Download V IN

“Op-Amp”
Operational Amplifier
Op-Amp name derives from early usage of these elements in
performing mathematical operations in analog computers.
• Non Inverting Amplifier
• Inverting Amplifier
• Adder
– (and Subtractor using an Inverter)
• Differential Amplifier
• Integrator
• Differentiator
Three Ways to Examine Op-Amp
Behavior
• Consider as an Ideal Op-Amp
Component
• Consider as a Feedback Model
and Examine Behavior
• Perform Conventional Circuit
Analysis
VE = VIN+ - VIN-
VIN-
VIN+
VOUT = a * VE
Ideal Op-Amp Model
VE = VIN+ - VIN-
VOUT = a * VE
Behavior of Feedback Model
Behavior of Feedback Model
of
Non Inverting Amplifier
Behavior of Feedback Model
Behavior of Feedback Model
Behavior of Feedback Model
Behavior of Feedback Model
Summary
Circuit Analysis Approach
Circuit Analysis Approach
“Op-Amp”
Operational Amplifier
Op-Amp name derives from early usage of these elements in
performing mathematical operations in analog computers.
• Non Inverting Amplifier
• Inverting Amplifier
• Adder
– (and Subtractor using an Inverter)
• Differential Amplifier
• Integrator
• Differentiator
Differential Amplifier Circuit Analysis
a (V+ - V-)
Differential Amplifier Circuit Analysis
a (V+ - V-)
Differential Amplifier Circuit Analysis
a (V+ - V-)
Differential Amplifier Circuit Analysis
a (V+ - V-)
Differential Amplifier Circuit Analysis
a (V+ - V-)
 ZF / ZG
Common Mode Rejection
Ratio
v1
v1
v2
vi1
vi2
Original Inputs
vid / 2

vicm
vid / 2
v2
Model of inputs with commonmode and differential-mode
components
Common Mode Rejection Ratio
CMRR
A
CMRR 
Acm
where A is the differential
mode gain and Acm is the
common mode gain
A
CMRRdB  20 log
dB
Acm
Ideally: CMRR
Typically: 60 dB  CMRR  120 dB
Assumes R2 = R4 and R1 = R3
Differential Amplifier Circuit Analysis
with Component Imbalance
Differential Amplifier Circuit Analysis
with Component Imbalance
Differential Amplifier Circuit Analysis
with Component Imbalance
Differential Amplifier Circuit Analysis
with Component Imbalance
Differential Amplifier Circuit Analysis
with Component Imbalance
The Maximum Power Transfer Theorem simply
states, the maximum amount of power will be
dissipated by a load resistance when that load
resistance is equal to the Thevenin/Norton resistance
of the network supplying the power.
To create the Thevenin Equivalent Circuit we need:
1. Value of the Thevenin Voltage Source
2. Value of the Thevenin Resistance
Input and Output
Impedances of
Noninverting Op-amp
Configuration
-
Rai 
Rd vd
ii
vi
The unity gain buffer input
impedance is much higher
than the op-amp input
impedance Rd. The amplifier
output impedance is much
smaller than the op-amp
output impedance Ro.
+
Ro
+
- Avd
vo
io
 Rao
RL
CL
Rai  Rd ( A  1)  Rd A
Rao  Ro /( A  1)  Ro / A
Instrumentation Amplifier
v1
R3
R4
R2
vout
R1
R2
vref
v2
vout - vref 
R3
R4 
R 
1  2 2 v2 - v1 
R3 
R1 
R4
G
vout - vref
v2 - v1
R4 
R2 
 1  2 
R3 
R1 
Instrumentation Amplifier
Example
Burr-Brown INA118
Parameters: R1  RG
vout  Vo
R2  25k
vref  Ref
Gain:
G
Vo - Ref
50k

1

VIN - VINRG
If RG  49.9,
G  1

50,000
 1,003
49.9
R3  R4  60k
v2  VIN
v1  VIN-
Instrumentation Amp (cont.)
A feedback network may also be included with the instrumentation amplifier.
v1
R2
vdiff = v2 - v1
R4
R3
vout
2R1
R2
v2
R3
R4
R
Vout s 
Gs

Vdiff s  s  1
RC
C