20 February 2006
Performs operations on
V+ and V- power
Can amplify inputs
Open loop operation: a very
small difference between +Vin
V+ and -Vin swings the output
voltage to the corresponding Vref
(V+ or V-)
Open Loop Operation
+15V If V1>V2, Vout=+15V
V1 If V1<V2, Vout=-15V
If V1=V2, Vout=0V
-15V Typical op-amps swing
from V+ to V- with mV
input voltage differences
Closed Loop Operation
Golden Rule 1: The output attempts to make the input
voltage difference zero.
Golden Rule 2: The inputs draw no current.
V+=Vin and V-=V+
Vin/Vout=(R1+R2)/R1 => Non-inverting Amplifier
Infinite open loop gain
Infinite input impedances
(zero input current) V+
Zero output impedance
Zero noise V2
Zero input offset voltage V-
Ideal Op-Amp Typical Op-Amp
Input Resistance infinity 106 (bipolar)
109 - 1012 (FET)
Input Current 0 10-12 – 10-8 A
Output Resistance 0 100 – 1000
Operational Gain infinity 105 - 109
Common Mode Gain 0 10-5
Bandwidth infinity Attenuates and phases at high
frequencies (depends on slew rate)
Temperature independent Bandwidth and gain
Active regions: clipping occurs when the output
Inputs: feedback must be negative for proper
Input difference limits: ignoring limits on input
differences cause harmful current levels.
Cheaper than buying a commercial PID controller.
Saves microcontroller processing time
R1 = R2 = RF
The output signal from an accelerometer can be
integrated once to give a voltage output
proportional to velocity.
This signal can then be integrated again to give a
voltage proportional to position.
This can be much cheaper than other position
measuring devices such as LVDT’s which can
range from $70-$300.
A non-inverting amplifier is typically used to
amplify the small signals from microphones before
the sound can be processed.
Computer sound systems must amplify the
signals from Digital-to-Analog converters before
sending the sound signal to the speakers.
For further information:
The Art of Electronics, Horowitz and Hill
Introduction to Mechatronics and Measurement Systems,
Alciatore and Histand
Electrical Engineering, Hambley
ME 3056 and 4053 lab manual appendices show details of op-
amp circuits used in data acquisition