Analog & Digital Electronics Course No: PH-218

Transcription

1 Analg & Digital Electrnics Curse N: PH-8 Lec-4: Operatal Amplifiers and Filters Circuits Curse Instructr: Dr. A. P. AJPEYI Department f Physics, Indian Institute f Technlgy Guwahati, India

2 Cmparatr as a A/D cnverter Parallel cmparatrs are used t cmpare the lear put signal with varius reference vltage develped by vltage divider. When the put vltage is higher than the reference vltage, a high level is prduced at the cmparatrs utput. The reference vltage fr each cmparatr is set by the vltage divider and reference vltage. Output f each cmparatr is cnnected t an put f the encder that prduces a bary number representg the highest value put. Fr a n digit bary, n cmparatrs are required. Simultaneus r flash methd

3 Summg Amplifier as D/A cnverter A digital t analg (D/A) cnverter is a weighted summg circuit that prduces an utput equal t the weighted sum f puts. The weight is same as the ga f the channel. f f f ( a + b + c ) a b c Bary Input Output ut

4 ltage Substractr r Difference Amplifier Applyg KCL at nde a, 3 3 Applyg KCL at nde b, 3 ) ( + () ) ( ) ( () Subtractg eqn. () frm eqn.()

5 Op-AMP Differentiatr A circuit which the utput vltage wavefrm is the differentiat f put vltage is called differentiatr i i f C d ( 0) 0 C d( ) The put signal will be differentiated prperly if the time perid T f the put signal is larger than r equal t f C As the frequency changes, the ga changes. Als at higher frequencies the circuit is highly susceptible at high frequency nise and nise gets amplified. Bth the high frequency nise and prblem can be crrected by addg, few cmpnents. 5

6 Op-AMP Differentiatr Suppse put signal is susidal. A S (ω t) Then d( ) AωCs( ωt) The amplitude f utput vltage (A Aω) is funct f frequency i.e..a is higher at higher frequency and lwer at lwer frequency. At higher frequencies, signal will be buried side the nise because nise cntas all the frequencies frm lw t high and high frequency nise will be mre amplified at the utput cmpare t the signal. T avid this we use a extra resistr and capacitr series t reduce the strength f nise signal. 6

7 Differentiatr as well as High pass Filter As a Differentiatr i dq d( C ) C d As a high pass filter ( ) X c + v v i Z Z + Z C j ωc j ωc At high frequencies: ω is large, vltage ga At lw frequencies: ω is small, vltage ga 0 7

8 Op-AMP Integratr A circuit which the utput vltage wavefrm is the tegral f the put vltage wavefrm is called tegratr. Here, the feedback element is a capacitr. The current drawn by OPAMP is zer and is virtually grunded i i f 0 C d (0 ) Integratg bth sides with respect t time frm 0 t t, we get t 0 t 0 C d C t 0 Fr accurate tegrat, the time perid f the put signal T must be lnger than r equal t C. 8

9 Op-AMP Integratr Calculate the utput vltage f p-amp tegratr if an put signal f khz, 5 peak amplitude square wave is applied at vertg termal. The value f resistr and capacitr is 0k hm and 0.µF respectively. C t 0 T / 3 T T f 9

10 Integratr as well as Lw pass Filter As a Integratr Q i C C Q C C C As a lw pass filter X C ( ) X c + v v i Z ZC + Z C j ωc j ωc + jωc At high frequencies: ω is large, vltage ga 0 At lw frequencies: ω is small, vltage ga 0

11 Band pass Filter Band pass filter can be btaed by cmbg high frequency filter and lw frequency filter.

12 Filter Circuits An ideal filter wuld have cnstant ga and zer phase shift fr frequencies with its pass band, and zer ga fr frequencies utside this range (its stp band) eal filters d nt have these idealized characteristics.

13 Active Filter Circuits Cmbg an p-amp with suitable resistrs and capacitrs can prduce a range f filter characteristics. These are termed active filters 3

14 Active Filter Circuits Cmmn frms clude: Butterwrth ptimised fr a flat respnse Chebyshev ptimised fr a sharp knee Bessel ptimised fr its phase respnse 4