Lecture 11 Operational Amplifiers Microelectric Circuit by Meiling

Lecture 11 Operational Amplifiers Microelectric Circuit by Meiling CHEN 1

Topics • Ideal op Amplifiers • Ideal OPA circuits analysis • Non-ideal op amplifiers • Non-ideal OPA circuit analysis Microelectric Circuit by Meiling CHEN 2

Ideal operational amplifier Ideal OPA characters 1. 2. 3. 4. 5. Infinite input impedance Zero output impedance Infinite bandwidth Infinite open-loop gain Zero common-mode gain (infinite CMRR) Microelectric Circuit by Meiling CHEN 3

Microelectric Circuit by Meiling CHEN 4

Microelectric Circuit by Meiling CHEN 5

Negative feedback Positive feedback Microelectric Circuit by Meiling CHEN 6

Ideal OPA characters Non-ideal cases Microelectric Circuit by Meiling CHEN 7

Consider finite open-loop gain Microelectric Circuit by Meiling CHEN 8

Input and output resistance Example 2. 1 An impractically large value So we may have the problem of input resistance. Microelectric Circuit by Meiling CHEN 9

Output resistance Microelectric Circuit by Meiling CHEN 10

Example 2. 2 Comparing with Example 2. 1 Design a amplifier with a gain – 100 and an input resistance of 1 M. Example 2. 2: Example 2. 1: Microelectric Circuit by Meiling CHEN 11

Exercise 2. 6 Microelectric Circuit by Meiling CHEN 12

Weighted summer Microelectric Circuit by Meiling CHEN 13

Exercise D 2. 8 Microelectric Circuit by Meiling CHEN 14

Non-inverting amplifier Ideal case: Non-ideal case: Microelectric Circuit by Meiling CHEN 15

Voltage follower Microelectric Circuit by Meiling CHEN 16

Exercise D 2. 9 Exercise D 2. 13 Microelectric Circuit by Meiling CHEN 17

Why use difference amplifier ? CMRR ( Common-Mode Rejection ratio ) Different-mode input Microelectric Circuit by Meiling CHEN Common-mode input 18

Difference Amplifier Method I: Microelectric Circuit by Meiling CHEN 19

Different-mode input Method I: superposition Microelectric Circuit by Meiling CHEN 20

Common-mode input CMRR=infinite Microelectric Circuit by Meiling CHEN 21

Consider the problem of input resistance Differential mode input resistance Microelectric Circuit by Meiling CHEN 22

Instrumentation Amplifier Not is differential mode, common mode input can be pass. Defects: 1. Common mode gain=differential mode gain. 2. Resistance have to match. Advantages: Big differential gain Microelectric Circuit by Meiling CHEN 23

Remove the point x Microelectric Circuit by Meiling CHEN 24

DC non-ideal characters 1. 2. 3. 4. Finite open loop gain ( finite CMRR) Finite BW Offset voltage Input bias and offset current Microelectric Circuit by Meiling CHEN 25

Frequency response (open-loop) Microelectric Circuit by Meiling CHEN 26

Frequency response (closed loop) Microelectric Circuit by Meiling CHEN 27

Output voltage saturation Microelectric Circuit by Meiling CHEN 28

Slew rate Microelectric Circuit by Meiling CHEN 29

Offset voltage From the component mismatches in the input differential stage Output = + saturation or - saturation May be positive or negative Microelectric Circuit by Meiling CHEN 30

1. Reduce the allowable signal swing 2. When input is dc we would not know the output is due to vos or signals Microelectric Circuit by Meiling CHEN 31

Solution 1: Offset-nulling terminals Solution 2: Capacitive coupling (only ac signal be amplified) Microelectric Circuit by Meiling CHEN 32

Offset current Input bias currents Input offset current Upper limit R 2 Microelectric Circuit by Meiling CHEN 33

Solution : introducing R 3 Microelectric Circuit by Meiling CHEN 34

Inverse amplifier Reduce the effect of Vos Reduce the effect of Ios Non-inverse amplifier Reduce the effect of Vos Reduce the effect of Ios Microelectric Circuit by Meiling CHEN 35

Integrator & Differentiator Microelectric Circuit by Meiling CHEN 36

Microelectric Circuit by Meiling CHEN 37

Miller Integrator Microelectric Circuit by Meiling CHEN 38

Consider Vos offset voltage Consider Ios offset current Microelectric Circuit by Meiling CHEN 39

Solution : Microelectric Circuit by Meiling CHEN 40

Microelectric Circuit by Meiling CHEN 41

Example 2. 7 sketch output response Case I: Case II: Microelectric Circuit by Meiling CHEN 42

Differentiator Microelectric Circuit by Meiling CHEN 43

Problem *2. 31 Microelectric Circuit by Meiling CHEN 44

Problem *2. 43 Microelectric Circuit by Meiling CHEN 45

Problem **2. 69 Microelectric Circuit by Meiling CHEN 46

Problem *2. 77 Microelectric Circuit by Meiling CHEN 47

Problem *2. 78 Microelectric Circuit by Meiling CHEN 48

Problem C*2. 126 Microelectric Circuit by Meiling CHEN 49

Non-ideal OP amplifiers 1. Type A: Finite open-loop gain (unknown) 2. Type B: Finite open-loop gain = K 3. Type C: 1. 2. 3. 4. 5. Infinite input impedance Zero output impedance Zero common-mode gain Infinite open-loop gain Infinite bandwidth Ideal OPA characters Microelectric Circuit by Meiling CHEN 50

Type A: Finite open-loop gain (unknown) Microelectric Circuit by Meiling CHEN 51

Type B: Finite open-loop gain =K Microelectric Circuit by Meiling CHEN 52

Type C: ± ± Microelectric Circuit by Meiling CHEN 53