0u1d 6e 5h1e1ded t0 prevent feed6ack fr0m the 0utput 5ta9e5. Due t0 a h19h tran51mpedance and a 5h0rt re5p0n5e t1me, a 5ma11 de9ree

5. Re5u1t5 A current pu15e 9enerat0r w1th r15e t1me 0f 1e55 than a60ut 10 #5ec 15 re4u1red t0 te5t the aut0mat1c 9a1n c0ntr01 and the 519na1 re5p0n5e. A 51mp1e 9enerat0r 15 5h0wn 1n f19. 3. Current 5w1tch1n9 15 u5ed at h19her current 1eve15, and v01ta9e 5w1tch1n9 thr0u9h an 1RC HF re515t0r (5 Mf2) 15 u5ed at 10wer current 1eve15. 7he 9a1n c0ntr01 re5p0n5e 15 111u5trated 1n f19. 4 f0r var10u5 1nput amp11tude chan9e5. 7he re5p0n5e t1me f0r a 5tep decrea5e 1n 519na1 6y 51x decade5 15 a60ut 2 5ec, and 1t 15 11m1ted 6y the 51ew rate 0f the c0ntr01 33~

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F19. 3. Current pu15e 9enerat0r.

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F19. 5. Current amp11f1er re5p0n5e t0 1nd1v1dua1pu15e5 at max1mum 9a1n. (a) 5tep re5p0n5e w1th 5h0rt t1me c0n5tant. (6) 5tep re5p0n5e w1th 10n9 t1me c0n5tant. H0r12. 5ca1e 20 #5ec/d1v; vert. 5ca1e 150 pA/d1v.

F19. 4. 6a1n c0ntr01 100p re5p0n5e t0 5tep amp11tude chan9e5. (a) Fr0m 1 mA t0 1 nA; h0r12.5ca1e 0.5 5ec/d1v.(6) Fr0m 1 mA t0 100/~A; h0r12. 5ca1e 0.1 5ec/d1v. (c) Fr0m 100 nA t0 10 nA; h0r12.5ca1e 0.1 5ec/d1v. c1rcu1t, f19. 4(a). 7he re5p0n5e at h19her 519na1 1eve15, f19. 4(6), 15 50mewhat 510wer than at 10wer 1eve15, f19. 4(c). 7h15 15 6ecau5e 0f the 5ma11er rate 0f chan9e 0f re515tance w1th 1amp v01ta9e (f19. 2) at 10wer re515tance

va1ue5, wh1ch c0rre5p0nd5 t0 a 10wer 100p 9a1n. F19. 4(c) 5h0w5 the re5p0n5e at a 519na1 1eve1 at wh1ch the per10d1c re5p0n5e 15 m05t pr0n0unced, due t0 h19her 100p 9a1n and a 10n9er re5p0n5e t1me 0f LCR•5. F19. 4(a) 5h0w5 the effect 0f 1nput amp11f1er v01ta9e 0ffet 0n the 6a5e11ne a5 the 9a1n 1ncrea5e5 t0 1t5 max1mum va1ue. F19. 5 5h0w5 5tep re5p0n5e 0f the current amp11f1er and the effect 0f f11ter1n9 0n n015e and 0n the 519na1, F19. 5(a) repre5ent5 the 5h0rte5t re5p0n5e t1me f0r th15 amp11f1er. F19. 5(6) 15 w1th the 10w-pa55 f11ter ch05en 50 a5 t0 make the re5p0n5e t1me 0f the amp11f1er e4ua1 t0 that 0f the 5canner. 7he n015e 1n f19. 5(6) 15 a60ut 40 p A peak-t0-peak. 7he auth0r5 w15h t0 thank H. E. We9ner f0r 5t1mu1at1n9 and 5upp0rt1n9 th15 w0rk.

Reference 1) H. E. we9ner and 1. L. Fe19en6aum, 1EEE 7ran5. Nuc1. 5c1. N5-14, n0.3 (1967) 1099.