An instrumentation amplifier is a type of integrated circuit, primarily used for amplifying the signal. It is part of the differential amplifier family because it increases the disparity between two inputs. The main function of an Instrumentation amplifier is to reduce the noise produced by the machines or circuits. Every IC pin has the ability to reject noise, which is known as the CMRR (common-mode rejection ratio). Because of its characteristics such as high CMRR, high open-loop gain, low drift, and low DC offset, the instrumentation amplifier IC is an essential component in the design of the circuit.
What is an instrumentation amplifier?
An instrumentation amplifier amplifies very low-level signals while rejecting noise and interference. Heartbeats, blood pressure, temperature, earthquakes, and so on are all examples. As a result, the following are the essential characteristics of a good instrumentation amplifier:
- The instrumentation amplifiers' inputs will have very low signal energy. As a result, the instrumentation amplifier must have a high gain and be accurate.
- The gain should be simple to adjust with a single control.
- To avoid loading, it must have a high input impedance and a low output impedance.
- Because common mode signals, such as noise, are typically present in transducer output when transmitted over long wires, the instrumentation amplifier should have a high CMRR.
- It must also have a high slew rate to handle events with sharp rise times and provide the most undistorted output voltage swing.
Op-Amp and the Instrumentation amplifier
The op-amp instrumentation amplifier circuit is depicted below. The first and second op-amps are non-inverting amplifiers, and the third op-amp is a difference amplifier. Together, these three op-amps create an instrumentation amplifier. The ultimate output Vout of an instrumentation amplifier is the amplified difference of the input signals applied to the input terminals of op-amp 3. Let Vo1 and Vo2 be the outputs of op-amps 1 and 2, respectively.
then, Vout = (R3/R2) (Vo1-Vo2)
Examine the instrumentation amplifier's input stage, as depicted in the image below. The derivation of an instrumentation amplifier is explained more below. The input voltage V1 is represented by the potential at node A. As a result of the virtual short idea, the potential at node B is also V1. As a result, the potential at node G is also V1.
The input voltage V2 is represented by the potential at node D. As a result of the virtual short, the potential at node C is also V2. As a result, the potential at node H is also V2.
The instrumentation amplifier operates as follows: ideally, the current to the input stage op-amps is zero. As a result, the current I across resistors R1, Rgain, and R1 remains constant.
Using Ohm's law to connect nodes E and F,
I = (Vo1-Vo2)/(R1+Rgain+R1) ……………………….(1)
I = (Vo1-Vo2)/(2R1+Rgain)
Because no current is flowing to the inputs of op-amps 1 and 2, the current I between nodes G and H can be calculated as follows:
I = (VG-VH) / Rgain = (V1-V2) / Rgain........................... (2)
Putting equations 1 and 2 together
(Vo1-Vo2)/2R1+Rgain = (V1-V2)/Rgain
(Vo1-Vo2) = (2R1+Rgain)(V1-V2)/Rgain........................... (3)
The difference amplifier's output is provided as,
(R3/R2) Vout (Vo1-Vo2)
As a result, (Vo1 - Vo2) = (R2/R3)Vout
By substituting (Vo1 - Vo2) in equation 3, we obtain
(2R1+Rgain)(V1-V2)/Rgain = (R2/R3)Vout
Specifically, Vout = (R3/R2)(2R1+Rgain)/Rgain (V1-V2)
The output voltage of an instrumentation amplifier is given by the equation above.
The term (R3/R2)(2R1+Rgain)/Rgain represents the amplifier's overall gain.
The value of resistor Rgain can be used to alter the overall voltage gain of an instrumentation amplifier. The difference amplifier provides common mode signal attenuation for the instrumentation amplifier.
Top 10 Lab Automation Companies In The World By The Revenue
Benefits of Instrumentation Amplifier
The following are some of the benefits of an instrumentation amplifier.
- A three-op-amp instrumentation amplifier circuit's gain can be easily changed by modifying the value of only one resistor Rgain.
- The amplifier's gain is solely determined by the external resistors utilized.
- Because of the emitter follower configurations of amplifiers 1 and 2, the input impedance is extremely high.
- Because of the difference amplifier3, the instrumentation amplifier's output impedance is extremely low.
- The CMRR of op-amp 3 is extremely high, and nearly all of the common mode signal is rejected.
Applications of Instrumentation Amplifier
The instrumentation amplifier's applications include the following.
- These amplifiers are used mostly in situations where high differential gain accuracy is required, strength must be maintained in noisy environments, and large common-mode signals exist. Some of the applications are as follows:
- Instrumentation amplifiers are used to acquire data from small o/p transducers such as thermocouples, strain gauges, Wheatstone bridge measurements, and so on.
- These amplifiers are utilized in navigation, medical, radar, and other applications.
- These amplifiers are used to improve the S/N ratio (signal to noise) in audio applications such as low-amplitude audio streams.
- These amplifiers are utilized in the conditioning of high-speed signals for image and video data gathering.
- These amplifiers are used in RF cable systems to boost high-frequency signals.
Difference between instrumentation amplifier and operational amplifier
The following are the primary distinctions between operational amplifiers and instrumentation amplifiers.
- One type of integrated circuit is an operational amplifier (op-amp).
- One sort of differential amplifier is the instrumentation amplifier.
- Three operational amplifiers can be used to construct an instrumentation amplifier.
- A single operational amplifier can be used to build the differential amplifier.
- The mismatched resistors have an effect on the output voltage of the difference amplifier.
- Instrumentation amplifiers provide gain with a single resistor in their primary phase, eliminating the necessity for resistor matching.