CHAPTER 14 SIGNAL GENERATORS AND WAVEFORM-SHAPING CIRCUITS

Transcription

1 CHAPTE 4 SIGNA GENEATS AN WAEFM-SHAPING CICUITS Chapter utline 4. Baic Principle o Sinuoidal cillator 4. p Amp-C cillator 4. C and Crytal cillator 4.4 Bitable Multiibrator 4.5 Generation o Square and Triangular Waeorm uing Atable Multiibrator 4.6 Generation o a Standardized Pule-The Monotable Multiibrator 4.7 Integrated-Circuit Timer 4.8 Nonlinear Waeorm-Shaping Circuit NTUEE Electronic. H. u 4-

2 Type o cillator inear ocillator: 4. Baic Principle o Sinuoidal cillator Employ a poitie eedback loop coniting o an ampliier and a requency-electie network Some orm o nonlinearity ha to be employed to proide control o the amplitude o the output Nonlinear ocillator: Generate quare, triangular, pule waeorm Employ multiibrator: bitable, atable and monotable The cillator Feedback oop and cillation Criterion Poitie eedback loop analyi: xo A A A, where i the loop gain x A i Characteritic equation: - = Find pole o the cloed-loop ytem by oling = Underdamped j t cillation j t t t Untable j t t NTUEE Electronic. H. u 4-

3 Barkhauen criterion: The phae o loop gain hould be zero at The magnitude o the loop gain hould be unity at The characteritic equation ha root at = j j A j j j j Stability o ocillation requency: i determined olely by the phae characteritic A teep unction reult in a more table requency Stability o ocillation requency: cillation: loop gain A = Growing output: loop gain A > ecaying output: loop gain A < Nonlinear Amplitude Control cillation mechanim: Initiating ocillation: loop gain lightly larger than unity pole in HP Gain control: nonlinear network reduce loop gain to unity pole on j-axi NTUEE Electronic. H. u 4-

4 NTUEE Electronic. H. u imiter Circuit or Amplitude Control For mall output amplitude o, o incremental gain lope = / For large negatie output wing on, o incremental gain lope = 4 / For large poitie output wing o, on incremental gain lope = / A 4-4 / / / / I I I I B / / / / I I I I

5 NTUEE Electronic. H. u 4. P Amp-C cillator Circuit Wien-Bridge cillator eine the loop gain Pole location by oling the characteritic equation cillation condition: - / = and = j = j/c Start-up condition: - / < pole at HP Barkhauen criterion: cillation condition: / = and = /C Start-up condition: = C and / = + imiter i ued or amplitude control C C Z Z Z Z Z Z A p p p p / / and 4-5 / / C C C C and / / C C j C C j C j j

6 Wien-Bridge cillator with Amplitude Control iode are ued to limit the amplitude o the output wing iode are o with mall-ignal operation and can be neglected or analyi o the ocillation condition NTUEE Electronic. H. u 4-6

7 Phae-Shit cillator The circuit ocillate at the requency or which the phae hit o the C network i 8 nly at thi requency will the total phae hit around the loop be or 6 The minimum number o C ection i three K hould be equal to the inere o the magnitude o the C network at ocillation requency Slightly higher K i ued to enure that the ocillation tart imiter i ued or amplitude control NTUEE Electronic. H. u 4-7

8 NTUEE Electronic. H. u Quadrature cillator Baed on the two-integrator loop without damping oop gain: cillation condition: Pole are initially located in HP or < to enure that ocillation tart Too much poitie eedback reult in higher output ditortion i purer than becaue o the iltering action proided by the econd integrator on the peaklimited output o the irt integrator and hae a phae dierence o 9 o due to the integrator unction 4-8 Norton equialent o the t tage i C C C C C C C j j / and C C

9 Actie-Filter Tuned cillator The circuit conit o a high-q bandpa ilter connected in a poitie-eedback loop with a hard limiter Any ilter circuit with poitie gain can be ued to implement the bandpa ilter Can generate high-quality output ine wae Hae independent control o requency, amplitude and ditortion o the output inuoid Final emark p amp-f ocillator ~ to khz ower limit: paie component Upper limit: requency repone and lew rate o op amp NTUEE Electronic. H. u 4-9

10 C Tuned cillator 4. C and Crytal cillator Colpitt ocillator: capacitie diider Hartley ocillator: inductie diider A parallel C circuit between bae and collector model the oerall loe Analyi o Colpitt cillator / C C / / / C / C C c CC C C gm C j gm j C C CC C / CC / C C and gm C Utilize the tranitor nonlinear I- characteritic or amplitude control el-limiting Collector drain current waeorm are ditorted due to the nonlinear characteritic utput oltage i a inuoid with high purity becaue o the iltering action o the C tuned circuit C c g Barkhauen criterion: c m c c NTUEE Electronic. H. u 4-

