22 / 30
174
CAPITOLO 6
■
Ampli!catori
V
d
(
t
)
V
d
(
t
)
V
cm
(
t
)
V
d
(
t
)
V
g
(
t
)
V
u
= G
(
V'
)
V
u
= G
(
V'
)
V
'
V
'
V
u
= G
(
V'– V''
)
V
'
V
''
a)
b)
c)
Fig. 6.5
Schemi di collegamento di un sensore con un amplicatore.
7XWWDYLD SXz HVVHUH XWLOH HG DOFXQH YROWH LQGLVSHQVDELOH FKH LO VHQVRUH VLD VYLQFRODWR
GDOOD PDVVD ,Q TXHVWL FDVL q QHFHVVDULR ULFRUUHUH DG XQ DPSOL¿FDWRUH GL WHQVLRQH FRQ GXH
PRUVHWWL GL LQJUHVVR HG LQ JUDGR GL DPSOL¿FDUH LO VROR VHJQDOH GLIIHUHQ]LDOH SUHVHQWH D TXHVWL
WHUPLQDOL 9
9
9
0
*OL DPSOL¿FDWRUL VSHFL¿FDPHQWH SURJHWWDWL SHU TXHVWH DSSOLFD]LRQL VRQR
GHWWL DPSOL¿FDWRUL GLIIHUHQ]LDOL )LJ
c
6L QRWL FKH SHUPDQH FRPXQTXH XQD GLIIHUHQ]D GL
SRWHQ]LDOH
V
cm
t
WUD LO VHQVRUH H OD PDVVD GHOO¶DPSOL¿FDWRUH 4XHVWR VHJQDOH q GHWWR VHJQDOH
GL PRGR FRPXQH HG q SDUL DO YDORU PHGLR GHL SRWHQ]LDOL GHL GXH ¿OL GL FROOHJDPHQWR 6H O¶DP
-
SOL¿FDWRUH GLIIHUHQ]LDOH IRVVH LGHDOH TXHVWR VHJQDOH QRQ GRYUHEEH DYHUH DOFXQ HIIHWWR VXO YD
-
ORUH LQ XVFLWD ,O VHJQDOH
V
u
t
VDUHEEH VHPSOLFHPHQWH SURSRU]LRQDOH DO VHJQDOH GLIIHUHQ]LDOH
8Q XOWHULRUH PLJOLRUDPHQWR FKH FRQVHQWH GL ULGXUUH DQFKH LO SLFFROR GLVWXUER GLIIHUHQ]LDOH
DQFRUD SUHVHQWH GRYXWR DOOD VSLUD FKH VL IRUPD WUD L GXH ¿OL FKH FROOHJDQR LO VHQVRUH DOO¶DP
-
SOL¿FDWRUH q RWWHQXWR LQWUHFFLDQGR TXHVWL FRQGXWWRUL FRPH PRVWUDWR LQ )LJ
c
,Q TXHVWR
PRGR VX FLDVFXQ FRQGXWWRUH L YHUVL GHOOH IRU]H HOHWWURPRWULFL LQGRWWH VL DOWHUQDQR SDVVDQGR
GD XQ ORER DO VXFFHVVLYR DQQXOODQGRVL
&RPH WXWWL JOL DPSOL¿FDWRUL GL WHQVLRQH O¶DPSOL¿FDWRUH GLIIHUHQ]LDOH GHYH SUHVHQWDUH WUD L
GXH LQJUHVVL LQGLFDWL FRQ
v
1
e
v
XQ¶DOWD LPSHGHQ]D LGHDOPHQWH LQ¿QLWD PHQWUH O¶XVFLWD GHYH
RIIULUH XQD EDVVD LPSHGHQ]D LGHDOPHQWH QXOOD ,O FLUFXLWR q FDUDWWHUL]]DWR GD XQ JXDGDJQR
GLIIHUHQ]LDOH
G
d
FKH GH¿QLVFH OD VXD FDSDFLWj GL DPSOL¿FDUH LO VHJQDOH GLIIHUHQ]LDOH
V
d
=
V
‘ –
V
“
Eq. 6.3
H GD XQ JXDGDJQR GL PRGR FRPXQH
G
cm
FKH UHQGH LQYHFH FRQWR GHOO¶DPSOL¿FD]LRQH UHVLGXD
LQGHVLGHUDWD GHO VHJQDOH GL PRGR FRPXQH
V
cm
= (
V
' +
V
")/2
Eq. 6.4
/D FRQWHPSRUDQHD SUHVHQ]D GHL GXH WLSL GL VHJQDOH DOO¶LQJUHVVR ID Vu FKH LQ JHQHUDOH LO
WUDVIHULPHQWR GL XQ DPSOL¿FDWRUH GLIIHUHQ]LDOH UHDOH VLD GDWR GD
V
u
=
G
d
·
V
d
+
G
cm
·
V
cm
Eq. 6.5