Project electronic

Project Report 2011

Table of Contents

i) Amplifiers……….………………………………………………………………02
ii) Ideal amplifier……………………….………………………………………….03
iii) An introduction to the operational amplifier………………….……………...04
(1) Ideal
characteristics.……………………………………………………………..05
(2) Practical
characteristics………………………..…………………….………………06
iv) Limitations of the op-amp……………………………………..………………06
v) Applications of OP-AMPS……………………………………..……………...06
(1) As an
Integrator……………………………………………………………………07
(2) As a
Differentiator………………………………………………………………..10
(3) As an
Inverter………………………………………………………………………13
vi) As a Comparator…………………….…………………………………………17
vii) Overview of uA741 ……………………………………………………………18
viii)Given Task……………………………………………………………………...20
ix) Problems regarding Project and their Solutions……………………………20
x) Future Direction………………………………………………………………...23
xi) References……………………………………………………………………...24

Chapter: Operational amplifiers

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Amplifiers
In "Electronics", signal amplifiers are widely used devices as they have the ability to
amplify a relatively small input signal, for example from a Sensor such as a
microphone, into a much larger output signal to drive a Relay, lamp or loudspeaker
There are many forms of electronic circuits classed as amplifiers.

Amplifiers can be thought of as a simple box or block containing the amplifying
device, such as a Transistor, Field Effect Transistor or Op-amp, which has two input
terminals and two output terminals (ground being common) with the output signal
being much greater than that of the input signal as it has been "Amplified”. An ideal
amplifier has three main properties, Input Resistance or ( Rin ), Output Resistance or
( Rout ) and of course amplification known commonly as Gain or ( A ). No matter
how complicated an amplifier circuit is, a general amplifier model can be used to
show the relationship of these three properties.

Amplifier Gain

Then the gain of an amplifier can be said to be the relationship that exists between
the signals measured at the output with the signal measured at the input. There are
three different kinds of Amplifier Gain, Voltage Gain, ( Av ), Current Gain ( Ai ) and
Power Gain ( Ap ) and examples of these are given below.

Amplifier Gain of the Input Signal

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Voltage Amplifier Gain

Current Amplifier Gain

Power Amplifier Gain

Amplifier Efficiency

Ideal Amplifier
We can know specify the characteristics for an ideal amplifier from our discussion
above with regards to its Gain, meaning voltage gain:

1. The amplifiers gain, ( A ) should remain constant for varying values of
input signal.
2. Gain is not be affected by frequency. Signals of all frequencies must be
amplified by exactly the same amount.
3. The amplifiers gain must not add noise to the output signal. It should
remove any noise that is already exists in the input signal.
4. The amplifiers gain should not be affected by changes in temperature
giving good temperature stability.
5. The gain of the amplifier must remain stable over long periods of time.

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An Introduction to the Operational Amplifier
An operational amplifier IC is a solid-state integrated circuit that uses external
feedback to control its functions. It is one of the most versatile devices in all of
electronics.

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,
referring actually to the so-called 'ideal' operational amplifier with infinite open-loop
gain, input resistance, bandwidth and a zero output resistance.

Operational amplifiers are linear devices that have all the properties required for
nearly ideal DC amplification and are therefore used extensively in signal
conditioning, filtering or to perform mathematical operations such as add, subtract,
integration and differentiation. An ideal Operational Amplifier is basically a three-
terminal device which consists of two high impedance inputs, one called the Inverting
Input, marked with a negative sign, ("-") and the other one called the Non-inverting
Input, marked with a positive plus sign ("+").

The third terminal represents the op-amps output port which can both sink and
source either a voltage or a current. In a linear operational amplifier, the output
signal is the amplification factor, known as the amplifiers gain (A) multiplied by the
value of the input signal and depending on the nature of these input and output
signals

Equivalent Circuit for Ideal Operational Amplifiers

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Op-amp Idealized Characteristics
PARAMETER IDEALIZED CHARACTERISTIC
I. Open Loop Gain, Infinite - The main function of an
(Avo) operational amplifier is to amplify the input
signal and the more open loop gain it has
the better. Open-loop gain is the gain of
the op-amp without positive or negative
feedback and for an ideal amplifier the gain
will be infinite but typical real values range
from about 20,000 to 200,000.

