What Exactly Is An Op-Amp? What exactly is an OPerational AMPlifier? Let s define what that component is and look at the parameters of this amazing device. The
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, Jun 18, 2001
What Exactly Is An Op-Amp?
What exactly is an OPerational
AMPlifier? Let's define what that component is and look at the parameters
of this amazing device. The term 'op-amp' was originally used to describe a
chain of high performance dc amplifiers that was used as a basis for the analog
type computers of long ago. The very high gain op-amp IC's our days uses
external feedback networks to control responses. The op-amp without any external
devices is called 'open-loop' mode, refering actually to the so-called 'ideal'
operational amplifier with infinite open-loop gain, input resistance, bandwidth
and a zero output resistance. However, in practice no op-amp can meet these
ideal characteristics. And as you will see, a little later on, there is no such
thing as an ideal op-amp. Since the LM741/NE741/µA741 Op-Amp is the most popular
one, this tutorial is direct associated with this particular type. Nowadays the
741 is a frequency compensated device.
Let's go back in time a bit and
see how this device was developed. The term "operational amplifier" goes all
the way back to about 1943 where this name was mentioned in a paper written by
John R. Ragazzinni with the title "Analysis of Problems in Dynamics" and also
covered the work of technical aid George A. Philbrick. The paper, which was
defined to the work of the U.S. National Defense Research Council, was published
by the IRE in May 1947 and is considered a classic in electronics. The very
first series of modular solid-state op-amps were introduced by Burr-Brown
Research Corporation and G.A. Philbrick Researches Inc. in 1962. The op-amp has
been a workhorse of linear systems ever since. The first op-amp offered to
the public in 1963 was the µA702 manufactured by Fairchild Semiconductors but it
had very weird supply voltages such as +12 and -6volts.
Below in Fig.1
are op-amp symbols as used today. The one on the right is an older way of
drawing it but still used in books like the ARRL (American Radio
Relay Leaque) and older schematics. It is common practice to omit
the power supply connections as they are implied.
Absolute Maximum Parameters: Maximum means
that the op-amp can safely tolerate the maximum ratings as given in the data
section of such op-amp without the possibility of destroying it. The µA741 is a
high performance operational amplifier with high open loop gain, internal
compensation, high common mode range and exceptional temperature stability. The
µA741 is short-circuit protected and allows for nulling of the offset voltage.
Manufactured by Signetics Corporation.
Supply Voltage (- + Vs): The maximum voltage (positive and
negative) that can be safely used to feed the op-amp.
Dissipation (Pd): The maximum power the op-amp is able to
dissipate, by specified ambient temperature (500mW @ <80° C).
Differential Input Voltage (Vid): This is the maximum voltage that
can be applied across the + and - inputs.
Input Voltage (Vicm): The maximum input voltage that can be
simultaneously applied between both input and ground also referred to as the
common-mode voltage. In general, the maximum voltage is equal to the supply
Operating Temperature (Ta): This is the ambient temperature range
for which the op-amp will operate within the manufacutre's specifications.
Note that the military grade version (µA741)has a wider temperature range than
the commercial, or hobbyist, grade version (µA741C).
Output Short-Circuit Duration: This is the amount of time that an
op-amp's ouput can be short-circuited to either supply
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