1 CHAPTER 20 OPERATIONAL AMPLIFIERS (OP-AMPS)

2 Introduction to operational amplifiers Symbol and Terminals

3 The Ideal Op-Amp The ideal op-amp has  Infinite voltage gain  Infinite bandwidth  Infinite input impedance(open)  Zero output impedance

4 The Practical Op-Amp The practical op-amp has:  high voltage gain  wide bandwidth  high input impedance(open)  low output impedance

5 The differential amplifier

6 The differential amplifier (continue) Single-Ended Input

7 The differential amplifier (con’t) Differential Input

8 The differential amplifier (continue) Common-Mode Input

9 Common-Mode Rejection Ratio The measure of an amplifier’s ability to reject common-mode signals is a parameter called the common-mode rejection ratio (CMRR) is the differential gainis the common-mode gain

10 A simple op-amp arrangement

11 OP-AMP PARAMETERS Input offset voltage (V os ) is the differential dc voltage required between the inputs to force the differential output to zero volt

12 OP-AMP PARAMETERS Input bias current is the average of both input currents and is calculated as follow:

13 OP-AMP PARAMETERS Input impedance  The differential input impedance  Common-mode input impedance

14 OP-AMP PARAMETERS Input Offset Current is the difference of the input bias currents, expressed as an absolute value

15 OP-AMP PARAMETERS The output impedance is the resistance viewed from the output terminal of the op- amp

16 OP-AMP PARAMETERS The common-mode input voltage range is the range of input voltages which will not cause clipping or other output distortion Open-Loop Voltage Gain, A ol Open-loop voltage gain is the internal voltage gain of the device and represents the ratio of output voltage to input voltage when there are no external components, and it can range up to 200,000 and is not a well controlled parameters

17 OP-AMP PARAMETERS Common-Mode Rejection Ratio (CMRR)  The accepted definition of CMRR for an op- amp is the open-loop voltage gain A ol divided by the common-mode gain

18 Slew rate The maximum rate of change of the output voltage in response to a step input voltage is the slew rate of an op-amp The slew rate is dependent upon the frequency response of the amplifier stages within the op- amp Slew rate =∆Vout /∆t

19 NEGATIVE FEEDBACK When negative feedback is present, the noninverting and inverting inputs are nearly identical Without negative feedback, an extremely small difference in the two input voltage drives the op-amp to its output limits and it becomes onlinear

20 OP-AMP configurations with negative feedback Closed-Loop Voltage Gain, A cl, is the voltage gain of an op-amp with negative feedback

21 Noninverting amplifier

22 Op-amp voltage-follower A cl(VF) =1

23 Inveting Amplifier