ELECTRÓNICA

Alfonso Espinosa R.

ESCUELA POLITÉCNICA NACIONAL

Departamento 'de Electrónica

Semana

FET: D é s e r i pe ion Genera i , JFET, MOSFET,C ¡ r c u i t o s e q u i v a l e n t e s , Arr¡ p 1 i f í c a d o rcon fuente común

FET: A m p l i f i c a d o r e s con FFT's. A p l í c .c Í o n e s e s p e c i a l e s cíe FET's.

O p toe 1ec t ron í ca

O r g a n i z a c i ó n de los grupos

Características y polarizac i ó n de los FFT's.

A m p l i f i c a d o r e s con FET's.

! Prueba B i m e s t r a lRespuesta de Frecuencia

Respuesta 'de frecuencia c! e transister e s b i p o l a r e s ,

A p l i c a c i o n e s de optoelectr£n i c a .

Respuesta de frecuencia I

C i r c u i t o s de compensaciónM Prueba B i m e s t r a l

Respuesta d e f recuencia I I

Rea 1 Í men tac ion C i r c u i t o s de compensación

Am p1 í f í c a d o r e s diferencíales,A m p l i f i c a d o r e s operacfonales: caracte-

r í s t i c a s

O s c i l a d o r e s .

Características de a m p l i f i -cadores o p e r a c i ó n a l e s .

10A p l i c a c i o n e s l i n e a l e s cíe am-p l i f i c a d o r e s ope r a c i o n a l e s I ;A m p I ¡ficador, Sumador, R e s t a -do r .

A p l i c a c i o n e s no \e s1 es de a m p l i f i c a -11 dores o p e r a c f o n a l es

12 F i l t r o s a c t i v o s

A p l i c a c i o n e s l i n e a l e s d e am-p l i f i c a d o r e s o pe r a c i o n a l e s IS e g u i d o r de voltaje. I n t e g r ador, A m p l E f i c ¿j dores de v o l t aje a l t e r n o

A p l i c a c i o n e s n o l i n e a l e s d ea m p l i f i c a d o r e s o p e r a c i o n a l e s

13Generadores cié F une JonesI I P ru e b a B i m e s t r a l

Semana de p r á c t i c a s a t r a s a d a s

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ELECTRÓNICA II( • E s p i r?. osa)

1 . DIAGRAMA DE BODE

i , I , Definición

El diagrama de Bode está formado por dos curvas, en escala logarítmica,que muestran G(jf) « Vo/Vi como:

a) G|db = 20 Ig ¡G¡ = f(f) Variación de la amplitud con la frecuencia.b) / G = f (f) Variación del ángulo de f a s e con. la frecuencia.

2. FUNCIONES DE TRANSFERENCIA

2,1. Fu: n_c_i6 n de transfer ene ia_ proporcio nal

Vo RRi + R2

(K<0

G ,, - 20 Ig Kd b

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La curva de fase es una r seta so b r ael eje de 0°

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'ff' IV 10 IB

'ig.l.- Función proporcionala) Circuitob) Diagrama de Bode.

2.2. Función de tran sf er en cía d. e un integrador .

Fig.2,- Diagramade Boded e u n i nt egrador

(Pe ndiente= 20 db/decada= 6 db/octava)

2 3 /. 5 6 8 10 2 .3 /, b b 8 10 2 3 A 5 6 8 10

2.3. Función de transferencia de un difereneiador.

f er ene lador ,

ELECTRÓNICA II(A. Espinosa)

2.4. Función de transferencia de u-n p o I o

F i g . 4 . -

-JO8 10

Fig.5.- Diagrama de Bode

G ( j f )K para £ « f

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Fig.6.- Diagrama de Bodede la función detransferencia deun cero.

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output drivor

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Ftjj. H9,~ Typicat parameters of monolifhicoporaíionol arnplífler

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Analog íilter can beprogramad digitallyby' enunrd M. SmithlineLanunq flusttiitch Corp . Ithuc.a N Y

The f r e q u e n c y response ofan analog active filter can besckucd digi ta l ly , yct w i t h the resotution and accuracyof retuve tuning and the de s tab i l i ty ofcapacit ive tun-ing . The filter aixepis TIL inputs , pennit t ing it to becontrollcd direcily by a computer and mak ing it ideali c i r clcctronically switched systems. Furthermore, thisd i £ i t a l l y programable filier is cost-competítive with me-chi'tnica'jy switched types of ñlters, especially for high-ortk-r f i i l e r functions.

A simple first-order low-pass filter is drawn in (a).The córner frequency of this circuií is determined bythe proportion (a) of the amplifier output voltage (V)that is applied to the feedback capacitor (C). Since ap-plyíng a voltage of magni tude aV to capacitor C pro-duces tli*; same feedback current as applying a voltageof magniuide V to capacitor c\C, the valué of capaci-tor C is tlfcctively muUiplied by o. Therefore, the fil-tei's córner frequency can be written as:

co¡, ~ ]/aRsC

where Rf is the feedback resistor. The over-all de gain ofthe circuit is unañected by loop gain n.

