Cunert minor
A ideal (urent minor is a too port cirutt
that acept an input (unent Tn Qna oroduce
utput curent It In:
Also, an ioeal cuent miror will iave zero inbut
resis tane ut Aigh output vslsonce
Bot transis tors care in actve vegicn (s6 the
voltage of Q2 must Ge larger tRan Ve). aiain
* 4! Q anl
Q2.haue
ts gnored , then Qi
tie Same size ,and ite a
ong Q2 have the same
(due to tie Samme V) (urent
6wever, wken nac ae (on
(oger hs oill haue avger sideved,the tansis tor with
larçer Cunent
Iin
Tout
(urrent miTOT input vaistne
follouoing Srmal spal zutaknt
* we use he the
tivuit to (ompute the nput
(urrent mihrar(Is, is cben and low- heeny
mode! i's used
V end
Then,mensure
agpy the
cuynet 19
as
Sn reststane is
Seme times efered to as a ciade onnec ted
tansistor.
in
Vi
Curent mior output vesis tance
* Using the mooel for the toput resis
re vias s(ides leads to a tane fom
nesistne
signal simliftea sma ll
equiulent civart fr the ueral
miryor. (urren t
ut vesislance is given by Yat =Valiao.
Iin
Yat
Sn tats Con-kgura tion, as long as ga te
ferminal is sall - sigmab qramd, the
esis tance looking into the aha in is Vag
fxample
Consider the curent mivrY shn n below
where Tin = fure,
l00AA ano each transi's tor has wh lom
6iven the o-ssum CHos device oatame lers in Table,
fina Yrt or the Current mirrat and the
alue f
9my Alo, estima tthe change in Tat for a loomV
chomgy in the autput vtage what ettage must Ge
main e
tain at the cha in , to ensúe itrema ns in
Iin, JTnut
V2 An Cox (wy)Ioi
= 0.97 mAv
AIout = AV l0omv
Yut 25ke
This is eitimale a taivg bwrfequen Smal
signal Gnear eyuivalen t civait
Ve! = 2I
2osm
Con yn¡n Sour (e
armpli ger
*H Conon ue dsimple cunent mivrs ts 0
be actve loads in a single -stage
amplifer
* 3y using on actve load, a high- impedan te autput
(oad Can Ee vealized o'fat uslng etesivey
largt eustors or alorge ouer suppy
(for example, a look yesis tor (oad twits vothg.
oo MA bias
Cument Leald needa poser supply of a leat oy
* The oonmon Saure (es) toplogy is the mes t ppular
gain stage, espoecialy when high ioput impeaainte
is desitea.
Aetve load
Vat
Vi
Srmall sigml analys f cs: De gain Au
# Asue that all tansists one in actve
vegien,
H&e small signal model af the Cs aplifier with
active Coa d is shown 6elou:
(nate te vesistance Ra is
maoe up poraltel
Depenahag
used, the
on odevice sizes,
(urents and edhnology
typical gain fr a cs ampiher (aula 6e
Ge tween -s
to-lo0
* Av is a bnut one
hil!
half af the tntriaste gatn af
* To maximize he
gain, it is :destvae to
Vey t- foY afxed Gias mininize
tunent, %1s is to mcotaJe w)
-Vat
Snal
Sigmal analygis f cs: in and
Yaut
Sa,ctive load.
oValt
Rs in
Vin
Exomple
Assume Ibias loo WA, all transttors hare l huno
in ciruit and the cene rameers are thase f the
o3sim CMos oress in tble. hat s the gain of the
stage ?
-Aatie
Vet
at
Vin
A LID.
Avz
- 12- v
Coramen chrain amplifer
fho ther goncral use af cunent mirras is to
Supdy the bias (uYent r a (omon- arain or
SurLe fo lower (36) amzhfier.