11 Complete Circuit or a Colpitt cillator C Analyi E AC Analyi NTUEE Electronic. H. u 4-

12 The Cro-Coupled C cillator Popular C ocillator circuit uitable or IC implementation Capable o operating at high requencie up to hundred o GHz The ocillation requency i deined by the C tank The cro-couple pair i to tart up the ocillation ierential ocillation output aailable oop gain: gm / / C Barkhauen criterion: g m j and gm / / j j C C NTUEE Electronic. H. u 4-

13 Crytal cillator Crytal impedance: Z / C Z C p p / C / [ C p C / C C / C C p ] p / / C / C p Z j j C p p Crytal reactance i inductie oer ery narrow requency to p The requency band i well deined or a gien crytal Ue the crytal to replace the inductor o the Colpitt ocillator cillation requency i dominated by C much maller than other C / C Crytal are aailable with reonance requencie KHz ~ hundred MHz The ocillation requency i ixed tuning i not poible NTUEE Electronic. H. u 4-

14 4.4 Bitable Multiibrator Bitable Characteritic Poitie eedback or bitable multiibrator Stable tate: = + and + = + / + = - and + = - / + Metatable tate: = and + = Traner Characteritic o the Inerting Bitable Circuit Initially I = -, the bitable i in the tate o = + and + = + / + change tate to when I increae to a alue o + / + Initially I = +, the bitable i in the tate o = and + = / + change tate to + when I decreae to a alue o / + The circuit exhibit hyterei with a width o TH T Input I i reerred to a a trigger ignal which merely initiate or trigger regeneration NTUEE Electronic. H. u 4-4

15 Traner Characteritic o the Noninerting Bitable Circuit Initially I = -, the bitable i in the tate o = - and + = I / + + / + < change tate to + when I increae to a alue TH that caue + = TH = / > Initially I = +, the bitable i in the tate o = + and + = I / / + > change tate to - when I decreae to a alue T that caue + = T = + / < Application o the Bitable Circuit a a Comparator NTUEE Electronic. H. u 4-5

16 imiter Circuit or Precie utput eel Z Z CC + Z 4 Z - - EE NTUEE Electronic. H. u 4-6

17 4.5 Generation o Square and Triangular Waeorm uing Atable Multiibrator peration o the Atable Multiibrator C charge/dicharge: For = + and + = / + > i charged toward + through C change tage to when = + For = and + = / + < i dicharged toward through C / C e t C ln t change tage to + when = + / ln t / C e T C / ln t / C e T C For = - + : T C ln NTUEE Electronic. H. u 4-7

18 Generation o Triangular Waeorm Triangular can be obtained by replacing the low-pa C circuit with an integrator The bitable circuit required i o the noninerting type TH T T C T C TH T TH T T C T C TH T NTUEE Electronic. H. u 4-8

19 p-amp Monotable Multiibrator Circuit component: Trigger: C, 4 and Clamping diode: 4 >> i 4 The circuit ha one table tate: = + B = and on peration o monotable multiibrator 4.6 Generation o a Standardized Pule The Monotable Multiibrator Negatie tep a the trigger input conduct heaily C i pulled below B or eectie trigger change tate to - and C become negatie and o and C i dicharged toward - change tate to + a B = C = - C i charged toward + B i clamped to and the circuit i back to it table tate Poitie trigger tep turn o inalid trigger B t / C t e T C ln C ln NTUEE Electronic. H. u 4-9

20 4.7 Integrated-Circuit Timer Monotable Multiibrator uing 555 Timer Circuit S Stable tate: S = = and Q = Q on and C = Trigger trigger < T : S = and Q = Q o and C i charged toward CC Trigger pule remoal trigger > T : S = = and Q = Q o and C i charged toward CC End o recoery period C = TH : = and Q = Q on and C i dicharged toward GN Stable tate: C drop to and S = = and Q = C t CC e t / C T C ln. C NTUEE Electronic. H. u 4-

21 Atable Multiibrator uing 555 Timer Circuit T t / C B A C t CC CC T e H C T C ln. 69C C A B ln.69c A B TH e B t / C B B T T T. 69C H TH uty cycle T T H B A A B B peration o atable multiibrator Initially C = : S/ = / and Q = Q o and C i charged toward CC thru A and B C reache TH : S/ = / and Q = Q on and C i dicharged toward GN thru B C reache T : S/ = / and Q = Q o and C i charged toward CC thru A and B NTUEE Electronic. H. u 4-

22 4.8 Nonlinear Waeorm-Shaping Circuit Nonlinear Ampliication Method Ue ampliier with nonlinear traner characteritic to conert triangular wae to ine wae ierential pair with an emitter degeneration reitance can be ued a ine-wae haper Breakpoint Method 4, 5 >>, and to aoid loading eect < IN < : = IN < IN < or < IN < = + IN 5 / IN < or < IN = NTUEE Electronic. H. u 4-