amplifiers. Bandpass amplifiers are also commonly referred to as tuned amplifiers. These ...

47 Pages·2010·1.58 MB·English

7-1 Intreduetion

In this chapter we consider the analysis and design of bandpass
anmplitiers. Baudpust amplitiers are also commonly roferred fos tuned
amplifiers. These amprifers fd miny applicatices m teiecomonaica
‘dons, such 2s in radio, nular, and televiston receivers. 20 mauve 2 fur
To ilusteate the requirements on the Bandpass umplifier, sanauder the
block diagram ef s simpie communicstion system, as shown int fg 7

‘he fput signalisa massage wave f(0} which can be expressed in terms
caf its Fourier seris@or Fourier inte2ral and i assumed lo consiat of a

ous

Fig 7-4 Simple atsplauale-meduiatod sytem
F922 cw) Mesage sis) Aupliote module

Fo a ad chi Ac

Analyse and Delgo Examples of Bendpaee fpr

‘hand offow frequencies inthe viinty of de frequency. The modulator
‘wandlateathishand of frequencies loa nes bond frequencies entered
around the carrie requeney 0 without dstarbig the relative postion
of various hegucncy compontets ofthe signe. For cxarple for sn
amplitade-moduloted (AM) signal

el = [= ill oosnt oy

here Ws the amplitude ofthe earrier signal. The magnitude of Fit)
js always adjusted lobe less than ¥,bence he envelope ofthe modul-
ted signal never drops ty atu. The message signal and the modulied
‘wateform aze shown in fg 7-2. To hasta, consider 8 special case
of a single fequancy, is, e,ftl= Vycustirg + In this ease
from (1)

Heh ~ [he = Bac

= HEU + meoslagt + Oqileos ind

4 8 Teosent

a

where mt — 1, elle the modbfatiom index and is always tess tha
tail, and or > a. We may tewriee 12), using the tigonametnc
Fdemity of the preduct of wo cosines, a6

sem Yomayt 4 onli aw

eos[lo, ai Od

[Noe that {7-3} consists of thtse frequency component, the cucier
Frequency and two sule wave frequencies, Ioeated symmetrically on
titer side of the earree frequency

Tn the penoral ease there are many signul Foquenty components
radhence many pairs al side wave, These ate elle ths mpper and he
Tower sideband ofthe AM wave. Thecurie Irequeacy is sal mvc
higher than the highest troguency in the meduluting spnal The ao.
modulo in fig 7-1 convert the signal informatiun back Ls ig
Trnen The porprng ofthe bandpas® rapier isto perform « SHering
funtion in addition 10 feque}-seletive amplification. The apni
hnde and phase chaructoniaies 0 the idea! bandpass amplior are
shown in fg 7-2. The corcesponchng chantctensis or the sesizale
tuned amples are shown in fig 7-38, The bandwith yp — 4 2,
ina narrow-band amplifiers much smaller than the exter radian fe
‘Guenes ry Inother words foranarcow-band stain, gp © 0444,
28 Singo-Tuned ftarstga 01

and fr chi cae considerable srmpfiention is achieved fu the desine

ss dmonsruted i ster sections of Ue chapter

"The efactenes ofthe Neorg is racasured by dks "skut™ ofthe

smagaivudsrorpanse in fig 7-3b. Quenrcatessly, this measuce ie abven

by seterity,sthich Is given aioe By — 60-38 ty — GE Feeney

Eivar WB Co 4 Ub ratio eas shown inHg?

“The design wf a hunlpass ampere shall soon 28. hus surne

aspects rom on to thore of loxpass anette design, especially ic

be ncon-hund etse, There are certain falures of the design in
handpass arpliee “hat are quite diferent from those of Tepes
Smplifers The ehie? peaklom in banipnes amplce desi is the
Pskiblity f oneitation, doe the reeive lad athe ‘alerts red
feck ofthedevise.e ge € of C8 tansabrrorthe Caf cama
source FET Sine: €;playsan portant undesicablerleya the desea
alexis the penta insablity of ths dove (se Section 2-H. the
Uniareal medsl vannct. ig genes he used Tor an inductive loa
Fer narrowband cone anplies he transistor "wo-porl param:
tes are mewsured at the velar frequency aed then the ogy 6
Tnsed on the approximation thal thewe partneters do not change 28
the pussbund af the amplier, Since the passband extends at most co
1: per eent ofthe cones faquones. fn a narcoR-band sual. his
gpresimatv is wally valid. For a widesnd design, sismatching
tachnigue rst bees astra in Sections 7-12 and 7

