In 1968, Fairchild Semiconductor issued the µA748. The
device had essentially the same performance characteristics as the µA741. The
difference was external frequency compensation.
The first multiple op amp device was
Raytheon Semiconductor's RC4558 in 1974. Characteristics of this new device
are similar to the µA741 except that the latter uses NPN input transistors.
Later in that same year, the LM324 quad op amp from National Semiconductor
became public to the delight of manufacturing industry and hobbyist alike. It is
similar in characteristics in comparison with the µA741 in speed and input
current. The LM324 is especially useful for low-power consumption. The beauty of
this chip, according to some engineers, is its single-power-supply requirement.
Now the snowball was rolling. The first FET input op amp was the CA3130 made by
RCA. With this addition to the op-amp family, extremely low input currents
were achieved. Its power can be supplied by a +5 to +15vdc single supply system.
A beautiful piece of work this CA3130.
In July 1975, National Semiconductor came out with the J-FET type LF355. This
was the first device created using ion implantation in an op amp.
Texas Instruments introduced the TL084 op amp in October 1976. It is a quad
JFET input op amp; it also is an ion-implant JFET. Low bias current and high
speed are two of its beautiful attributes.
In dated sequence, the op-amp developed like this: 1963-µA702, 1965-µA709,
1967-LM101/LH101, 1968-µA741, 1974-RC4558/LM324, 1975-CA3130/LF355, and in 1976
the TL084... wow! Most of the mentioned op-amps have of course been replaced
over time, keeping the same model number, with cleaner and low-noise types.
Meaning, the cutting laser of the early 60's was not of the same quality and as
narrow as the 70's or the 80's, etc. Other companies like RCA discontinued their
semiconductor line all together.
Today, and since that month in 1976, the types of op amps have increased almost
daily. We now enjoy a variety of op amps that will provide the user essentially
with anything s/he needs, such as high common-mode rejection, low-input current
frequency compensation, cmos, and short-circuit protection. All a designer has
to do is expressing his needs and is then supplied with the correct type.
Op-Amps are continually being improved, especially in the low-noise areas.
Shown in Fig.1 at the right 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. The µA741 is Manufactured by Fairchild Semiconductor.
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
voltage.
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 voltage.
Summed-up Features:
· Internal Frequency Compensation
· Short Circuit Protection
· Offset voltage null capability
· Excellent temperature stability
· High input voltage range
· NO latch-up
Input Parameters:
Output Parameters:
Dynamic Parameters:
Other Parameters:
Open-Loop Gain & Frequency:
Unlike the ideal op-amp
(Fig. 5-1), the op-amp that is used in more realistic circuits today, does not
have infinite gain and bandwidth. Look at Open-loop gain in Fig. 4 above, it is
graphed for a type 741 op-amp as a function of frequency. At very low
frequencies, the open-loop gain of an op-amp is constant, but starts to taper
off at about 6Hz or so at a rate of -6dB/octave or -20dB/decade (an octave is
a doubling in frequency, and a decade is a ten-fold increase in frequency).
This decrease continues until the gain is unity, or 0 dB. The frequency at which
the gain is unity is called the unity gain frequency or fT. Maybe the first
factor in the consideration of a specific op-amp is its "gain-bandwidth
product" or GBP. For the response curve of Fig. 4, the product of
the open-loop gain and frequency is a constant at any point on the curve, so
that: GBP = AolBW
Graphically, the bandwidth is the point at which the closed-loop gain curve
intersects the open-loop curve, as shown in Fig. 5 for a family of closed-loop
gains. For a more practical design situation, the actual design of an op-amp
circuit should be approximately 1/10 to 1/20 of the open-loop gain at a given
frequency. This ensures that the op-amp will function properly without
distortion. As an example, using the response in Fig. 4, the closed-loop gain at
10Khz should be about 5 to 10, since the open-loop gain is 100 (40dB). One
additional parameter is worth mentioning, the Transient Response, or rise
time is the time that it takes for the output signal to go from 10% to
90% of its final value when a step-function pulse is used as an input signal,
and is specified under close-loop condistions. From electronic circuit theory,
the rise time is related to the bandwidth of the op-amp by the relation: BW
= 0.35 / rise time
Open-Loop Gain:
Lets have a look how the 'ideal' amplifier would look like in Fig. 5-1. The
search for an ideal amplifier is, of course, a futile exercise. The
characteristics of the operational amplifier are good enough, however, to allow
us to treat it as ideal. Below are some amplifier properties that make
this so. (Please realize that these ratings are next to impossible to achieve).
