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6.4

Reazioni negativa e positiva

177

S

in

S

u

S

u

S

f

ε

+

S

in

A

(

s

)

A

(

s

)

F

(

s

)

Fig. 6.6

Dal semplice stadio amplicante (sopra) all’amplicatore reazionato (sotto).

1HO FDVR LQ FXL VLD _

G

loop

_!! DO GHQRPLQDWRUH GHOOD (T VL SXz WUDVFXUDUH H TXLQGL

O¶HVSUHVVLRQH GHO WUDVIHULPHQWR VL VHPSOL¿FD LQ

1

G s

S

S

F s

( )

( )

u

in

= ≅ −

Eq. 6.9

4XHVWD UHOD]LRQH PHWWH LQ HYLGHQ]D FRPH LQ FRQGL]LRQL LGHDOL LO WUDVIHULPHQWR QRQ GLSHQ

-

GD SL GDO EORFFR GL DQGDWD PD VROR GDOOH FDUDWWHULVWLFKH GHO EORFFR GL UHD]LRQH Ê XQ ULVXO

-

WDWR PROWR LPSRUWDQWH LQ TXDQWR LO EORFFR G¶DQGDWD q FRQGL]LRQDWR GD HOHYDWH WROOHUDQ]H GL

FRQVHJXHQ]D EDVWHUj JDUDQWLUH VROR OD WROOHUDQ]D FKH ULVXOWHUj VSLQWD GHO EORFFR GL UHD]LRQH

,QROWUH FRPH VL YHGH GDOOD (T VH

G

loop

q QHJDWLYR H PROWR JUDQGH

G

loop

± DO OLPLWH

ε

VHJQDOH G¶HUURUH WHQGH D ]HUR

6.4 Reazioni negativa e positiva

Ê RSSRUWXQR DSSURIRQGLUH LO VLJQL¿FDWR GHOOD (T LQ IXQ]LRQH GHO VHJQR GHO JXDGDJQR

G¶DQHOOR

G

loop

(VVR KD LQIDWWL XQ¶LPSRUWDQ]D IRQGDPHQWDOH QHO GH¿QLUH OH FDUDWWHULVWLFKH GHO

FLUFXLWR UHD]LRQDWR

6L VXSSRQJD FKH OH GXH IXQ]LRQL GL WUDVIHULPHQWR

A

ed

F

VLDQR GL VHJQR GLVFRUGH DG

esempio

A

! HG

F

'L FRQVHJXHQ]D

G

loop

6H D TXHVWR FLUFXLWR VL DSSOLFD LQ LQJUHVVR

XQ VHJQDOH

S

in

D JUDGLQR SRVLWLYR )LJ D LO EORFFR GL DQGDWD HURJD LQ XVFLWD XQ VHJQDOH

SRVLWLYR /D YDULD]LRQH GHOO¶XVFLWD JHQHUD XQ VHJQDOH GL UHD]LRQH

S

f

FKH JLXQJH DO QRGR VRP

-

PDWRUH FRQ VHJQR RSSRVWR DO VHJQDOH IRU]DQWH H YD D VRWWUDUVL DG HVVR RWWHQHQGR XQ

İ

<

S

in

7DOH UHD]LRQH LQ FXL LO VHJQDOH GL UHD]LRQH WHQGH D ULGXUUH OD IUD]LRQH GHO VHJQDOH GL LQJUHVVR

HIIHWWLYDPHQWH DSSOLFDWD DOOR VWDGLR DPSOL¿FDQWH G¶DQGDWD q FKLDPDWD UHD]LRQH QHJDWLYD /D

UHD]LRQH q QHJDWLYD WXWWH OH YROWH FKH LO SURGRWWR $ā ) q QHJDWLYR RYYHUR TXDQGR LO JXDGDJQR

d’anello

G

loop

q QHJDWLYR QHOO¶HVHPSLR ) q QHJDWLYR HG $ q SRVLWLYR

6L VXSSRQJD LQYHFH FKH L GXH EORFFKL FKH FRVWLWXLVFRQR O¶DQHOOR DEELDQR JXDGDJQL GHOOR

VWHVVR VHJQR )LJ E DG HVHPSLR

A

! HG

F

! WDOL TXLQGL GD GHWHUPLQDUH

G

loop

! ,Q

TXHVWR FDVR LO VHJQDOH ULSRUWDWR DO QRGR GL LQJUHVVR KD OR VWHVVR VHJQR GHO VHJQDOH IRU]DQWH H

YD D VRPPDUVL DG HVVR

İ

>

S

in

8Q VLVWHPD FRQ TXHVWH FDUDWWHULVWLFKH q GHWWR D UHD]LRQH SR

-

VLWLYD /D UHD]LRQH q SRVLWLYD WXWWH OH YROWH FKH LO SURGRWWR $

·

) q SRVLWLYR RYYHUR TXDQGR LO

JXDGDJQR G¶DQHOOR

G

loop

è positivo.