ADC used in SDG6052X for external modulation input - Page 1
Forum section: electronics / testgear

author: suspension
author_rank: Regular Contributor
timestamp: October 20, 2024, 04:40:59 am
content: HelloI was wondering if some one have any information on the ADC used in SDG6052X waveform generator to convert the external input signal to digital before used for modulation.ThanksS

author: TurboTom
author_rank: Super Contributor
timestamp: October 20, 2024, 07:36:32 am
content: Since I didn't find a dedicated ADC chip on the SDG6000X mainboard when I tore my instrument down for some "maintenance", I assume that Siglent utilizes one of the "XADC" 12bit 1MSa/s units integral to the ZYNQ 7000 on the CPU module for the modulation input. This may also explain the relative lack of auxiliary I/O, considering the second XADC unit may be required for internal "housekeeping".

author: suspension
author_rank: Regular Contributor
timestamp: October 20, 2024, 08:05:33 am
content: Thank you for the information. This probably is the reason. Their external modulation signal is also maxed at 40KHz I think.Are you sure the FPGA was Zynq? I always though it to be either Artix7 or Kintex 7. Just curious.

author: TurboTom
author_rank: Super Contributor
timestamp: October 20, 2024, 09:28:27 am
content: The Zynq is the SoC that controls the U/I and all the arbitraries handling and is located on the SIMM-style CPU module under the little heat sink. The Kintex-7 is the FPGA used as the sampling engine, responsible for the data "assembly" / transfer to the DAC. Unfortunately, Siglent "economized" the dedicated sample RAM at the Kintex so the SoC has to do all the arbitraries handling, but apparently, it does the job as per spec.I just did some testing myself and found that the external modulation input is sampled approx. every 1.8µs, and some low-pass filtering is also taking place. I attached a screenshot of a 10MHz square wave, amplitude modulated by a 100kHz square wave via the external input. An exact evaluation of the resolution of the modulation input is difficult due to the noise, but I got the impression that at increments of 3...4mV (tested with a DC "modulation" signal close to the cut-off point at -5.8xx V), the modulated output amplitude changes more than "in between", so this would make a resolution of 12 bit at least plausible. For all practical applications (checked with FM/frequency jitter), the modulation input can be considered to act "analog-like" with no noticeable increments due to the noise (S/N approx 35dB).It's a shame the SDG6000X hasn't got more connectivity, a separate sync output would make life so much easier when trying to sync on the signal buried in the noise close to the cut-off point... But many other manufacturers also don't provide this luxuryand one has to dig a lot deeper into the wallet to find a current AWG with these features.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: October 20, 2024, 10:20:24 am
content: When I was looking for a function generator with wide modulation capabilities, I came across Aim-TTI TGF4000 series, which has a 5 MHz bandwidth for external modulation input. That seems to be better than most others.Another problem with virtually all such arbitrary function generators is that they can do only one type of modulation at a time. So I ended up getting HP 8780A, discussed recently in another thread.

author: suspension
author_rank: Regular Contributor
timestamp: October 22, 2024, 04:26:30 pm
content: Thanks for taking time to do this test!I see that the DDR RAM they used to store wave samples is now gone? I wonder how many sample points this equipment support. For me it looks like all samples are stored in Kintex block RAM.