1. Gain--infinite
2. Input impedance--infinite
3. Output impedance--zero
4. Bandwidth--infinite
5. Voltage out--zero (when voltages into
each other are equal)
6. Current entering the amp at either
terminal--extremely small
The "operation" refered to mathematical operations, such as
addition, integration, etc. An exact equivalent of the ideal Op-Amp is called a
"nullor" and it is composed of new elements -- the nullator and the
norator. The input to the opamp is the nullator (i.e. no voltage or
current), while the ouput is the norator (i.e. any voltage or current). These
two components give the device its ideal characteristics.
Power Supply:
In general op-amps are designed to be powered from a dual or bipolar voltage
supply which is typically in the range of +5V to +15Vdc with respect to
ground, and another supply voltage of -5V to -15Vdc with respect to ground,
as shown in Fig. 7. Although in certain cases an op-amp, like the LM3900 and
called a 'Norton Op-Amp', may be powered from a single supply voltage.
Electrical Ratings:
Electrical characteristics for op-amps are usually specified for a certain
(given) supply voltage and ambient temperature. Also, other factors may play an
important role such as certain load and/or source resistance. In general, all
parameters have a typical minimum/maximum value in most cases.
Fig. 6 - The two most common
types are shown in the diagram on the right. Depending on the application, the
8-pin version is used the most, worldwide. Actually, there is a third type in
the form of a metal-can but is obsolete and, by my knowledge, no longer used. I
have two of these metal-can types and keep them as a 'gone-by' memory.
Definition of 741-pin functions: (Refer to the internal 741
schematic of Fig. 3)
Pin 1 (Offset Null): Offset nulling,
see Fig. 11. Since the op-amp is the differential type, input offset voltage
must be controlled so as to minimize offset. Offset voltage is nulled by
application of a voltage of opposite polarity to the ofset. An offset
null-adjustment potentiometer may be used to compensate for offset voltage. The
null-offset potentiometer also compensates for irregularities in the operational
amplifier manufacturing process which may cause an offset. Consequently, the
null potentiometer is recommended for critical applications. See 'Offset Null
Adjustment' for method.
Pin 2 (Inverted Input): All input
signals at this pin will be inverted at output pin 6. Pins 2 and 3 are very
important (obviously) to get the correct input signals or the op amp can not do
its work.
Pin 3 (Non-Inverted Input): All input
signals at this pin will be processed normally without invertion. The rest is
the same as pin 2.
Pin 4 (-V): The V- pin (also referred
to as Vss) is the negative supply voltage terminal. Supply-voltage operating
range for the 741 is -4.5 volts (minimum) to -18 volts (max), and it is
specified for operation between -5 and -15 Vdc. The device will operate
essentially the same over this range of voltages without change in timing
period. Sensitivity of time interval to supply voltage change is low, typically
0.1% per volt. (Note: Do not confuse the -V with ground).
Pin 5 (Offset Null): See pin 1, and
Fig. 11.
Pin 6 (Output): Output signal's
polarity will be the oposite of the input's when this signal is applied to the
op-amp's inverting input. For example, a sine-wave at the inverting input will
output a square-wave in the case of an inverting comparator circuit.
Pin 7 (posV): The V+ pin (also
referred to as Vcc) is the positive supply voltage terminal of the 741 Op-Amp
IC. Supply-voltage operating range for the 741 is +4.5 volts (minimum) to +18
volts (maximum), and it is specified for operation between +5 and +15 Vdc. The
device will operate essentially the same over this range of voltages without
change in timing period. Actually, the most significant operational difference
is the output drive capability, which increases for both current and voltage
range as the supply voltage is increased. Sensitivity of time interval to supply
voltage change is low, typically 0.1% per volt.