The cffeelive mul t ip l ica t ion of capacitance C by gaina can he used to control the fihei's córner frequency, asshown in (b). ín this circuit, the filter's córner frequencyis delermined by lof í ic inputs through a vohage-dividersetup. Resi.stor Ru is the upper leg of the divider, whilethe K-sistjince of the lower leg is selected by enablingthe appropriate ni. inverter buífer. When a logic inputtums on one of the buíYers, the resistor associated withlh.it biiH'er is shuí ted to ground.

ResiMor RL provides the appropriate bias vollage for(he huifers. The transistor, whiuh is wíred as an einitter-

follower, reduces the rcsist;mce of the voltage dividerthat is reflected forward in series with capacitor C. ThisThevinin cqu iva l en t rcsistancc (R-j) is divided by thecurrent ¡¿aiii (¡i) of the emittcr-folluwer. For the circuitlo opérate proptrly:

R'\*/ji musí be much lesx (han R, || R¡

where R, is the input resistor. Siace the de levéis of boththe bufTers and the transistor are blocked by the capaci-tor, thcre is no need for any bias stabilization circuitry.

If the eílects of biasing resistor RÍ are neglected, pro-gramable gain a can be expressed as:

« - //[/ + (Rt/R*) + ZRiGi]

where Gj represents the conducíance of thosc resistors,Rj through Rn, whose buífers are cnabled. The füter'scórner frequency now becomes:

where:

= 1/RfCI +(Rt

The filter's starting frequency—that is, the córner fre-quency of the filter with none of the logic buífers en-abled—is equa! to Ko;0. And each increment above thisfrequency, as each íogíc buffer is enabled, is equai toco0RaG¡. Since the effects of the enabled bulíers are ad-ditive, the filter can be programed to accept either stan-dard binary codcs or a binary-coded-decimal input. Forthe tompcncnt valúes cited in the figure, o,-0 is 100 radj-ans/second, K is 2, the starting frequency is 200 rad/s,and ihc frequency increment is 250 rad/s.

Moreover, the programing approach that is shownhere can be extended to higher-order filters through theuse of ei ther the standard biquad or state-variable filterconfigura üons.1'8 D

REFERENCE81. AE. Scr.i.Hi, "Acmé hulera Alt MOVIIIQ lowafü SlanM'dilJilion,' tl,:ijronic ProOucts.June 16, 1P?j.2 GE Totwy. J G Graeme. L P Huelwnan, Op«f«ttOnfll 4mpW«'v- Ue&ign ano Appil-caiHJui." McGiaw-íiill ¡.ic , 1871

-15 V

t b )

ÜU1PUI ÜUTPUT

l_<x|lc-tontrüIlíT<í dcqiKwcy raspón**. I he cumei trequency <>l ih¡-

(¡¡si-uní.if lov;-r>riíib liiifi o! KI) tan t¡e vaned by usiny loop ijüín to

n>¡jlin*!y cüp-ji-itiíiice lf¡ (li) t.níi i;; 'lune dicjdcilly throuyti a vuilrigü

dividor íiríHf.geattjiil ! oy;¿ txjMeis control Ihu resiMain:*í oí tliu

IHQ oí thM O ' - í iO f -T , v,'h:-t lite upper ley is íonritíd by it;sibií¡i RHlowetWNjti a buli'M e, fcttyijir,.j, itü ü'.!.ociated (üsisíüi ISQ I - JU

Eleclronlco/Oi 3. 1974 107

«MMNIMMNIMIM

Regulator for op ampspractically powers itself

Here's a rather novel way to build a dual-voltage regu-lator íor powering opcraíional amplif iers that oíl^rsgood traeking, as wcll as low ripple. 'Cracking hctwccnthe two output volt ages is good because on!y onc refer-en ce source is used for both the positive and ncgaiivesides oí' the regulator. Altliough Ihe circuit eniploys twoop amps itself, they are powered by their own ouipius.Furthermore, the circuit's output-current capahilily ison the order of several amperes, and output ripple isheld to less than 1 millivolt peak-to-peak.

The circuit, shown in the ñgure, opérales as a conven-tional series-pass regulator on its positive side to de-

velop í l s f l ? - v o l t u u t p u t Ainpl i f ier Ai is ILSC^ for er-ror-dctcctiun. 'Ihf pass tr.inM:,ior tbr the positiva side i.sbiascd on froni tl)e unregulatcsí 4-20-V inpni supplyvoltaje. The ou tpu l voltagü from aniplificr Aj then ad-justs tln^ transistor's output .

On the negativc side ( 15 v output) of the regulator,anip l i l ie r A-> opermcs as a uni ty-gain tbllower. The passtrans is tor on the negative side is biasetj in a mannei1

similar to ils positive counterpart. T(te valué of the bias-ing resistor for the negative pass transistor is dííl'erentfrom the valué of the biasing resistor for the positivepass transistor in order to bring Aa's output cluser to thenegative supply voltage.

