1. OP-AMP PARAMETERS
EXPERIMENT NO 5
Batch B1 Bock 1
Omkar Rane SETB118
Rohit Mane SETB102
Abhishek Sainkar SETB104
Tanmay Kale SETB112
AUGUST 8, 2017
MIT ACADEMY OF ENGINEERING, DEPARTMENT ENTC ENGG
ANALOG ELECTRONICS
2. S.Y.B. Tech(AE): 2017-18 Analog Electronics
EXPERIMENT No: 5
OP-AMP parameters
Fig. 1 Opamp Parameters
Offset Voltage:
A practical concern for op-amp performance is voltage offset. That is, effect of
having the output voltage something other than zero volts when the two input
terminals are shorted together. Remember that operational amplifiers are
differential amplifiers above all: they're supposed to amplify the difference in voltage
between the two input connections and nothing more.
Difference is exactly zero volts, we would (ideally) expect to have exactly zero volts
present on the output. However, in the real world this rarely happens. Even if the
op-amp in question has zero common-mode gain, the output voltage may not be at
zero when both inputs are shorted together.
This deviation from zero is called offset.A perfect op-amp would output exactly zero
volts with both its inputs shorted together and grounded. However, most op-amps
off the shelf will drive their outputs to a saturated level, either negative or positive.
Offset voltage will tend to introduce slight errorsin any op-amp circuit. So how do
we compensate for it? There are usually provisions made by the manufacturer to
trim the offset of a packaged op amp.
Usually, two extra terminals on the op-amp package are reserved for connecting an
external trim" potentiometer. These connection points are labeled offset null.
OP-Amp parameters FOR HIGH SPEED
operation & HIGH PERFORMANCE efficiency
Inputoffset
voltage
Inputbias
/offsetcurrent
Slew Rate CMRR
3. S.Y.B. Tech(AE): 2017-18 Analog Electronics
Fig. 2 Input offset voltage
Bias and Offset current:
Inputs on an op-amp have extremely high input impedances. That is, the input
currents entering or exiting an op-amp's two input signal connections are extremely
small. For most purposes of op-amp circuit analysis, we treat themas though they
don't exist at all.We analyze the circuit as though there wasabsolutely zero current
entering or exiting the input connections.
This idyllic picture, however, is not entirely true. Op-amps, especially those op-
amps with bipolar transistor inputs, have to have some amount of current through
their input connections in order for their internal circuits to be properly biased.
These currents, logically, are called bias currents.
The input bias current is the dc current required to properly operate the first stage
within the op-amp. The input impedance is another. Also, the input offset current
which can become a problem if both dc input currents are not the same.
Fig.3 Input bias current
The input offset current Ios, is the difference of the input bias currents,expressed
as an absolute value
Slew Rate
4. S.Y.B. Tech(AE): 2017-18 Analog Electronics
Slew rate is defined as the maximum rate of change of the output voltage under
large signal conditions. Expressed in units of volts per microsecond (V/us), the
slew rate is dependent on the frequency response of the internal stages of the
op-amp. Thus, the higher the slew rate, the better the frequency response of the
amplifier. The measurement of the operational amplifier’s slew rate is always
accomplished with a larger-signal amplifier having unity gain with a high-input
frequency signal. 𝑆𝑙𝑒𝑤 𝑅𝑎𝑡𝑒 =
∆𝑉𝑜𝑢𝑡
∆𝑡
(𝑣 𝜇𝑠⁄ )
Fig.4 Slew rate Measurement
CMRR
If the same signal is applied simultaneouslyto both inputs, called the common-
mode input, then the output voltage of an ideal op-amp should be zero. Since
operational amplifiers are not ideal devices, a small but finite output voltage will
be present whenboth the input voltages are the same. The ratio of the common-
mode input voltage to the generated output voltage is termed as common-mode
rejection ratio (CMRR) and is expressed in decibels. The higher the CMRR is the
better for the rejection and the smaller for the output voltage.
𝐶𝑀𝑅𝑅 = 20𝑙𝑜𝑔
𝐴𝑣(𝑑)
𝐴𝑣(𝑐𝑚)
(𝑑𝐵)
Fig.5CMRR Measurement
Pre Lab activity:
5. S.Y.B. Tech(AE): 2017-18 Analog Electronics
1. In Fig.2 Prove that
1
1
R
R
V
Vio
f
O
V1=V2=Vio
Vs=R1*Vio/(Rf + R1) – voltage divider rule
Avf= Vo/Vio=(Rf+R1)/R1= 1+Rf/R1
Vio=Vo/(1+Rf/R1)
2. Following is the circuit used for bias current measurement
Fig 6 Circuits to measure input bias currents Ib1 and Ib2, respectively.
a. Write the formula for Ib1 =V1/R1
b. Write the formula for Ib2=V2/R2
Lab Exercise: -
1. Circuit diagram of Offset voltage, bias and offset current, CMRR and Slew
rate measurement
2. Procedure: - (Write in your own words)
1) Use multisim software to draw various configuration of op amps.
2) The various op amp parameters are verified through various
configurations you have build that on multisim to calculate
theoretical and practical values.
3) Use various formula to figure out following parameters:
Ib1=V1/R1,
6. S.Y.B. Tech(AE): 2017-18 Analog Electronics
Ib2=V2/R2
A=Rf/Ri
Ib=(Ib1+Ib2)/2
Iios=|Ib1-Ib2|
Vid= Vi1-Vi2
Vod=Vid* A
CMRR= Ad/Ac
3. List the Equipment / Component required for the experiment
Equipment / Components Specifications/Values
Function Generator CADDO,4061,3MHz Pulse
Generator with 40 MHz Frequency
Counter
CRO HAL-TEC plus, HT4030,30MHz,
Oscilloscope
Resistor R= 1MΩ, 100kΩ, 10kΩ
Breadboard, wires
Variable Power Supply
Operational amplifier IC 741
Capacitor 0.1 farad, 0.01 farads ceramic
type
MULTISIM 12 0r 8
4. Observation Table (Multisim readings)
Parameters Practical
Datasheet
specifications
7. S.Y.B. Tech(AE): 2017-18 Analog Electronics
Input offset voltage 0.2 mV 1 mV
Voltage gain Av 10 2*105
Input bias current 14 mA 50 nA
Input resistance ∞ 2 MΩ
Output resistance 0 75 Ω
Input offset current 10 mA 20 nA
Slew rate ∞ 0.5 V/µsec
CMRR 58 dB 80 dB
Conclusion: -
We had studied various op amp parameters like slew rate, input bias current, input offset
current, input offset voltage, open loop gain. we had verified these parameters through
various op amps configuration.
Post Lab. Activity: -
1. List out parameters of Opamp OP07
8. S.Y.B. Tech(AE): 2017-18 Analog Electronics
2. What is the highest frequency of a triangle wave of 20-V peak-to-peak
amplitude that can be reproduced by an op amp whose slew rate is 10V/μs?
For a sine wave of the same frequency what is the maximum amplitude of
output signal that remain undistorted?
Answer:
Given : -
Slew Rate = 10V/μs2
VP-P = 20 volts
Solution: Type equation here.
Slew Rate = 2πf VP-P
10V/μs= 2πf 20
f =79 kHz
Now, Vp-p = Slew rate/2πf
= 10 / 2π(79kHz)
= 2.0146 x 10-5
Note :- Kindly attach screenshot of your performed experiments
Videos on OP -AMP Parameter:
https://youtu.be/TxBJb-Z0XFI
https://youtu.be/hq6e9v1ZYG4
