Explain the concept of operational amplifier (op-amp) common-mode rejection ratio (CMRR).
1 Answer
An operational amplifier, often referred to as an op-amp, is a fundamental electronic component widely used in various circuits for amplifying and processing analog signals. One important characteristic of op-amps is their ability to reject common-mode signals, which gives rise to the concept of Common-Mode Rejection Ratio (CMRR).
Common-mode signals are those that appear simultaneously and with the same magnitude on both the inverting and non-inverting inputs of an op-amp. Ideally, an op-amp should amplify only the difference between the voltages applied to its inputs (differential input), completely ignoring any common-mode voltage. However, due to imperfections and non-idealities in real-world op-amp circuits, some amount of common-mode voltage might get inadvertently amplified.
CMRR is a measure of how effectively an op-amp can reject or attenuate these common-mode signals and focus only on the desired differential input. It is defined as the ratio of the gain for the differential input to the gain for the common-mode input, both expressed in decibels (dB). Mathematically, CMRR can be expressed as:
CMRR
=
20
log
10
(
Differential Gain
Common-Mode Gain
)
CMRR=20log
10
(
Common-Mode Gain
Differential Gain
)
In this equation, the "Differential Gain" refers to the amplification an op-amp provides to the actual difference in voltage between its inverting and non-inverting inputs, while the "Common-Mode Gain" represents the amplification of any voltage that is present in equal magnitude on both inputs.
A higher CMRR value indicates better rejection of common-mode signals, and therefore, a higher degree of accuracy in amplifying only the intended differential input. CMRR is typically expressed in decibels (dB), a logarithmic unit that allows for easy comparison of signal levels.
It's important to note that achieving a high CMRR is crucial in applications where the desired signal is much smaller than any common-mode interference or noise. Engineers and designers often select op-amps with higher CMRR values for precision applications to minimize the impact of unwanted signals and improve the overall accuracy of the circuit.
Common-mode signals are those that appear simultaneously and with the same magnitude on both the inverting and non-inverting inputs of an op-amp. Ideally, an op-amp should amplify only the difference between the voltages applied to its inputs (differential input), completely ignoring any common-mode voltage. However, due to imperfections and non-idealities in real-world op-amp circuits, some amount of common-mode voltage might get inadvertently amplified.
CMRR is a measure of how effectively an op-amp can reject or attenuate these common-mode signals and focus only on the desired differential input. It is defined as the ratio of the gain for the differential input to the gain for the common-mode input, both expressed in decibels (dB). Mathematically, CMRR can be expressed as:
CMRR
=
20
log
10
(
Differential Gain
Common-Mode Gain
)
CMRR=20log
10
(
Common-Mode Gain
Differential Gain
)
In this equation, the "Differential Gain" refers to the amplification an op-amp provides to the actual difference in voltage between its inverting and non-inverting inputs, while the "Common-Mode Gain" represents the amplification of any voltage that is present in equal magnitude on both inputs.
A higher CMRR value indicates better rejection of common-mode signals, and therefore, a higher degree of accuracy in amplifying only the intended differential input. CMRR is typically expressed in decibels (dB), a logarithmic unit that allows for easy comparison of signal levels.
It's important to note that achieving a high CMRR is crucial in applications where the desired signal is much smaller than any common-mode interference or noise. Engineers and designers often select op-amps with higher CMRR values for precision applications to minimize the impact of unwanted signals and improve the overall accuracy of the circuit.