Behavior of oscilliscope software bandwidth limiters

[GlowingGhoul]

Do scopes that have software upgradeable bandwidth exhibit the typical 3db dropoff at the artificial maximum bandwidth? It would seem like the designers would have to out of their way to make that happen when the actual front end has a bandwidth significantly higher than the software limited bandwidth, but maybe they do?

[Fungus]

The DS1054Z has a switchable capacitor on the front end to reduce the bandwidth, it's not software on that particular scope.



So yes, it will have a fairly standard rolloff.

[GlowingGhoul]

The DS1054Z has a switchable capacitor on the front end to reduce the bandwidth, it's not software on that particular scope.



So yes, it will have a fairly standard rolloff.

Do Tek and Keysight use a similar technique for bandwidth limiters? Seems like something that wouldn't require hardware to accomplish really...

[Fungus]

Do Tek and Keysight use a similar technique for bandwidth limiters? Seems like something that wouldn't require hardware to accomplish really...

I'm sure people will let us know :-)

It's really cheap to do in hardware (one capacitor+one transistor). Doing it in analog hardware probably gives a nicer result, too.

So ... even though it's not necessary, I'd be willing to bet they do it in hardware.

[Wuerstchenhund]

Do Tek and Keysight use a similar technique for bandwidth limiters? Seems like something that wouldn't require hardware to accomplish really...

Yes, the big brands (Keysight, LeCroy, Tek, R&S) use a similar approach (hardware filters).

It's also simpler to do in hardware than in software, because you can't just tell the scope "ignore any signal about XXX MHz". You would have to filter out signal components over the desired cutoff frequency, which usually means you have to employ FFT which is pretty compute-intensive and would slow down your scope a lot.

[Howardlong]

This might be worth a read http://literature.cdn.keysight.com/litweb/pdf/5989-5733EN.pdf?cmpid=zzfindevaluatingbandwidth

[Fungus]

You would have to filter out signal components over the desired cutoff frequency, which usually means you have to employ FFT which is pretty compute-intensive and would slow down your scope a lot.

It would also distort the signal slightly - not good in a device like an oscilloscope.

[tautech]

Do scopes that have software upgradeable bandwidth exhibit the typical 3db dropoff at the artificial maximum bandwidth?

No, not AFAIK.