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Topic: Op Amp GBWP (Read 219 times) previous topic - next topic

navab1362

Hello
What's the of op amp gbwp and whats the meaning of higher and lower bandwidth?
Excuse me for elementary questions

Grumpy_Mike

If the GBWP ( Gain Bandwidth Product ) of an operational amplifier is 1 MHz, it means that the gain of the device falls to unity at 1 MHz. Hence, when the device is wired for unity gain, it will work up to 1 MHz (GBWP = gain × bandwidth, therefore if BW = 1 MHz, then gain = 1) without excessively distorting the signal.

Bandwidth is the frequency range. High means a large range of frequency lower means less. When the gain falls below one it is no longer able to amplify.

MarkT

#2
Oct 21, 2017, 12:45 pm Last Edit: Oct 21, 2017, 12:46 pm by MarkT
And all opamps have a gain that falls off with frequency such that the product of gain and bandwidth is
basically constant from a few tens of Hz upto MHz (if the device goes that high).  This is a consequence
of the amplifier having to be stable in a closed-loop feedback setup.

If you want accurate low distortion behaviour from an opamp you want to stay well below the
gain-bw product.

This is one of the reasons its recommended to limit each opamp to a low gain of 10 to 20 and
string several together for higher gain.  A single stage with gain 1000x has about 100 less bandwidth
than 3 linked 10x stages (this can be a show-stopper if you're not expecting it!)

The exception to this is instrumentation amplifiers (like strain-guage and thermocouple amps) where single
stages with high gain are common - but the bandwidth requirements are very modest.

For audio use you'd want a bandwidth of 20kHz typically, meaning a gain-bw product of several MHz is
needed.   For an opamp before an ADC sampling at 1kSPS, a lower gain-bw product of 100kHz would
likely be enough.

Another specification useful for bandwidth calculations is the output slew-rate, this limits the dV/dt
at the output, and affects gain at high output amplitude independently of the gain-bw product.
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