Announcements. Assignment 3 due now, or by tomorrow 5pm in my mailbox Assignment 4 posted, due next week Thursday in class, or Friday 5pm in my mailbox midterm: Thursday, October 27 th. Lecture 11 Overview. Amplifier impedance The operational amplifier Ideal opamp Negative feedback
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ROUT
VOUT
VIN
RIN
AVIN
RS
ROUT
RIN
VOUT
AVIN
VIN
VS
RS
ROUT
RL
RIN
AVIN
VIN
VOUT
VS
+
RL
vout

Ideal opampSo the equivalent circuit of an ideal opamp looks like this:
Originally developed for use in analog computers:
http://www.youtube.com/watch?v=PBILL8UypHA
Originally developed for use in analog computers:
http://www.youtube.com/watch?v=PBILL8UypHA
Take A=106, R1=9R, R2=R
>>1
1) No current flows into the opamp
2) v+ ≈ v
Useful interface between different circuits:
Has minimum effect on previous and next circuit in signal chain
RS
ROUT
RL
RIN
AVIN
VIN
VOUT
VS
v+ grounded, so:
http://www.picotech.com/applications/ecg.html
The AD624AD is an instrumentation amplifier  this is a high gain, dc coupled differential amplifier with a high input impedance and high CMRR (the chip actually contains a few opamps)