What is GBW (Gain Bandwidth)?
The gain bandwidth (GBW) of OPERATIONAL AMPLIFIERS is an important performance index that determines the signal frequency band that OPERATIONAL AMPLIFIERS can handle.
OPERATIONAL AMPLIFIERS with a large GBW are suitable for high frequency signal processing.
Designers must select OPERATIONAL AMPLIFIERS based on the frequency band and GBW required for signal processing.
Definition of GBW
Definition formula: GBW = Open loop gain × Frequency
The open-loop gain frequency characteristics of OPERATIONAL AMPLIFIERS are shown in the figure below.
What is -20dB/decade?
-20dB/decade refers to the slope where the open loop gain becomes 1/10 (-20dB) when the frequency increases by 10 times, and GBW is expressed as the product of the open loop gain and frequency in the frequency band that maintains this slope.
In this frequency band, the following equation is always satisfied:
Relationship between GBW and error
In "Basic Operation OPERATIONAL AMPLIFIERS," we explained that the closed-loop gain of an inverting amplifier can be determined by the ratio of resistors, under the assumption that an imaginary short exists.
We also explained that an imaginary short occurs when the open-loop gain is sufficiently large.
The criteria for determining whether an imaginary short can be considered equivalent depends on the expected signal bandwidth and the closed-loop gain error of the inverting amplifier required by the system.
If the required error cannot be met, you will need to change to OPERATIONAL AMPLIFIERS with a larger GBW.
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