Pin 8 (N/C): The 'N/C' stands for
'Not Connected'. There is no other explanation. There is nothing connected to
this pin, it is just there to make it a standard 8-pin package.
Experiments: You are given the opportunity to play with and
analyze experiments to demonstrate the principles, concepts, and applications of
a couple of these basic configured op-amps. If you have already a dual-voltage
power supply (positive/negative), that would make things alot easier for you. If
not, build this Dual Volt Powersupply listed at the bottom of the page to
get you started. This power supply has two non-adjustable voltages; +12Vdc and
-12Vdc. However, in general, a very simple and cheap power supply can be rigged
up with two 9 Volt alkaline batteries and does the job in most, if not all,
cases. Personally I like to approach a project more professionally and build the
dual 12 volt powersupply. Nice project 'in-between' while learning op-amps.
Bread Board Modules:
A bread board module,
or just 'breadboard', is a board manufactured of plastic with a couple 100 tiny
holes with tiny sockets in them connected electrically together and in the
center of the breadboard a grove to hold a plastic panel for leds, pots and
switches. They measure about 6 by 2 inches and come in white, gray and blue. The
blue kind is called 'BimBoard' and made in the UK. I purchased mine back in 1980
from
ElectroSonic in Toronto Canada and its still working fine. The gray and
white models are manufactured in the U.S. and Canada. They all work. Radio Shack
and the European Tandy are both selling their own version and they work fine
too. The Bread Board Design System is also available, if you can afford it, and
would be preferred if you intend to do a lot more experimenting in the future.
This system contains everything you need already build-in, like the powersupply,
jacks, switches, leds, function generator and lots more goodies. Kindah nice to
have everything in one place.
The Norton Op-Amp:
It is not my intention
to confuse you with a different type of op-amp so I will just mention a couple
of points about this op-amp. The Norton op-amp, or current-differencing
amplifier, is designed to operate from a single ended supply. Wow, that is truly
fantastic. You can use a voltage anywhere from +4V to a whopping +36V! The
Norton op-amp referred to here is the LM3900 and is the best known type made by
National Semiconductor. This chip contains four op-amps in a single 14-pin
package. The picture in Fig. 8-b below shows the symbol for the Norton op-amp.
As you may notice it is somewhat different than the normal op-amp symbol. Fig.
8-c shows the major parameters of relevance between the 741 and the 3900
op-amps.
The
Peak Detector
The peak detector is a circuit that "remembers" the peak value of a signal. As
shown in Fig. 9-a, when a positive voltage
is fed to the noninverting input after the capacitor has been momentarily
shorted (reset), the output voltage of the op-amp forward biases the diode and
charges up the capacitor. This charging last until the inverting and
noninverting inputs are at the same voltage, which is equal to the input
voltage. When the noninverting input voltage exceeds the voltage at the
inverting input, which is also the voltage across the capacitor, the capacitor
will charge up to the new peak value. Consequently, the capactor voltage will
always be equal to the greatest positive voltage applied to the noninverting
input.
Once charged, the time that the peak detector "remembers" this peak value is
typically several minutes and depends on the impedance of the load that is
connected to the circuit. Consequently, the capacitor will slowly discharge
towards zero. To minimize this rate of discharge, a voltage follower can be used
to buffer the detector's output from any external load, as shown in
Fig. 9-b. Momentarily shorting the capacitor to
ground will immediately set the output to zero.
The
Comparator
A 'comparator' is circuit that compares an input voltage with a reference
voltage. The ouput of the comparator then indicates whether the input signal is
either above or below the reference voltage. As shown for the basic circuit in
Fig. 9-c(1) , the output voltage approaches the
positive supply voltage when the input signal is slightly greater than the
reference voltage, Vref. When the input is slightly less than the reference, the
op-amp's output approaches the negative supply voltage. Consequently, the exact
threshold is dominated by the op-amp's input offset voltage, which should be
nulled out. Fig. 9-c(2) shows a Led indicator
wich input is connected to the output Vout of the comparator.
