20 / 30
172
CAPITOLO 6
■
Ampli!catori
R
S
V
S
R
in
R
L
V
L
R
u
V
in
v
u
= Gv
in
Fig. 6.1
Amplicatore di tensione.
$QDOL]]LDPR RUD LO FDVR LQ FXL VL GHEED OHJJHUH LO VHJQDOH GL FRUUHQWH GD XQ JHQHUDWRUH
IRU]DQWH DPSOL¿FDUOR H TXLQGL IRUQLUOR DQFRUD FRPH VHJQDOH GL FRUUHQWH DO FDULFR )LJ
6LD
I
s
LO JHQHUDWRUH GL FRUUHQWH FRQ UHVLVWHQ]D SDUDOOHOR GL VRUJHQWH SDUL DG
R
s
OD FRUUHQWH q
I
I
R
R R
in
s
s
s
in
= ⋅
+
TXLQGL SHU PDVVLPL]]DUOD VL GRYUj DYHUH
R
in
<<
R
s
&LRq OD UHVLVWHQ]D GL LQJUHVVR GL XQ DPSOL¿
-
FDWRUH GL FRUUHQWH GHYH HVVHUH SLFFROD ULVSHWWR DOOD UHVLVWHQ]D GHOOD VRUJHQWH GL VHJQDOH ,Q DOWUL
WHUPLQL LO FLUFXLWR GL LQJUHVVR GL XQ DPSOL¿FDWRUH GL FRUUHQWH GHYH HVVHUH XQ RWWLPR ³OHWWRUH
GL FRUUHQWH´ DO OLPLWH XQ FRUWRFLUFXLWR $OO¶XVFLWD LQYHFH DI¿QFKp VLD PDVVLPD OD IUD]LRQH GL
FRUUHQWH UHDOPHQWH IRUQLWD DO FDULFR
R
L
ELVRJQD DYHUH
R
u
>>
R
L
FLRq FKH LO VHJQDOH DPSOL¿FDWR
YHQJD HURJDWR DO FDULFR FRQ XQ¶DOWD UHVLVWHQ]D
(VLVWRQR DQFKH DPSOL¿FDWRUL D
trans-resistenza,
FKH OHJJRQR XQD FRUUHQWH HG HURJDQR VXO
FDULFR XQD WHQVLRQH DG HVVD SURSRU]LRQDOH )LJ
7DOL DPSOL¿FDWRUL GHYRQR SUHVHQWDUH
EDVVH UHVLVWHQ]H GL LQJUHVVR H GL XVFLWD 9LFHYHUVD XQ DPSOL¿FDWRUH D
trans-conduttanza
)LJ
OHJJH XQD WHQVLRQH LQ LQJUHVVR HG HURJD XQD FRUUHQWH DG HVVD SURSRU]LRQDOH /H UHVLVWHQ]H
GL LQJUHVVR H GL XVFLWD GHYRQR HVVHUH HQWUDPEH DOWH
R
S
I
S
R
in
i
in
R
u
i
u
=Gi
in
R
L
i
L
v
L
Fig. 6.2
Amplicatore di corrente.
R
S
i
S
R
IN
R
U
i
in
v
u
=Gi
in
R
L
v
L
Fig. 6.3
Amplicatore a trans-resistenza.