Since anipliíier A;¡ is wired in a follower configura-tion, the reference voltage developed by the zener díodecan be used for both the positive and negative sidos ofthe regulator. The two output voltages, iherefore, trackeach oíher within approximately 50 mv,

With suitable modiíication, the same circuit approachcan be used to build a regulator for devices other thanop amps that require a split supply. Q

2N3712

t l S V O U T

lupply. Hf;Qu!at<ji cuculí fui op arnps OevulOpt í 15 -V OutputS dom a '20 V unfeg'jlated ^OUfe widi lo;/. Ihítri 1 íiiii!,/uü oí nf.plt;. Al

itjgll UH; ftígutelOf ir .• ' , f , j i .uripü i!'-.i.-lt, tli'jy rf;(,í;ive IneW pO'.vef ll'pul' If'.'íi lh«H Ü-vM OUlpUta AífKXtief AI ¿K.!', .j-, ,in Ofn. i fji;'.-f.|.,r. //fiílf

iifi¡ii,!ir:> A; iti a votlage followei I ¡10 suujiu zetier volíago reierence rnüíai¡s ihai tiochwifl is gocxJ t)^i--'/i:.:n t r , e po^.uvü .md ne

lOti

L-ow-draín reguSatorSs batíery life

'•>•/ f. C. Penn

S t a b l e r e g u l a t i o n of ba t íe ry power suppl ics oncer ; q u : r e d dumping cur ren t inlo a zcner diode or sacri-h ' j i n g several volts and mil l iamperes to a th ree - t e rmina lregulator . Powering up voltage-controlled oscillators and• i t h e r supply-sensitive c i rcui ts with balteries becomespractical when the circuit described here regúlales the> u p p l y voltage. Providing ± 1 -mi l l i vo l t regulat ion wi thloads r ang ing from 5 to 55 mi l l iampcres , thc c i rcui tm a in t a in s accuracy even when the batlery vol tage is only50 mv higher than the regulated output , and it drawsra iher less than 1 mA of quiescent current .

As evident in the schematic, the s implici ty of thec i r cu i t belies its performance. The rcgula t ing operationalamp l i f i e r A gets its reference voltage from the bridgeniade up of R, to R3 and a l ight-emit t ing diode. The dropacross the LEO, whíeh varíes from device to device, isabout 1.4 v and it remanís relativcly stable over a wideumperature range. Changing the tempcraturc from:.OT to 40'C varics the regulated-output vol tage onlyabout 1 mv. I f greater s tab i l i ty is requircd , a low-vollagereference diode or even a two- terminal regulator may

be subs t i tu ted for tiie LED in ihc reference Icg of thcbridge.

The op amp controls Q; and Q, to main ta in a /erooffset betwcen its invcr t ing and noninvcr t ing inputs , thuses t ab l i sh ing tha t the voltage drop across R2 ¡s equal tothe drop across thc i , i ;n . The regula ted-output voltage isthc sum of the drops across H, and R3; this can be shownto be VRfcü = V1i : ü (R, /R; + 1). With the valúes tha íappear in the schemat ic and if VL E U = 1.4 v, thcregulated-output vol tage V K E G by s u b s t i t u t i o n becomes1.4(22 k i l o h m s / 1 0 k i lohms + 1} = 4.48 v. If ihcvoltage must be t r immed to a pa r t i cu l a r valué, a 5-küohm potentiometcr can be inscrted bctween R, andRz, w i t h its wiper connected tú the op amp.

Although the op amp is powered by the bus it regu-lates, the c i rcu i í exhibi t s no s tar t -up probíems. As soonas power is applied, Q», biased on by the current throughR6, turns on Q,, supp ly ing power to the op ampand rcference bridge. Q, and Q2, in conjunction w i th R4

and R5, form a feedback pair w i t h a voltage gain ofabout 3. For that reason, a high-gain op amp may beused with no danger of oscülation.

The op amp is ha l f of a dual package, although itcould equa l ly wcll be onc four th of a quad package. Incither casef the regulated bus can power a!l the op ampsin the package, so long as the tota! current requíred doesnot excced 55 m.\ The current drawn by the TLO 22dua l op amp alone is about 800 microamperes. Alsopictured in thc schematic are optional filtering anddecoupling componcnls, Ci, Ci, and R7. Q

4.7S5

55 mA MAX

üíittery aupijlyregulotor.Volfíiíjü drtip acrüf/i ¡ UJ m bddijt; reiefUfo»i 0|.i [<:• dt,.n,t< íu/fj Un-Jci

with suf4.!/vüll.i(ji'íiiíir,ijii«jl.il.; ! ^ul . j ( c, 4 ,'íjíi ): UO I V wilh lo - j f JS f í l f iy iny ffülil ¡) lo í)í) inA 'Jiifi-'ll

í)6 Electronica/Oocember n, I9/ '1