II. Input impedance, (Zin) Infinite - Input impedance is the ratio of
input voltage to input current and is
assumed to be infinite to prevent any
current flowing from the source supply into
the amplifiers input circuitry (Iin =0). Real
op-amps have input leakage currents from
a few pico-amps to a few milli-amps.

III. Output impedance, Zero - The output impedance of the ideal
(Zout) operational amplifier is assumed to be zero
acting as a perfect internal voltage source
with no internal resistance so that it can
supply as much current as necessary to
the load. This internal resistance is
effectively in series with the load thereby
reducing the output voltage available to the
load. Real op-amps have output-
impedance in the 100-20Ω range.

IV. Bandwidth, (BW) Infinite - An ideal operational amplifier has
an infinite frequency response and can
amplify any frequency signal from DC to
the highest AC frequencies so it is
therefore assumed to have an infinite
bandwidth. With real op-amps, the
bandwidth is limited by the Gain-Bandwidth
product (GB), which is equal to the
frequency where the amplifiers gain
becomes unity.

V. Offset Voltage, (Vio) Zero - The amplifiers output will be zero

when the voltage difference between the
inverting and the non-inverting inputs is
zero, or inputs are grounded.

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Op-amp Practilized Characteristics
PARAMETER PRACTILIZED CHARACTERISTIC
I. Open Loop Gain, (Avo) : High
II. Input impedance, (Zin): High
III. Output impedance, (Zout): Low
IV. Bandwidth, (BW): High
V. Offset Voltage, (Vio): Low

Limitations of Op-amp
Some of the limitations that an operational amplifier has are listed below:

1. Use of two additional batteries
2. Operative on low frequencies
3. Gain is limited
4. The input current isn't exactly zero.
5. The input offset current isn't exactly zero either.
6. The input impedance isn't infinite.
7. There is a limited common mode voltage range.
8. The output impedance isn't zero.
9. There are voltage gain limitations including phase shifts.
10. There is a finite input offset voltage.
11. There is a finite slew rate.
12. There is some temperature dependence.
13. They are not the power amplifier.

Applications of the Op-amp

Operational amplifier is used widely in many applications such as:

A. Integrator
B. Differentiator
C. Inverter
D. Comparator

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 As an Integrator:

The integrator does just what the name implies. It integrates - in the calculus sense -
the input signal to produce the output signal. There is a scaling factor and a minus
sign again, but that's pretty much what happens.

Here's the analysis. We make the usual assumptions:

V- = 0

We assume that the input voltage at the inverting input is a virtual ground.

We assume that no current enters the input terminals of the op-amp.

Then, we have - after we write KCL:

C(dVout/dt) + V1/R = 0

C(dVout/dt) + V1/R = 0

Then:


Integrator Amplifier Circuit

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As its name implies, the Integrator Amplifier is an operational amplifier circuit that
performs the mathematical operation of Integration that is we can cause the output to
respond to changes in the input voltage over time. The integrator amplifier acts like a
storage element that

"PRODUCES A VOLTAGE OUTPUT WHICH IS PROPORTIONAL TO THE
INTEGRAL OF ITS INPUT VOLTAGE WITH RESPECT TO TIME".

In other words the magnitude of the output signal is determined by the length of time
a voltage is present at its input as the current through the feedback loop charges or
discharges the capacitor as the required negative feedback occurs through the
capacitor.

When a voltage, Vin is firstly applied to the input of an integrating amplifier, the
uncharged capacitor C has very little resistance and acts a bit like a short circuit
(voltage follower circuit) giving an overall gain of less than one. No current flows into
the amplifiers input and point X is a virtual earth resulting in zero output. As the
feedback capacitor C begins to charge up, its reactance Xc decreases this results in
the ratio of Xc/Rin increasing producing an output voltage that continues to increase
until the capacitor is fully charged.

At this point the capacitor acts as an open circuit, blocking anymore flow of DC
current. The ratio of feedback capacitor to input resistor (Xc/Rin) is now infinite
resulting in infinite gain. The result of this high gain (similar to the op-amps open-
loop gain), is that the output of the amplifier goes into saturation as shown below.
(Saturation occurs when the output voltage of the amplifier swings heavily to one
voltage supply rail or the other with little or no control in between).


