EE3110-AEC-2008-Opamp-Active Filters_R1

EE3110-AEC-2008-Opamp-Active Filters_R1 -...

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EE3110: Analogue Electronic  Circuits Op-Amps & Active Filters
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4. Operational Amplifiers (Op-Amps) 1. Op-amp types Rashid: ch6, 9 v i v i n v i n v i p v i p v o v o v o p v o n S i n g l e   e n d e d   i n p u t , s i n g l e   e n d e d   o u t p u t . F l o a t i n g   i n p u t , s i n g l e   e n d e d   o u t p u t . F l o a t i n g   i n p u t , f l o a t i n g   o u t p u t . ( + ) ( - )
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- V C C ( + ) ( - ) - + + V C C v i p v o n v o p v i n P r i m i t i v e   O p - A m p
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1. Floating Input, Single Ended Output Op-Amp Static input/output characteristics v i n + V C C - V C C v i p v o v = v - v i d i p i n v ( n e g ) s a t v ( p o s ) s a t v o
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Dynamic characteristics : frequency response  1 0 6 1 0 5 1 0 4 1 0 3 1 0 2 1 0 1 1 1 0 1 0 0 1 k 1 0 k 1 0 0 k 1 M 1 0 M S l o p e   :   6 d B / o c t a v e o r   2 0 d B / d e c a d e A v 0 f c 0 A v f c f B f ( H z )
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The open loop gain  A vo  is finite and decreases with  frequency at the cut-off frequency  f co . When negative feedback is used, bandwidth  f c  can be  increased at the expense of lower gain  A v . In general: 741 op-amp typical values: Product Bandwidth Gain GBW f f A f A B c v c v = = = 0 0 MHz f Hz f A B c v 1 5 000 , 200 0 0
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Slew Rate The output of an op-amp cannot change faster than a  certain value (0.5V/ms for 741) known as the slew rate. The response is a linear change because the mechanism  of slewing involves the charging of compensation  capacitors (internal to the 741) by what looks like a  constant current source. Slew rate v i p v o s V dt t dv S / ) ( 0 =
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Common Mode Rejection Ratio (CMRR) common mode input differential mode input common mode gain common mode rejection ratio this simplified definition is a measure of an amplifier’s  ability to reject unwanted signals that are common to  both inputs. 2 in ip c v v v + = in ip d v v v - = 0 = = d v c o c v v A c v A A CMRR o =
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The Ideal Op-Amp  v i p r o r d v = v - v d i p i n A v v d v i n v o Ideal Bipolar FET i/p A v 200,000 100,000 r d 2M 1T R o 0 80 1-50 CMRR 90dB 100dB f B 1.5MHz 4MHz
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I I O V I O I B I B 1. Deviations From Ideal (offsets and bias currents) I B : bias current required for  input transistor. (for npn, the  current flows into the inputs) I IO : input off-set current,  represents the difference  between the two bias  currents. V IO : input off-set voltage,  input voltage required to  force the output to zero. Category Type V IO I B I IO LM741C General purpose Bipolar 2mV 80pA 20nA LM10 Low supply Bipolar 0.3mV 10pA 0.25nA LF411A Low off-set JFET 0.3mV 50pA 25pA LMC660C Low i/p current CMOS 6mV 2pA 1pA
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Compensation for V IO , I B  and I IO : Quite often the use of  compensation techniques make the temperature even worse.  So sometimes it is better to buy a more expensive op-amp with  a better specification.
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This note was uploaded on 01/11/2011 for the course EE 3110 taught by Professor Wingshingchan during the Fall '08 term at City University of Hong Kong.

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EE3110-AEC-2008-Opamp-Active Filters_R1 -...

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