Fig. 9-d(left) The output polarity of the op-amp
switches from positive to negative, it is inconvenient to keep reversing the
voltmeter leads to keep polarity correct. One way to overcome that prorblem is
to use an indicatior light to tell the output state. The circuit show on the
left uses a transistor to switch a led on or off depending on the comparator's
output state. When the op-amp output is 8.5 volts, the transistor switches on
the led via the 220 ohm current-limiting resistor. When the output is -8.5 volts
the transistor is cut-off turning off the led. Transistor choice is not
critical; it can be any common type NPN device. Any type of silicon diode will
protect the transistor. Fig. 9-e(right). The
output on pin 6 switches (repeatedly) from positive to negative and so either
bias Q1 (NPN) or Q2 (PNP and activates RL
which is the resistive load. Just a basic circuit to show you what exactly a
'Boosted-Output' circuit does.
The Instrumentation Amplifier
There are many types of op-amps who are designed for a specific purpose like the
Instrumentation Amplifier from Burr-Brown.(see Fig. 10) In this example we are
talking about the 3660J type. It can be used in both balanced and unbalanced
systems, like a Wheastone Bridge circuit. This does not mean in any way that the
instrumentation amp cannot be used for other applications, on the contrary, it
is in many a case prefered because of the unique parameters of this device.
Keep this in mind as a rule-of-thumb:
An operational amplifier circuit will not work at
all unless:
1. External feedback limits the gain or desired
responce to a design value.
2. Both inputs have direct-current return path to
ground of a similar reference.
3. The input frequencies and required gain are well
within the performance limitations of the op-amp used.
Offset Null Adjustment Procedure for the µA741:
Offset null adjustments differ with the application (e.i. Inverting or
Non-Inverting Amplifier). Offset-null potentiometers are not placed on
design schematics as they would detract from a design. For practice, perform the
following Offset Null adjustment if you wish:
1. Adjust the 10K pot(entio)meter to its center position.
2. Connect the potmeter outside leads between pins 1 and 5 of the op-amp.
Make sure that the power is applied to the design application.
3. Connect the wiper of the potmeter to the negative supply voltage.
4. Ensure that input signals are zero or null and that pins 2 and 3 have
a dc return to ground.
5. Measure the output with a dc meter and obtain zero null by adjusting
the potentiometer.
This is just one method and recommended nulling procedure for the µA741 type
op-amp. Always look for, and follow the particular procedure as specified by
that chip manufacturer. Procedures may become obsolete or updated and changed
when improved op-amp versions come on the market.
Burr-Brown:
Look at this beauty at the right. It is a 20-pin 3656AG Isolation Amplifier made
by Burr-Brown. Just wanted to show the chip because of its uniqueness. This gem
measures about 22 x 28mm and is part of my personal collection. The engineers of
Burr-Brown have surely done a marvelous job more than once.
Planning Your Prototype or Experiment:
Planning the layout of your experiments could be important, especially with
large circuits. Use this
[lay-out sheet] to plan your components layout on the bread board, if you
wish. Remove every component and all wires from previous experiments.
Important: Before starting to insert
components into the breadboard, make sure all power and signal connections are
removed and the power source disconnected. And if required, take the glue/dirt
of the components' legs before inserting them into the sockets, it is very hard
if not impossible to get it cleaned out.
A couple circuit examples:
Below are a couple circuit examples you can play and experiment with to
understand the working of a 741 op-amp hands on. If you are serious about
electronics I strongly recommend buying a book or two about Op-Amps for your
experimenting pleasures.
Fig. 12 - Light Sensor
This is a really nice circuit to play with. When there is NO light falling on
the sensor, the relay closes. When light falls on the LDR, the relay opens. To
reverse the situation just exchange LDR and R1. Example uses for this circuit:
Dark-room, Automatic door-lock, closet, Shed Alarm, etc.