| 72 Single-runsa interstage

Ore of the simplest and most sommoaly aval bumlptss plier
Imeestgon the so-called sngle-tuned amper. ‘Ike sre singh
used inate shown in Big 7. This eeeut is u sage oom Fg 7-4. Siogletuna she
scout and provale 4 yood teh’ fr incredusing the analsis and

Ussgn of tuned amplifiers, The wollae-qaiaTunstian ofthe eit is

seven by

where Cy i the coral Imossage capictance und G — Lit. Bypation
(7s alto sometimes refered to a5 the resonitor express,
{HAealpsin and Daslgn Examen of Ewadpats Amotifere
“The magnitude of he pun funcion is

Major = Be

CO vieenar tune cep OF

"The magnitude is maximum at the Frequency where the denominator
oF (7-5) 1s inion. This requenes is commonly calla he cener ot
‘Ge resonant fayuency and it denoted by 0. Hone

cc
[Note dha ty the gin is

Ad oy

“The frequencies st which the gain function is down by $28 fou the
cents fequeney alsa called halFpower frequencies) ac determined
from (Pon (7-7) that i

(ESL EP acca tioe oar

‘he twu sulaions of 8) are

4 eT ORE 935

+a oC? 1754)

as
bras

[Note that ty, the pas sift oF 4, in-2270, wile at the sates
phase shifie anc 445% rxpucsvcy, The — 5-48 bandiidth of the
‘Grout ie ceded asthe ifirenoe between the 2a bandedge fe
ueveiey namely

as

Ato, Cum (7-994 17-10) me can be for Lene the hand
7-2 Sinafe-Tommd fntortogs

‘ioquencis. The ests

ot oft we deal with wires ined am pies, where gy
dey. Hor such ces, roma 2) amd 7-10, ae able

The pola plot of J-tifor a nurtowband luned amplticeiaskown
inf

‘Avesta term in taned amplifiers s the sow Q ofthe ee
The Q ofa single-rmsed ciult w dtioed as

From 7-8) (7-194 al (2-19 wehare

«

ont, ~

oly
Nate that a narrow-band case feyyg «© e) mane a high Q fhe
@> by.

Subecituuon of 7-6) and (7-10) gto (7-41 elds a weft form forthe
single-tuned ample

AI Et nas |e! Oise
cin normalized for
“ A 3
Aled Oi, + ©
whet 5, = eng
‘Note that (al can slay bs cepuesed as
= =k
AU = CE RC, - Rajat ay

TTL aR Heety “wid

5 78 Howat ptf td ne

a ae
Analyte and Dostan Exeopies of Bandpass Amlitirs H

Substation of (7-7 and (7-14) nto

64) pels

Aso) a
Avvo "OA = ia

(66)

A plot ofthe magnitude and phine of (166) for 1Wo volees of @ is
shown in 6g 7-5, We may expres the expos in the passband of the +
sarcon-hand snaps y ling ay — 11 B with A

Heree (7-166) zedees to

'
V+ 200

Ait

Ay rise,

‘The reponse charostevistg of (7-160) estentilly the samme 36 in
fig 76. The cove ut i788 commaorly called tae rerauanre eure

‘The paunbandiwith peaduet (GPL uf ths da ye tuned sage fen
Jane Iii given By

GRP = LA.

Wie shall lustre We above expressions hy two examples ia Une
Inowing
CCorsider the resistve-loaded single-umed :ranscioe stage shown,
cexcsve uf bissig creuites. ing 77a. For simply. we assume
tar f= O and het Ue vl loss and she peruse apzicance of he
anductos ar inched in Ry 2rd. respetoey tie wil becscsned
Ass.