The rate at which the output voltage increases (the rate of change) is determined by
the value of the resistor and the capacitor, "RC time constant". By changing this RC
time constant value, either by changing the value of the Capacitor, C or the Resistor,
R, the time in which it takes the output voltage to reach saturation can also be
changed for example.

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If we apply a constantly changing input signal such as a square wave to the input of
an Integrator Amplifier then the capacitor will charge and discharge in response to
changes in the input signal. This results in the output signal being that of a saw tooth
waveform whose frequency is dependent upon the RC time constant of the
resistor/capacitor combination. This type of circuit is also known as a Ramp
Generator and the transfer function is given below.

Ramp Generator

We know from first principals that the voltage on the plates of a capacitor is equal to
the charge on the capacitor divided by its capacitance giving Q/C. Then the voltage
across the capacitor is output Vout therefore: -Vout = Q/C. If the capacitor is
charging and discharging, the rate of charge of voltage across the capacitor is given
as:


But dQ/dt is electric current and since the node voltage of the integrating op-amp at
its inverting input terminal is zero, X = 0, the input current I(in) flowing through the
input resistor, Rin is given as:

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The current flowing through the feedback capacitor C is given as:

Assuming that the input impedance of the op-amp is infinite (ideal op-amp), no
current flows into the op-amp terminal. Therefore, the nodal equation at the inverting
input terminal is given as:

From which we derive an ideal voltage output for the Integrator Amplifier as:

To simplify the math's a little, this can also be re-written as:

Where jω = 2πƒ and the output voltage Vout is a constant 1/RC times the integral of
the input voltage Vin with respect to time. The minus sign (-) indicates an 180o phase
shift because the input signal is connected directly to the inverting input terminal of
the op-amp.

 As a Differentiator

Differentiator is exact opposite to the Integrator, as the position of the capacitor and
resistor have been reversed and now the reactance, Xc is connected to the input
terminal of the inverting amplifier while the resistor, Rf forms the negative feedback
element across the operational amplifier as normal.

This circuit performs the mathematical operation of Differentiation that is it
"PRODUCES A VOLTAGE OUTPUT WHICH IS DIRECTLY PROPORTIONAL TO
THE INPUT VOLTAGE'S RATE-OF-CHANGE WITH RESPECT TO TIME".

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In other words the faster or larger the change to the input voltage signal, the greater
the input current, the greater will be the output voltage change in response,
becoming more of a "spike" in shape.

As with the integrator circuit, we have a resistor and capacitor forming an RC
Network across the operational amplifier and the reactance (XC) of the capacitor
plays a major role in the performance of a Differentiator Amplifier.

Differentiator Amplifier Circuit

The input signal to the differentiator is applied to the capacitor. The capacitor blocks
any DC content so there is no current flow to the amplifier summing point, X resulting
in zero output voltage. The capacitor only allows AC type input voltage changes to
pass through and whose frequency is dependent on the rate of change of the input
signal. At low frequencies the reactance of the capacitor is "High" resulting in a low
gain (Rf/Xc) and low output voltage from the op-amp. At higher frequencies the
reactance of the capacitor is much lower resulting in a higher gain and higher output
voltage from the differentiator amplifier.

However, at high frequencies a differentiator circuit becomes unstable and will start
to oscillate. This is due mainly to the first-order effect, which determines the
frequency response of the op-amp circuit causing a second-order response which, at
high frequencies gives an output voltage far higher than what would be expected. To
avoid this high frequency gain of the circuit needs to be reduced by adding an
additional small value capacitor across the feedback resistor Rf.

Ok, some math's to explain what's going on! Since the node voltage of the

operational amplifier at its inverting input terminal is zero, the current, i flowing
through the capacitor will be given as:

The charge on the capacitor equals Capacitance x Voltage across the capacitor

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The rate of change of this charge is

But dQ/dt is the capacitor current i

From which we have an ideal voltage output for the Differentiator Amplifier is given
as:

Therefore, the output voltage Vout is a constant -Rf.C times the derivative of the
input voltage Vin with respect to time. The minus sign indicates a 180 o phase shift
because the input signal is connected to the inverting input terminal of the
operational amplifier.