Fig. 13 - Smart Continuity Tester
Occasionally you need a continuity test between two points in an electronic
circuit. Unfortunately, most continuity testers are prone to "lie". They don't
do that deliberately, but if they see a small resistance, they still tell
you that you have continuity. They just don't know any better. This unit is
different. If you have continuity it will tell you so. And if you're reading
even a low resistance through a component, the unit will tell you that as well.
The unit uses two 741 op-amps. It offers a short-circuit test current of less
than 200uA. It detects resistance values of less than 10 ohms. Nicest of all, it
will not break down a PN junction. The device has come in handy in my own shop
for debugging electronic circuits.
Fig. 14 - 12V Battery Monitor
The 100 Kilo-ohm trimmer pot controls the set point of this circuit to a 'high'
point like 12.5 or something, so adjust it to the point you wish the LED to
light up. To monitor a 'low' point, and have the led light up when the battery
has drained to a certain point, connect the led (via the 330 ohm resistor) to
ground (in the blue-boxed area). The led is the high-brightness or ultra-bright
type for maximum visibility. The trimpot in the schematic is a 10-turn type for
better accuracy, but basically any type will do.
Fig. 15 - Low Power Amplifier
This is a simple low power amplifier with a single powersupply. The Rx resistor
+ the resistance of the speaker should equal 1000 ohm. Example: speaker is 150
ohm. Rx is 1000 - 150 = 850 ohm. Closest available value is 860 ohm. I know what
your thinking; what about the 30 volt? Is'nt the max 15 volt? Yes, but positive
and negative they combine 30 volt.
Below is the Dual Volt Power Supply to power the op-amps.
Check the output voltages when you are done. You may lower the 220µF caps to
100µF if need be.
Suggested Reading:
"Active Filter Cookbook", by Don Lancaster, 1975, by Howard W. Sams &
CO., Publisher SAMS, ISBN: 0-672-21168-8
"CDA--The New Current Differencing Amplifier", by W.G. Jung, June 1973,
Popular Electronics, pp. 61-66.
"Design of OP-AMP Circuits With Experiments", H.M Berlin, 1987, Howard W.
Sams & Co., Inc. Publisher SAMS. ISBN: 0-672-21537-3
"IC Op-Amp Cookbook", by W.G. Jung, 1974, by Howard W. Sams & CO.,
Publisher SAMS.
"Introductory Experiments in Digital Electronics", by H.M.Berlin (Book
1&2), Howard W. Sams & Co., Inc. Publisher SAMS.
"Logic & Memory Experiments using TTL Integrated Circuits", by H.M.Berlin
(Book 1&2), Howard W. Sams & Co., Inc. Publisher SAMS.
"Operational Amplifiers--Design and Applications", by G.E.Tobey,
J.G.Graeme, and L.P.Huelsman, 1971. Publisher McGraw-Hill.
"The Design of Active Filters, with Experiments", by H.M.Berlin, 1974.
Howard W. Sams & Co., Inc. Publisher SAMS.
"Understanding IC Operational Amplifiers", by R. Melen and H. Garland,
1971. Reston Publishing Co., Publisher RESTON.
"The Art of Electronics", by Horowitz and Hill, 1989, 2nd edition (3rd?),
Cambridge University Press, ISBN: 0-521-37095-7.
Copyright & Credits:
The following business names, mentioned in this tutorial, are Trade Marked and
protected under International Copyright Law #660099:
ARRL - American Radio Relay Leaque, ECG, Fairchild Semiconductor, Howard W. Sams
& CO. Publishing, McGraw-Hill publishing, National Semiconductor, NTE, Philips,
Raytheon Semiconductors, RCA, Reston Publishing, Texas Instruments, Press
Syndicate of the University of Cambridge.
Some excerpts and graphics are used from SAMS Book "Design of Op-Amp Circuits
With Experiments" written by Howard M. Berlin. Re-print with copyright
permission obtained from: Pearson Education, Kiersti Kjonaas, Foreign Rights.
201 West 103rd Street Indianapolis, IN 46200-1007 -- U.S.A. Tel (317) 581-3500
The beautiful picture of the tube op-amp is published here with permission of
Doug Coward, owner of the
"Analog Computer Museum and History Center. Awsome Doug, thank you.