RF Oscillator Design Introduction

8/15/2019 RF Oscillator Design Introduction

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EE3300: ELECTRONICS 2Assignment 1 – Colpitts Oscillator

Jesse Lee12!0200

"#e: 3$0%$201&'ro#p mem(ers: )ic*ael Sa#n+ers, Nat*an Jo*nston


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ContentsAim------------------------------------------------------------------------------------------------------------------------ 2

T*eor.------------------------------------------------------------------------------------------------------------------- 2

Oscillators-----------------------------------------------------------------------------------------------------------2Oscillator Applications----------------------------------------------------------------------------------------2

Oscillator "esign------------------------------------------------------------------------------------------------ 2

/artle. Oscillator------------------------------------------------------------------------------------------------3

ig#re 1: /artle. Oscillator "esign------------------------------------------------------------------3

Colpitts Oscillator-----------------------------------------------------------------------------------------------

ig#re 1: Colpitts Oscillator------------------------------------------------------------------------------

)et*o+-------------------------------------------------------------------------------------------------------------------%

Sc*ematics------------------------------------------------------------------------------------------------------------ %

Colpitts Oscillator Sc*ematic------------------------------------------------------------------------------%

ig#re 1: Colpitts Oscillator------------------------------------------------------------------------------%

ig#re 2: oer S#ppl.------------------------------------------------------------------------------------&

ig#re 3: #ll Circ#it it* oer S#ppl.-----------------------------------------------------------&

Sim#lation--------------------------------------------------------------------------------------------------------------4

ig#re 1: Colpitts Oscillator re5#enc. Response--------------------------------------------4

ig#re 2: Oscillator +esigne+ it* small in+#ctor an+ large capacitors-----------!

ig#re 3: Tan6 circ#it an+ ee+(ac6 Resistor---------------------------------------------------!

ig#re : 7oltage 8s- Time Circ#it O#tp#t--------------------------------------------------------

ig#re %: Colpitts re5#enc. Response it* 24% Ω ee+(ac6 Resistor--------

ig#re &: 7oltage 8s- Time Circ#it O#tp#t it* &0 Ω ee+(ac6 Resistor-----10

Res#lts an+ "isc#ssion---------------------------------------------------------------------------------------- 10

ig#re 1: C9 it* components---------------------------------------------------------------------10

ig#re 2: Oscilloscope O#tp#t------------------------------------------------------------------------11

ig#re 3: S5#are a8e O#tp#t-----------------------------------------------------------------------12

ig#re : S5#are a8e O#tp#t – "io+e Clipping--------------------------------------------12

Recommen+ation-------------------------------------------------------------------------------------------------13

ig#re 1: T*eoretical S5#are a8e O#tp#t Sc*ematic-----------------------------------13

Concl#sion----------------------------------------------------------------------------------------------------------- 1

Re;erences-----------------------------------------------------------------------------------------------------------1%

1 Jesse Lee12!0200


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AimIn t*is assignment t*e aim is to create a or6ing oscillator t*at ill generate asine a8e o#tp#t signal t*at can also (e con8erte+ into a s5#are a8e signal-

'i8en an inp#t 127 AC signal, it is to (e con8erte+ to a "C signal (. a. o; a

poer s#ppl., +esign o; personal c*oice, t*is is t*en to (e con8erte+ into asin#soi+al a8e t*at oscillates at )/s inp#t,t*e o#tp#t is t*en ;e+ (ac6 into t*e ;re5#enc. selecti8e netor6- I; t*e to

components are in p*ase an+ magnit#+e t*en stea+. state oscillation can occ#r- T*e ampli=er gain can +etermine *et*er t*e oscillations ill gro or +ecrease-

Negati8e resistance oscillators ill not (e loo6e+ at in t*is co#rse- Simpl. p#t,t*ese oscillators loo6 at S11 o; t*e ampli;.ing circ#it- or some ;re5#encies t*is