One final point to mention, the Differentiator Amplifier circuit in its basic form has two
main disadvantages compared to the previous integrator circuit. One is that it suffers
from instability at high frequencies as mentioned above, and the other is that the
capacitive input makes it very susceptible to random noise signals and any noise or
harmonics present in the source circuit will be amplified more than the input signal
itself. This is because the output is proportional to the slope of the input voltage so
some means of limiting the bandwidth in order to achieve closed-loop stability is
required.

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Differentiator Waveforms

If we apply a constantly changing signal such as a Square-wave, Triangular or Sine-
wave type signal to the input of a differentiator amplifier circuit the resultant output
signal will be changed and whose final shape is dependent upon the RC time
constant of the Resistor/Capacitor combination.

 As an Inverter

The triangular gain block symbol is again used to represent an ideal op amp. The
input terminal, + (Vp), is called the non-inverting input, whereas – (Vn) marks the

inverting input. It is similar to the non-inverting circuit shown in Figure 4 except that

Now the signal is applied to the inverting terminal via R1 and the non-inverting
terminal is grounded.

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An op amp can produce a signal which is 180 degrees out of phase (inverted) with
respect to the input signal. To use an op amp as an inverting amplifier, send the
signal into the negative input instead of the positive input. As the op amp will do
everything it possibly can to make the voltage (signal) on the negative input match
the positive input. In the following diagram, that the positive input is connected to
ground. It's shown as being connected through a resistor but the resistance to
ground in unimportant. What is important is that the positive input has no signal (it's
connected to the reference, ground). This means that the op amp's negative input
will have no visible (voltage) signal on it. When you're driving the negative input it will
act as a virtual ground. The input is converted from a voltage drive to a current drive.
The change in current is what drives the op amp. This is important to know because
at the negative input with an oscilloscope, no signal (when the circuit is an inverting
amplifier). The op amp inputs had very high impedance. While this is true, when
using the inverting input with feedback (which is necessary for audio reproduction),
the input impedance becomes the value of the input resistor.

Calculating Voltage Gain (inverting input):

By knowing the value of the feedback, inverting input resistor and input voltage, we
can calculate the output voltage. The formula is:

Vout = Vin*(Rf/Ri)*-1

Inverting Amplifier Configuration

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In this Inverting Amplifier circuit the operational amplifier is connected with feedback
to produce a closed loop operation. For ideal op-amps there are two very important
rules to remember about inverting amplifiers, these are: "no current flows into the
input terminal" and that "V1 equals V2", (in real op-amps both these rules are
broken). This is because the junction of the input and feedback signal (X) is at the
same potential as the positive (+) input which is at zero volts or ground then, the
junction is a "Virtual Earth". Because of this virtual earth node the input resistance of
the amplifier is equal to the value of the input resistor, Rin and the closed loop gain
of the inverting amplifier can be set by the ratio of the two external resistors.

We said above that there are two very important rules to remember about Inverting
Amplifiers or any operational amplifier for that matter and these are.

1. No Current Flows into the Input Terminals

2. The Differential Input Voltage is Zero as V1 = V2 = 0 (Virtual Earth)

Then by using these two rules we can derive the equation for calculating the closed-
loop gain of an inverting amplifier, using first principles.

Current ( i ) flows through the resistor network as shown.


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Then, the Closed-Loop Voltage Gain of an Inverting Amplifier is given as.

And this can be transposed to give Vout as:


LINEAR OUTPUT

The negative sign in the equation indicates an inversion of the output signal with
respect to the input as it is 180o out of phase. This is due to the feedback being
negative in value.

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The equation for the output voltage Vout also shows that the circuit is linear in nature
for a fixed amplifier gain as Vout = Vin x Gain. This property can be very useful for
converting a smaller sensor signal to a much larger voltage.

 As a Comparator

The operational amplifier was originally developed for analogue computing (our PCs
are digital computers) and when introduced were complex and expensive
components. Now they are in integrated circuit form and are very cheap, about 50 p
(0.7 Euros). They are not very spectacular, but are extremely useful.

A comparator compares two input voltages. These are usually a reference voltage
and a signal from a sensor. The output switches state when the signal input crosses
the reference voltage.

THE COMPARATOR RELIES ON THE VERY HIGH OPEN LOOP GAIN OF THE
OP' AMP'. VERY SMALL CHANGES IN THE INPUT CAUSE THE OP AMP TO
SATURATE SO THE OUTPUT IS ALWAYS LOW OR HIGH AND ALMOST NEVER
UNDECIDED.
For a real-life op' amp' this gain will be between 105 and 107.
This means that a potential difference between V1 and V2 of only a few micro volts is
sufficient to saturate the op' amp'.

