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SUNY–Buffalo | Electrical Engineering
EE 311 Electronic Devices & Circuits 2
Lecture 31 | Chapter 13 | 1/1 | 1/5
SUNY–Buffalo | Electrical Engineering
EE 311 Electronic Devices & Circuits 2
Lecture 31 | Chapter 13 | 1/1 | 2/5
Brief History of uA741
EE 311
Electronic Devices & Circuits 2
Lecture 31
Chapter 13
Operational-Amplifier Circuits
● 1964 – Bob Widlar designs the first op-amp: the 702.


● 1965 – Bob Widlar designs the 709 op-amp which more closely
resembles the current uA741


Kwang W. Oh, Ph.D., Associate Professor
SMALL (Sensors & MicroActuators Learning Lab)
Department of Electrical Engineering
University at Buffalo, The State University of New York
113C Davis Hall, Buffalo, NY 14260-1920
Tel: (716) 645-1025, Fax: (716) 645-3656
kwangoh@buffalo.edu, http://www.SMALL.Buffalo.edu
SUNY–Buffalo | Electrical Engineering
EE 311 Electronic Devices & Circuits 2
Lecture 31 | Chapter 13 | 1/1 | 3/5
Using only 9 transistors, it attains a gain of over 1,000
Highly expensive: $300 per op-amp
This op-amp achieves an open-loop gain of around 60,000.
The 709’s largest flaw was its lack of short circuit protection.
● After Widlar left Fairchild, Dave Fullagar continued op-amp design
and came up with the uA741 which is the most popular operational
amplifier of all time.
This design’s basic architecture is almost identical to Widlar’s 309 op-amp with one
major difference: the inclusion of a fixed internal compensation capacitor (30
pF).
 This capacitor allows the uA741 to be used without any additional, external
circuitry, unlike its predecessors.
 The other main difference is the addition of extra transistors for short circuit
protection.
 This op-amp has a gain of around 250,000

SUNY–Buffalo | Electrical Engineering
EE 311 Electronic Devices & Circuits 2
Lecture 31 | Chapter 13 | 1/1 | 4/5
The 741 BJT OP Amp
Figure 13.14 The 741
op-amp circuit: Q11,
Q12, and R5 generate a
reference bias current,
IREF. Q10, Q9, and Q8
bias the input stage,
which is composed of
Q1 to Q7. The second
gain stage is
composed of Q16 and
Q17 with Q13B acting as
active load. The class
AB output stage is
formed by Q14 and Q20
with biasing devices
Q13A, Q18, and Q19,
and an input buffer
Q23. Transistors Q15,
Q21, Q24, and Q22
serve to protect the
amplifier against
output short circuits
and are normally cut
off.
● Reference Bias Current: Q11, Q12
(pp.1032)

● Input-Stage Bias: Q10, Q9, Q8 (Widlar current source)
ln

(Ex.13.15)
● Differential Input Bias: Q1, Q2, Q3, Q4, Q5, Q6

2
, , ,
≅
(Ex.13.16, Fig.13.15)
● Compensation: Q7

ln
V
,
,
≅
≅
(Ex.13.18)
SUNY–Buffalo | Electrical Engineering
EE 311 Electronic Devices & Circuits 2
Lecture 31 | Chapter 13 | 1/1 | 5/5
● 2nd Stage Bias: Q13B, Q17, Q16
0.75

,
≅
,V
,
,
,
ln
,
,
(Ex.13.21)
● Output Stage Bias: Q13A, Q23, Q18, Q19, Q14, Q20

0.25
(Example 13.3, Ex.13.22)
,