op-amp explorations mike farrell 3/30/2011. outline goals and setup op-amp input current simple...
TRANSCRIPT
Op-Amp Explorations
Mike Farrell
3/30/2011
Outline
• Goals and Setup• Op-Amp Input current• Simple Inverting Amp• Simple Non-Inverting Amp• Combine the two• Non-Ideal Analysis
Goals
• Prove that the ideal Op-Amp model is valid
• Prove that the non-ideal model is more accurate but not necessary.
• Demonstrate how to hook up Op-Amp circuits
Setup
• All Circuits use a LM741C opamp• Power Supply is +- 15V• Ideal Constraints
– In=Ip=0– Vn=Vp– Av=Inf– Rin=Inf– Ro = 0
Op-Amp Input Current Circuit
R1
100k
R2
100k
U1
R3
10k
Vn
Vp
In
Ip
Input Current Results
• Measured Vp and Vn.• I=(0-Vx)/100K (Passive Sign Convention)• All measurements are within spec for data
sheet and very close to ideal.
Ideal 741 Data Sheet
Measured
Vp (mV) 0 -4.34
Vn (mV) 0 -4.56
Ip (nA) 0 80nA typ500nA max
43.4
In (nA) 0 45.6
Inverting Op-Amp Circuit
R1
100k U1
R3
10k
R2
150K
V1
5v
Vn
Vp
Vo
ut
Non-Inverting Op-Amp Circuit
R1
100kU1
R3
10k
R2
150K
V1
5v
R4
100k R5
150K
Vn
Vp
Vo
ut
Non-Inverting/Inverting ResultsInverting Non-Inverting
Ideal (V)
Measured (V)
% Error Ideal (V)
Measured (V)
% Error
Vp 3.00 2.99 .333 3.00 2.97 1.00
Vn 3.00 2.98 .667 3.00 2.99 .333
Vout -7.50 -7.54 .533 7.50 7.48 .667
Combo Op-Amp Circuit
R1
100kU1
R3
10k
R2
150K
V1
5v
R4
100k R5
150K
Vn
Vp
Vo
ut
Combination of Inverting and Non-Inverting Amplifiers
Combo Op-Amp Results with Non-Ideal Calculations
Ideal Measured Non-Ideal Model -- Calculated
(V) (V) % Error (V) % Error
Vp 3.00 2.99 .333 3.00 0
Vn 3.00 2.98 .667 3.00 0
Vout 0 23.2m -- .397u --
Non-Ideal Circuit used for Calculations
R1
100k
R3
10k
R2
150K
V1
5v
R4
100k
R5
150K E1
1e4
Ro
75
Rin
2MegVn
Vp
Vo
ut
Op-Amp
Conclusions
• In and Ip <50nA (~0A)• Vn = Vp• Using realistic Av, Rin, and Ro does
not have a significant effect on voltage error.
• Vout errors all less than 1% from ideal
Slide 14
Questions?