Siacethe loa ie osstive we cu ase-ka simpli unatral mel
wl incor le Mille efit 6 shine fg 7-7, Note chat
Irom 3-10 Cy = th + R,Coe/ Foy. ae einen nxleivn where all
the capacitanas and conductances are combed.

‘os a Spin cv

i “The current gan function uf he amples

mak
FRE

|

‘he above aquation is of idantial form to (7-4, henge the midhand
sain and the 1 dR bandwith are given by

L
: Adin) = Rk ora ™ Re
{anatyal and Devten Exams of Bandeas Amtiare

To Mustiate the abose numerically. consider a tansiscul with the
fatlowing pavaeeters:

fn 2OMHe hy
7, = 209 6

00
pF

‘The other circuit element valuer ure

K.-W Am Lt yt —C = 2000p

som ig 17e, we Hod

Re RR) 2IIAD = Lh
Cy 0, +E, = 2000 4 90) pF = 208» 107%

The resomant Frequency, hum is

= Limite

“The midband guin, the Mls bindsih, snd the @ ofthe circuit are

Atal 9h

kite, = AS

The analsis and desig of one single-tned stage cropoyiag an FET

‘3 Sacuim fhe aze quite x ilar the a30ve, except that the D4

‘RUC cacuit i formed a he ontputciteut for these devices. .
he design ofa singh ssge “or i pesied veer Frequency,

fo. and a Bandoidiby fy, fotos cirelly thom TF) and (740,

Respective.

‘Consider a simple design example. using an FIT tin Be Ta ich
the Tulinsing parameters

Bef IO ah Cy APF Gy 2 Gy, 2 SPE Ig = 20K
7.2 Sinale Tuned Intoatego

[Nove thatthe FET hs tke shunt ten ere at te vp, since the
dleieg ie excited by a voltage source,

The design specications forthe stags, shawn exclusive of busing
cieeiry in Be 7-8, are

y= BSUS Ne, stgyy = 2410"

and a endhan voltage gain jg) = 10.
eon the gl eairemats, we tee

Adjosi = nd leg — i Ry 29K

From the hantwideh specifestion

on = deta tla

Sibsutin of the wah nthe whee and solving for Cg
(a=
“ih
Frome resuant foquency eguvement we ave
i it L

Tee Gp ERTS aston

ye 8 00064

39TH

to ths eg, the erseast values are practical and the inital cig is
scope

(Ofeo a the design of tuned amples. the vafbe ofthe incucter
sya be practic, Tn other words, 1Be enducor may not have &
high 2, and the use of teansformers may Be patesary. For exampl
consider the inclusion of the udietor co Tiss, a SHOMD BS 2 Svis
rena, 7, in fig 7a. For coneenigfoe, the circ «nay be teanke
orem nia paral cizcut, ax shown fig 7.9, where Ie eulealent
paclll rosie, 7, [8 eadlly determined from

Yue) oa

or a bah @ cou

1 ft Ci ing he cs Egan!
‘motel fora eo
408 Trays nd Dengn Grannies of Banyane AroNtiors

and (7-1taycan be writen appreninately 25

P= la, = ate, e183)

at

Thes.ifthe oil Q isnot high enough, th value afr, may beotthe same
onder of magnitude as in fig eof fg 7-AD. ate the eieait Q wil
he Tawered (Le. gq il he increased, Ths the eect ofthe en oss,
rca, cane, gonaeal be ignored

7-3. tmpadones Transtormet
Coupting

fond Transformer

a ee ta una ced te

pene 0993;

gel fo the sntoneyosfovene,nogletag. Abe lye «akon a
4. 7-40b, sre 2a Ihe util Mawctcivg inducing chaeacenced
‘oF she prin sd and ny the He ratio. Note aloo th he he
Coansfunines is ue the vallage pain is elusd by a faces of Le 0)
The cureetyaiz my insteased by Fator of ema slealowr same,
[For ths reason, ane naually considers powr guin in tuned umpiiers,
‘wisch would be unaffected na Josie Iealoringt. Oem dou

Topped inductance ar a combuautioy of capped primary inlersiage