8al#e ill (e ?1 ca#sing t*e ampli=er to (ecome #nsta(le t*#s alloingoscillations to occ#r- T*ese +e8ices are primaril. #se+ in microa8e oscillation-

Oscillator ApplicationsOscillators are #se+ in a i+e 8ariet. o; applications- Some e@amples o; *ere

t*e. are #se+ to generate signals incl#+e: tele8ision transmitters, cloc6s, ra+iotransmitters, comp#ters an+ m#sic s.nt*esi


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to ;ee+ c*arge (ac6 an+ ;ort* (eteen t*e capacitors- T*ese are o;ten calle+

tan6 circ#its- T*e =lter circ#it is =ne t#ne+ to resonate at a certain ;re5#enc.(ase+ on t*e si


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Colpitts OscillatorA Colpitts oscillator is +isting#is*e+ (. its +esign in t*at t*e ;ee+(ac6 ;rom t*eampli=er is ta6en ;rom a 8oltage +i8i+er ma+e ;rom to capacitors in series

across an in+#ctor- *ile t*e Colpitts resonator is similar to t*e +esign o; /artle.t*e tappe+ D#nction is ma+e o; to capacitors 8ers#s /artle.>s to in+#ctors-

T*is ca#ses an in8erting p*ase s*i;t *ic* is t*en in8erte+ again to pro+#ce t*ere5#ire+ positi8e ;ee+(ac6- er*aps t*e most nota(le ;eat#re o; t*e Colpittsresonator is its goo+ o#tp#t a8e clarit.- T*is is a(le to *appen +#e to t*e to

capacitor>s lo impe+ance pat*s ;or *armonics B-E-, 14-

ig#re 1: Colpitts Oscillator

Bi66ert, 2013

To calc#late t*e resonant ;re5#enc. o; a Colpitts oscillator t*e ;olloing e5#ationis #se+:

f r=1

2π √ LC T where

1

C T =

1

C 1

+1

C 2

Jesse Lee12!0200


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)et*o+1- "esign a poer s#ppl.-2- "esign an ampli=er an+ ;ee+(ac6 circ#it-3- Sim#late t*e +esigne+ circ#its-

- )o+i;. circ#it to allo ;or a 8aria(le o#tp#t signal-%- )o+i;. circ#it to allo ;or sine to s5#are a8e o#tp#t signal-&- "esign an+ (#il+ a *o#sing to (e 3" printe+ ;or t*e circ#it-4- "emonstrate t*e or6ing +e8ice B$0$201&-

Sc*ematicsColpitts Oscillator Sc*ematicIn t*is tas6 a Colpitts oscillator +esign as c*osen +#e to t*e ease at *ic* t*e

;re5#enc. can (e t#ne+ (. c*anging t*e capacitor 8al#es- It is also +iFc#lt tocreate a precise in+#ctor so *a8ing one instea+ o; to o#l+ allo ;or a simpler

an+ more ro(#st (#il+-

ig#re 1: Colpitts Oscillator

T*e circ#it *as (een +esigne+ to (e a common (ase- /ere t*e 8oltage across C

is applie+ to t*e emitter (ase D#nction o; t*e transistor to create oscillations- T*e

resonant ;re5#enc. is calc#late+ to (e:

C T = C 3 C 4

C 3+C 4=1250 pF

f r=1

2π √ LC T =

1

2π √ 1300×10−9

×1250×10−12=3948148.2 Hz≅4 MHz

or sim#lation p#rposes t*is 8al#e is close eno#g* to )/< as it is 6non t*at

t*e sim#lation ill not tr#l. reGect t*e real li;e +esign- T*e circ#it constr#cte+ ill(e t#ne+ as necessar. #ntil )/< oscillation is ac*ie8e+-

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ig#re 2: oer S#ppl.