SF
Sf ampliftes ane (omnnonly used as vdtge bufer
Tpias Veut
Active load.
t fn the Synall sigpal
model, note that the voltage
(otollea Cunent soune tat pdels the
of Mos transis trs ts bodg
oaj efeet
included as theve isim'e
Saril- boag vetage (un ike cs
Soure
Gecome a mmjr Amitaton on theammplsfer), whteh may
Snal sigral galn
nodeling te boalg effect roduesCument saue
a Cument hat
is propartiona! to tie
nakes it equivalert to avoltage
alows to yetsta of a. This
Simplihy the cirutt to te right fond
side.
Ay =Vaut
Vin
Va
Vin
Smal sipnal analysis sf: ro and Yatr
Vout
Yalsa
Actve laad
Transorm to a
resistor when
.(alula ting Vat
Consiaer the sure
all transs tors haive w -2um
lo-2m f o4V anar
Y03vh, and the other aevie poaramt
Parameterters ore teu
of the ol8 Aim (MOsproes, in table. what is the
gain of.he staa asume tat baos
O2m
(oogm le)(oo AA)
UMOs PMos
2 Vest 2
-D4
O.02
2/osv toRv
=o lmAl. |: 6
Ave 24
o3S
o-Sg
4fene,it can be seen that boay
Sune of eror (ausing tie gain effet
af
is the majr
to be (es han o. the sf amplifer
Commn _gat amlifer
* AComnn ga te
amplifer is used as a gam stage
twhen, s1nal input impedane is
is ofen used when the imput desived Aso, tt
Small ipat sipnal is a cunentas
mpedlnte is aêstves.
desires
fom is ouo input tmzcanie, tie Canal-at
ampiher is Similar b a s amplifer as the mput
Siqyal gate sourle tminal and atput
taken form the. Chatn erintnat
ene,nnGoti
Goti anplifes, the
equals -e pockutt af ga end tofal smal signal gtn
at the Oratn tmpecnce
Vecst
ut
Vat
in
1+ Gdsi
1+
Compariscnef the impedance
Vat
VsLrn Vint
Vin
Vaet
R
isVs
G
4f RL is even
Cargr, then ts more than 2
g.
fegueny
5mall signal
rat
Vat
R
Yos
Yut V
SH Re Tas1 =Ydsi Gndr Rso,
en not surprisingy
fxample figue to
gatt amdifer of
Design the Commn appoxima ey
have an input impeoance, af lwrte
CHOs aeie in table
atg ie o-le-Um
WMOS pMos
2701
-o4
Vat
6
Vin
24
Sinec (aL), -(aL we,
ta ke L2 o.2 um
ensure as R Yas!
in 2/gm
en ce , o ensuve n so
gm 2/Croa) = 4omAh.
Sf we take Ve 200my
This
vequives tie curnent mion to proviae a
mirors
Source aegneratea Cunent
Simple cunent mrors presenta Beree
have velatvey syalt cutput impecante. To
incvease this autput mpeaancej a Soure
degneratea current mier Can 6e usea
Tin Tout
aut
Rs
Vgs
Small simal moael to nd
ate
ote tiat in the
smal' stanal model to
Compute Vat, U) the gate votage for koth Q, and
as no Smal sigal tument flous to
ga te, we
neglect the boay eftet
iy 2- gomnRg
Ysn(1t Rs(Gme
9f body effect tncluded
Vgs
Rs
Erample
Consi der the urrent minor shoo whee inzbauy
eoch tansistor has w) : lomo 2m, ond Rzlka
Wing the o.le-m CNos devices,fino f the
Curvent mror- Asume tie boag effet Can be
oppoxima ted loy : oSgmo
Slominally, Tin c), Iat
JTat
Tat Tin, ond ts we?A
fnd tie small simal Rs
poramets for thts turyent
Abo we hae
O-2m
2rka
)
Also no te that the voltage chiop acyoas hR
equals loo uA y1ke: o-1V
There fre, Compare a to the simrgle two
transis tor Curent mirra, the utput impe dante
of Sarte aegenera lear current mìrror has
Tulput impe dane in (reaseo by a fac tor
equal to C14 gmn RJ
bte also that such a fmula toon
oftn 6e apzlhed b mo derately canfliata
Cvui ts to qytekly estmate the inpeakan ee
looking into a noae
