TDS684B noise measurment. Is this normal?

[Jwalling]

Hello all,

I've attached a picture of a TDS684B and a TDS7054 with their inputs set to 50 Ohms 1VDC per division and coupling set to GND. The measurement is set for Pk-Pk amplitude. The measurement shows 160mV of noise. I've tried the test on a TDS684C as well and all seem to show roughly the same amount of noise. Is this normal?
I suspect there's a good reason for this, and would be very interested in knowing why.
Thanks!

Jay

[T3sl4co1l]

What's the bandwidth?

Looks like normal noise of the internal preamp / driver / ADC.  Knock it down to a lower bandwidth setting (or turn on averaging) and it should decrease accordingly.

The scale of the "signal" doesn't matter, because it's a few counts at the ADC, not actually a few volts at the input.

For further reading, check out the user manual in great detail (it should specify what the noise floor and bandwidth is on various ranges), and read up on theory like the Shannon "noisy channel" theorem, Johnson-Nyquist noise, and etc.

Tim

[tszaboo]

The scope has 8 bit resolution, than you have ~10 LSB noise. I think it is good for a Tektronics. Probably they have their usual overclocked ADCs and lowest cost analog front end before it.

[rf-loop]

Looks normal.

http://cp.literature.agilent.com/litweb/pdf/5989-3020EN.pdf

[Jwalling]

Looks normal.

http://cp.literature.agilent.com/litweb/pdf/5989-3020EN.pdf

Excellent doc! Thank you for that, and thanks to all who took the time to reply.

Jay

[tautech]

Further info:
http://www.eevblog.com/2014/04/10/eevblog-601-why-digital-oscilloscopes-appear-noisy/
http://www.eevblog.com/2014/04/27/eevblog-610-why-digital-scopes-appear-noisy-part-2/