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6.6

Ampli!catore operazionale (OpAmp)

181

V

p

V

p

V

n

V

o

V

o

V

n

V

d

R

d

R

o

Av

d

+

_

+

_

Fig. 6.9

L’OpAmp: schema circuitale (sinistra) e circuito equivalente (destra).

1H FRQVHJXH FKH VROR SHU IUHTXHQ]H EDVVH GRYH _

G

loop

j

Ȧ

_!! LO WUDVIHULPHQWR GHO VLVWH

-

PD GLSHQGH GDL VROL HOHPHQWL FKH LQWHUYHQJRQR QHO EORFFR GL UHD]LRQH H TXLQGL QRQ q LQÀXHQ

-

]DWR GDOOH WROOHUDQ]H H GDJOL HOHPHQWL DWWLYL SUHVHQWL QHO EORFFR GL DQGDWD $OO¶DXPHQWDUH GHOOD

IUHTXHQ]D LQYHFH LO WUDVIHULPHQWR WRUQD DG HVVHUH LQÀXHQ]DWR GDO EORFFR GL DQGDWD

6.6 Amplicatore operazionale (OpAmp)

/¶DPSOL¿FDWRUH RSHUD]LRQDOH 2SHUDWLRQDO $PSOL¿HU q XQ DPSOL¿FDWRUH GLIIHUHQ]LDOH GL WHQ

-

VLRQH FRQ JXDGDJQR HOHYDWLVVLPR FKH YLHQH DPSLDPHQWH XWLOL]]DWR FRPH EORFFR DPSOL¿FDQWH

QHL FLUFXLWL UHWURD]LRQDWL 3HU WDOL FLUFXLWL q PROWR LPSRUWDQWH DYHUH OR VWDGLR DPSOL¿FDQWH FRQ

XQ DOWLVVLPR JXDGDJQR SHU RWWHQHUH XQ HOHYDWR JXDGDJQR G¶DQHOOR 1HOOD SURJHWWD]LRQH GHL

FLUFXLWL DQDORJLFL O¶2S$PS q PROWR XWLOL]]DWR VLD SHU OH VXH FDUDWWHULVWLFKH TXDVL LGHDOL VLD

SHUFKp SHUPHWWH GL DPSOL¿FDUH FRQWUROODUH H JHQHUDUH IRUPH G¶RQGD DYHQWL IUHTXHQ]H FKH

VSD]LDQR GDOOD FRQWLQXD ¿QR D PROWL 0+] /¶2S$PS FRQVHQWH LQROWUH GL VYLOXSSDUH LQ PRGR

VHPSOLFH OH VHJXHQWL IXQ]LRQL DOJHEULFKH VRPPD GLIIHUHQ]D PROWLSOLFD]LRQH GLYLVLRQH LQ

-

WHJUD]LRQH H GHULYD]LRQH

,QWHUQDPHQWH O¶DPSOL¿FDWRUH RSHUD]LRQDOH q FRPSRVWR GD XQD VHULH GL DPSOL¿FDWRUL D WUDQ

-

VLVWRU PHQWUH OD VXD UDSSUHVHQWD]LRQH FLUFXLWDOH q PRVWUDWD LQ )LJ *OL LQJUHVVL LGHQ

-

WL¿FDWL GDL VLPEROL

+

e

VL FKLDPDQR ULVSHWWLYDPHQWH LQJUHVVR QRQ LQYHUWHQWH HG LQJUHVVR

LQYHUWHQWH /H UHODWLYH WHQVLRQL PLVXUDWH ULVSHWWR D PDVVD VL LQGLFDQR ULVSHWWLYDPHQWH FRQ

V

p

e

V

n

PHQWUH OD WHQVLRQH G¶XVFLWD FRQ

V

o

.

3RQHQGR XQD WHQVLRQH GLYHUVD DL PRUVHWWL G¶LQJUHVVR

V

p

e

V

n

VL RWWLHQH XQ¶XVFLWD

V

o

legata

DOOD WHQVLRQH GLIIHUHQ]LDOH

V

d

=

V

p

V

n

WUDPLWH LO JXDGDJQR GLIIHUHQ]LDOH

A

d

$SSOLFDQGR OD

VWHVVD WHQVLRQH DL GXH PRUVHWWL O¶XVFLWD q OHJDWD DOOD WHQVLRQH GL PRGR FRPXQH

V

cm

V

p

+

V

n

WUDPLWH LO JXDGDJQR GL PRGR FRPXQH

A

cm

.

9ROHQGR VLQWHWL]]DUH LO WXWWR LQ XQD VLQJROD IRUPXOD VL SXz VFULYHUH

2

V A V V A

V V

ˆ

O d

p

n

cm

p

n

(

)

= ⋅

− + ⋅

+ 

Eq. 6.13

,O UDSSRUWR HVSUHVVR LQ G% WUD

A

d

e

A

cm

q LO &055 JLj GH¿QLWR FRPH

20

10

CMRR A A

A

A

ˆ

log

d cm dB

d

cm

(

)

=

= ⋅





Eq. 6.14