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Cheap and Small Dynamic Signal Analyzer?
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TopQuark:

--- Quote from: trampas on October 26, 2022, 12:21:39 am ---I was looking for something like the DSA that can measure amplifier noise floor and was wondering what options are out there?

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I was thinking the same. Couldn't find anything I like in the market, so I decided to roll my own. I ordered a AD4630-24 eval board (back ordered till late Nov unfortunately) to pair it with a beefy Zynq ultrascale dev board I already have, so the hardware should be plug n play.

It will take the AD4630-24 32.768ms to collect 65536 samples at 2 MSPS. Vivado estimates the zynq chip can do 2 channel, 30 bit input, 65536 bin FFT in roughly 1.5ms, so it should be no problem at all to have 32768 lines FFT resolution and 1MHz real time bandwidth. The AD4630-24 has 105.7 dB typical dynamic range as stated in the datesheet.

For context, the SRS785 cost 14k USD, can only do 800 line FFT, 102.4 kHz real time bandwidth, 90 dB typical FFT dynamic range. The zynq dev board I have cost around 1k USD (massively overkill for the job), and the AD4630-24 eval board is 200 USD. All in all, the cobbled together solution should beat the pants off the SRS785.

Of course, talk is cheap, and I haven't written a single line of code for the project yet, so don't have your hopes set high for now  ::)



Berni:

--- Quote from: trampas on October 26, 2022, 12:21:39 am ---I was looking for something like the DSA that can measure amplifier noise floor and was wondering what options are out there?

--- End quote ---

For just noise measurement you can get away with a preamplifier going into an oscilloscope. Mainly because you don't need a lot of dynamic range for this, just high enugh sensitivity.

There are 1000x gain preamplifiers out there from Stanford, but you can just as easily build your own using low noise opamps.

As for measuring the noise of an opamp itself you just build a high gain amplifier circuit out of the opamp you want to test and it will amplify up its own noise to a point where it is easily measurable.



--- Quote from: TopQuark on October 26, 2022, 01:18:49 am ---I was thinking the same. Couldn't find anything I like in the market, so I decided to roll my own. I ordered a AD4630-24 eval board (back ordered till late Nov unfortunately) to pair it with a beefy Zynq ultrascale dev board I already have, so the hardware should be plug n play.

--- End quote ---

That ADC does look like it could make a nice "NanoDSA" when paired up with a fast MCU with hardware floating point. Don't think you quite need the power of an FPGA to do FFTs that fast.

Tho the chip is out of stock everywhere as per chip shortage apocalypse.
TopQuark:

--- Quote ---That ADC does look like it could make a nice "NanoDSA" when paired up with a fast MCU with hardware floating point. Don't think you quite need the power of an FPGA to do FFTs that fast.
--- End quote ---

Yea you can probably get away with a fast MCU like a STM32H7 or something similar. Though once you add in windowing, digital anti aliasing filtering, network analysis, averaging, digital mixing etc. I think it will be a pain to maintain real time analysis capability with a MCU. Perhaps a happy medium would be a cheap Chinese FPGA (e.g. the ones in sipeed tang boards) paired with a decent MCU.

To be honest, the main motivation for wanting to use a overkill zynq ultrascale dev board is because the ADC eval board has a pain in the butt FMC connector, and the FPGA dev board just so happens to support that connector  ::).
Messtechniker:
ESI Juli@—www.esi-audio.com
Sound Blaster X-Fi—www.creative.com
EMU 1212, 0202, 0404—www.emu.com
Lynx L2, L22—www.lynxstudio.com
Asus Xonar Essence—www.asus.com

M-Audio Audiophile 192—www.m-audio.com
(The one I use, no longer available. Note: is PCI,not PCIe)

These have no reconstruction filters which stop an 20kHz regardless of sample rate.
Some may only be available used....

TopQuark:

--- Quote from: maxwell3e10 on August 19, 2020, 03:41:34 am ---AD4003 ADC and OPA828 input amplifier. Anyone has better suggestions?

--- End quote ---

Another option would be AD7768-1, seems purpose made for the job, in stock and not that expensive. I might get a few to play around with.
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