Figure 2 s*os t*e Alti#m sc*ematic o; t*e poer s#ppl. to (e #se+ to ;ee+

into t*e oscillator circ#it- T*e poer s#ppl. +esign c*osen is a ;#ll a8e recti=erconsisting o;: a /H(ri+ge, smoot*ing capacitors, to transistors in common

emitter con=g#rations to (oost c#rrent, a ener +io+e to cap t*e 8oltage at 127

an+ a potentiometer t*at ill allo ;or a 8aria(le o#tp#t 8oltage-

ig#re 3: #ll Circ#it it* oer S#ppl.

Figure 3 s*os t*e ;#ll Alti#m sc*ematic +esign to (e man#;act#re+- T*e top

rig*t contains t*e oscillator circ#it, t*e (ottom to are t*e poer s#pplies an+t*e top le;t s*os t*e inp#t an+ o#tp#ts o; t*e IC Bintegrate+ circ#it t*at illcon8ert t*e sine to a s5#are a8e-

In t*is +esign it can (e seen t*at t*ere are to poer s#pplies t*at are slig*tl.+ierent- T*e loer poer s#ppl. *as a resisti8e +i8i+er netor6 across t*e

o#tp#t an+ a 8irt#al gro#n+ tap in t*e mi++le o; t*e +i8i+er- T*is is so t*at a K&7an+ H&7 can (e o(taine+ to ;ee+ into an+ t#rn on t*e IC-

& Jesse Lee12!0200


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Sim#lationsing AR "esign En8ironment, Figure 1: Colpitts Oscillator B;romSchematics as sim#late+ to =n+ t*e resonant ;re5#enc. an+ *at t*e o#tp#t

sin#soi+al ;orm loo6e+ li6e-

ig#re 1: Colpitts Oscillator re5#enc. Response

As can (e seen t*is o#tp#t a8e;orm is e@actl. *at as re5#ire+ an+ e@pecte+- T*e pea6 ;re5#enc. response occ#rs at -03)/< Bclose eno#g* to )/< ;or t*e

sim#lation- T*e gain o; t*e circ#it can (e seen on t*e le;t a@is as 1-2% *ic* is

again re5#ire+ meaning t*at oscillations can occ#r Bas gain is ?1- T*e imaginar.response at )/< *as a gain o; 0 *ic* is correct as e e@pect a 1!0 0 s*i;t ;orm

t*e tan6 circ#it an+ anot*er 1!00 ;rom t*e (ase emitter D#nction-

It s*o#l+ also (e note+ t*at t*e spi6e$pea6 at *ic* t*e oscillator resonates

co#l+ (e ma+e smaller or i+er (. c*anging t*e 8al#es on t*e in+#ctor an+

capacitor- To get a 8er. s*arp spi6e a smaller in+#ctance 8al#e o#l+ (e #se+,t*e capacitors o#l+ (e a+D#ste+ accor+ingl. to ma6e s#re t*at oscillationsocc#rre+ at )/t

slip or c*ange-

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ig#re 2: Oscillator +esigne+ it* small in+#ctor an+ large capacitors

T*ro#g* t*e #se o; t*e t#ning ;eat#re in AR #sing a smaller in+#ctor B2%0n/

an+ m#c* larger capacitors B C 3=C 4=12700 pF , a smaller an+ nicer spi6e at

)/< can (e o(taine+- 'ain asi+e, as t*is can (e c*ange+ t*ro#g* t*e ;ee+(ac6

resistor, t*is is a not a practical mo+el +#e to t*e in+#ctor (eing too small- Asmentione+ a(o8e i; 1300n o#l+ (e 1-% t#rns, t*en 2%0n o#l+ simpl. not (e

ac*ie8a(le-

In t*e sim#lations, t*e t#ning ;eat#re o; AR as #se+ e@tensi8el. to +etermine

t*e component 8al#es in t*e circ#it- It as ;o#n+ t*at (. c*anging t*e 8al#es o;

t*e R ;ee+(ac6 resistor t*e gain o; t*e circ#it co#l+ (e controlle+ an+ t*ro#g*c*anging t*e 8al#es o; t*e tan6 circ#it components t*e resonant ;re5#enc. can(e mo8e+ B*ic* is e@pecte+ +#e to t*e resonant ;re5#enc. e5#ation-

ig#re 3: Tan6 circ#it an+ ee+(ac6 Resistor

*en R as ma+e a s*ort t*e gain o; t*e circ#it o#l+ go 8er. *ig* an+ *ileR as open t*e gain o#l+ ne8er (e a(le to get a(o8e 1- 9. setting R to a &0