If V1 is greater than V2 then Vout will go high (close to the + supply voltage)
If V1 is less than V2 then Vout will go low (close to the - supply voltage).


Operational amplifiers require a dual power supply, which means having a central 0
volts rail, and a + 15 V rail and a – 15 V rail. The full circuit diagram is shown below,
but generally we will ignore the power supply.

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Notice that the op-amp has two inputs and one output. It amplifies the difference
between the inverting input and non-inverting input. Be careful not to confuse the
symbol with a non-inverting gate.

Overview of the uA741
Of the different types of op – amps produced, type 741 has achieved a very wide
popularity. It is available in 14- pin dual-in line, 8 – pin dual-in line or in TO- style
packages. Integrated circuit type 747 accommodates two type 741 operational
amplifiers in a single package.

uA 741 various package styles:


Definition of 741-pin functions:

1. Pin 1 (Offset Null): 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 offset. 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.

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2. 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 cannot do its work.
3. Pin 3 (Non-Inverted Input): All input signals at this pin will be processed
normally without inversion. The rest is the same as pin 2.
4. 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).
5. Pin 5 (Offset Null): See pin 1
6. Pin 6 (Output): Output signal's polarity will be the opposite 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.
7. 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.
8. 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.


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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 response 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.

Given Task:
We are given to desing an operational amplifier having following specifications such
as:

All the circuits’ i.e. operational amplifier as an integrator, an inverter, a differentiator,
and as a comparator should …

a) Use single IC 741 for all the 4 circuits
b) Use switches to ON just one single at a time
c) Single input supply

Problems and their solutions
Some of the problems we faced during our project are listed below:

I. Complexity of the practically design circuit
II. Compiling of a circuit
III. Use of the switches
IV. Isolation the input supply

We have overcome on these problems as:
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 Complexity of the practically design circuits:

Ideally the all the circuits are grounded at the non-inverting terminal (03) but
practically we use respective resistances across it to avoid… that makes the circuit
complex

Solution:

To make the circuit practically efficient it is recommended to use these resistances
rather than being it grounded

 Compiling of the circuit:

To achieve the task, all the circuits should be complied up on a single overboard
using IC.

Solution:

For this we design circuit by our self shown below:


Circuit design by the Group Members

BS.(Hons.) 4th Semester

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 Use switches:

We are assigned to use switches to ON the one circuit at a time

Solution:

We use switches separately for all the circuits at inverting terminal (02) , as the input
is supplied to all circuit through inverting terminal, than by the help of the switches
we allowed input signal to pass through a selected portion of the circuit

Circuit design by the Group Members

BS.(Hons.) 4th Semester

 Isolation of the circuit:

Input supply can isolated

Solution:

For this we have to use some of the extra switches at the input supply to the
inverting terminal that isolates the input supply.

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Future Directions:
To get more efficient result w can alter the following specifications as:

1. We can use less switches up to just 4 If we does not isolates the input supply
2. For avoid any damage to the LED we can use another resistance at the
output terminal of almost 1K.
3. We can use more practically effiecnt circuits design.


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References

1) www.amplifiercircuits.com ………………………………..26-05-11
2) www.antonnie-education.co.edu ..………………………15-06-11
3) www.bcae1.com.……………………….…………………..14-06-11
4) www.brown.edu …………………………………………...14-06-11
5) www.bucknell.edu ………..…………………………….....14-06-11
6) www.circuitstoday.com ……………………………………15-06-11
7) www.electronicstutorial.com ……………………………..14-06-11
8) www.forumer.com …………….……….…………………..14-06-11
9) www.hamradioindia.com …………….……………………15-06-11
10) Handbook of Operational amplifier applications by Thomas R
.Brown J………………………………..………………...…31-05-11
11) www.hyperphyscis.com ……………..……………………14-06-11
12) Mixed signal and analogue operational amplifier by Jim
Karki(1988)………………………………………………….31-05-11
13) www.sentex.net ……………………………………………15-06-11
14) www.softwarefrodeucation.com ………………………….14-06-11
15) www.swarthmore.edu ……………….…………………….14-06-11


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