Ω resistor a gain o; 1-2% is o(taine+ *ic* is a goo+ starting point ;rom t*e

sim#lation-

! Jesse Lee12!0200


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ig#re : 7oltage 8s- Time Circ#it O#tp#t

T*is is t*e o#tp#t a8e;orm o; t*e circ#it o(taine+ (. replacing t*e OSCTESTit* OSCARO9E in AR- As can (e seen t*is is a sin#soi+al a8e it* a pea6

8al#e o; 1-147- T*e ;re5#enc. can (e calc#late+ li6e:

f =1

(353.4−99.47 )×10−9=3938093 Hz≅ 4 MHz

)eaning t*at t*e circ#it is (e*a8ing t*e a. t*at it is ante+ to- /oe8er t*isp#re sine a8e can onl. (e o(taine+ (. increasing t*e ;ee+(ac6 resistor to 24%

Ω - T*is is not alloe+ as t*e pre8io#s circ#it s*oing t*e resonant ;re5#enc.

means t*at t*e gain o#l+ ;all to onl. (arel. a(o8e 1-

ig#re %: Colpitts re5#enc. Response it* 24% Ω ee+(ac6 Resistor

T*is is not accepta(le as t*e real li;e gain ill (e less t*an t*is 8al#e meaningt*at oscillations ill not occ#r-

Jesse Lee12!0200


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/oe8er (. +ecreasing t*e ;ee+(ac6 resistor t*e sine a8e o#tp#t loo6s less an+

less sine an+ more +istortion is a++e+-

ig#re &: 7oltage 8s- Time Circ#it O#tp#t it* &0 Ω ee+(ac6 Resistor

re5#enc. is still )/< *oe8er t*e sine a8e o#tp#t is no longer a per;ectloo6ing a8e- T*e ot*er ;actor to note is t*at (. increasing t*e ;ee+(ac6

resistance Bnicer a8e t*e 8oltage gain is also se8erel. +roppe+- or t*ese

reasons &0 Ω as c*osen as a mi++le gro#n+ *ere t*e gain an+ sine o#tp#t

response ere (ot* accepta(le-

Res#lts an+ "isc#ssionA;ter t*e sim#lations ere r#n an+ t*e circ#it as +eeme+ accepta(le t*e ne@t

step as t*e (#il+ t*e circ#it on an #gl. (oar+ Bcopper s*eet- As e@pecte+ t*eres#lts meas#re+ on a +igital oscilloscope ere not*ing li6e t*e sim#lation *a+

pre+icte+- To =n+ t*e correct 8al#es, *ea+er pins ere sol+ere+ to t*econnections on t*e #gl. (oar+ so t*at capacitors co#l+ (e *ot sappe+- It as

;o#n+ t*at (. i+ening an+ compressing t*e coils on t*e in+#ctor, t*e ;re5#enc.

co#l+ (e =neHt#ne+ to resonate at e@actl. )/


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ig#re 1: C9 it* components

As t*e poer s#ppl. or6e+ an+ t*ere as no nee+ ;or =ne t#ning, t*ose

components ere sol+ere+ +irectl. into t*e (oar+- or t*e oscillator an+ IC*oe8er, *ea+er pins ere sol+ere+ in so t*at t*e components co#l+ (e easil.

sitc*e+ o#t B*ea+ers ere #se+ ;or t*e IC in case it got ;rie+ an+ o#l+ (e

easil. replacea(le-

T*e =nal 8al#es ere:

C 3=221 pF C

4=68 pF L=3.6 μH

T*eoreticall. gi8ing a ;re5#enc. o;:

f r=1

2π √3.6×10−6×221×10

−12×68×10

−12

221×10−12+68×10

−12

=11632343≅11.6 MHz

As pre+icte+ t*e oscillator>s act#al ;re5#enc. is a loer t*an t*e t*eoretical8al#e calc#late+-

11 Jesse Lee12!0200


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ig#re 2: Oscilloscope O#tp#t

Note: there should not be two lines on the bottom of the wave, the

oscilloscope was simpl behaving strangel on this da-

T*e scope s*os t*at t*e pea6 to pea6 8oltage is &-3&7 Bt*is as t*e ma@im#m

ac*ie8a(le 8oltage it* t*e potentiometer an+ an oscillating ;re5#enc. o;-0&!)/


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*ig* or lo as t*e sine oscillates o8er a re;erence 8oltage- T*ere;ore t*ere m#st

still (e iss#es in t*e setH#p o; t*e ±6V "C s#ppl.-

To satis;. t*e tas6 an alternati8e as e@plore+ to o(tain a s5#are a8e- T*esimplest met*o+ as to #se +io+e clipping- 9. #sing to normal +io+es ;acing

t*e opposite a. connecte+ in parallel- A resistor as a++e+ so t*at c#rrent isnot in=nite, an+ a capacitor as a++e+ to smoot* o#t t*e o#tp#t-

ig#re : S5#are a8e O#tp#t – "io+e Clipping

No e *a8e a a8e t*at is no longer sine t*at oscillates at -0044)/


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to 1) resistors in series ill ;orm a 8oltage +i8i+er gi8ing a re;erence &7 in t*e

mi++le *ic* t*e AC ill (e o8erla.e+ on an+ ;e+ into t*e IC Bop amp- olloingt*at anot*er to 1) resistors ill ;orm a 8oltage +i8i+er to ;e+ &7 into t*e

remaining terminal o; t*e IC- T*is s*o#l+ t*eoreticall. gi8e a s5#are a8e at t*e

o#tp#t o; t*e IC-

Side note: ! was unable to get the transient analsis of this model to

run in microcap due to a "singular matri#$ error%

T*e a+8antage o; t*is s.stem is t*at it ill onl. re5#ire 1 poer s#ppl. c#tting+on t*e si


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Concl#sion T*e primar. aim o; t*is tas6 as to create a sin#soi+al a8e ;rom =rst principlest*at *as a resonant ;re5#enc. o; )/


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Re;erencesCoates, E- B2004H201&- Oscillator Basics- Retrie8e+ ;rom Lean a(o#t Electronics:

*ttp:$$-learna(o#tHelectronics-org$Oscillators$osc10-p*p

Colpitts Oscillator - Bn-+-- Retrie8e+ ;rom Electronics T#torials:*ttp:$$-electronicsHt#torials-s$oscillator$colpitts-*tml

Hartley Oscillator - B201&- Retrie8e+ ;rom Electronics T#torials:

*ttp:$$-electronicsHt#torials-s$oscillator$*artle.-*tml

i66ert, C- J- B2013- RF Electronics Design and Simulation. Tons8ille: James

Coo6 ni8ersit.- Retrie8e+ ;rom*ttp:$$researc*online-Dc#-e+#-a#$3233$1$RM20ElectronicsM20"esign

M20an+M20Sim#lation-p+;

Les#r;, J- Bn-+-- Negative Resistance Oscillators- Retrie8e+ ;rom ni8ersit. o; St-

An+res: *ttps:$$-stHan+res-ac-#6$pa$Scots'#i+e$Ra+Com$part%$page1-*tml

-E-, I- )- B14- Practical Oscillator Handboo. O@;or+: Nenes-

Ro#se, )- B200%, Septem(er- Oscillator - Retrie8e+ ;rom *atis-com:*ttp:$$*atis-tec*target-com$+e=nition$oscillator

1& Jesse Lee12!0200

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RF Oscillator Design Introduction