DDS vs TrueArb, something is wrong? or DDS is no go for timing sensitive signal - Page 1
Forum section: electronics / testgear

author: RoadRunner
author_rank: Frequent Contributor
timestamp: May 07, 2017, 08:05:42 pm
content: I was trying to generate UART signal with only 1200 Baud. i have used Siglent easywave software with my SDG2000X to genrate a UART packet with around 5M points in DDS mode at first , and i found out the signal high low timing is just no consistent though the signal. Then i change it to TrueArb mode and everything was just fine.whole packet transmission is "almost" same in both case , it just individual bits which does not seems be following the timings .a document from keysight provide a descent reference to compere between DDS and truearb.http://literature.cdn.keysight.com/litweb/pdf/M8190-91050.pdfPlease take a look at attached images.

author: awallin
author_rank: Frequent Contributor
timestamp: May 08, 2017, 05:08:12 am
content: If the DDS produces an analog sine-wave which then goes through a sine-to-square converter to get your output, then you can expect problems at low frequencies (you mention 1200 baud) because the slew-rate of the sine at zero-crossing is low.I would guess the DDS is more meant for generating sine-wave, where changes in frequency or amplitude can be done fast but perhaps not every cycle.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 08, 2017, 05:21:36 am
content: Might be worth checking to make sure the latest firmware is installed:http://www.siglentamerica.com/gjjrj.aspx?id=15FWIW....Siglent's 2.01.01.23R3 firmware dated 2017/3/23 says:6. Fixed some bugs a) Arb Waveforms In DDS Mode Have One (Small) Glitch Per Cycle; some other items reference ARBsSiglent's 2.01.01.22R5 firmware dated 2016/9/30 says:2. d) Frequency Coupling/Phase Lock Does Not Work in TrueArb; some other items reference DDS and ARBs

author: RoadRunner
author_rank: Frequent Contributor
timestamp: May 08, 2017, 09:30:00 am
content: Quote from: Electro Fan on May 08, 2017, 05:21:36 amWill try to update firmware and see if this makes any difference.

author: pascal_sweden
author_rank: Super Contributor
timestamp: May 08, 2017, 09:36:17 am
content: Just out of interest: Why are you using an AWG/DDS for generating a UART signal?Why don't you use a cheap microcontroller and a 4x4 keypad to generate 16 different test sequences by the push of a button?

author: RoadRunner
author_rank: Frequent Contributor
timestamp: May 08, 2017, 12:20:45 pm
content: Quote from: pascal_sweden on May 08, 2017, 09:36:17 amthough no particular reason . I was just playing around.I was initially using USB to serial converter but , i need to test how my receiver will behave when a noisy and "little" off baud rate signal is being fed into. i was already using my function gen Ch1 . so i just simply used CH2 for UART, i was lasy enough not to use MCU.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 08, 2017, 04:44:15 pm
content: Quote from: Gaurav on May 08, 2017, 09:30:00 amJust a heads-up; probably should read/investigate/consider this before updating the firmware:https://www.eevblog.com/forum/testgear/the-siglent-sdg2042x-thread/msg1203573/#msg1203573

author: RoadRunner
author_rank: Frequent Contributor
timestamp: May 08, 2017, 07:16:16 pm
content: Quote from: Electro Fan on May 08, 2017, 04:44:15 pmoops ,i think for now , i am okey with TrueArb mode .its better to wait a little if this problem associated with R23 version of firmware is wide spread.

author: tautech
author_rank: Super Contributor
timestamp: May 08, 2017, 09:17:58 pm
content: Hard to know what went wrong with Wolf's unit.We've PM'ed about it and maybe it needed another restart after updating but I'm guessing.I do know it had been improved to a 2122X, maybe that is/was the problem.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 08, 2017, 09:46:34 pm
content: Quote from: Gaurav on May 08, 2017, 07:16:16 pmGlad you saw that in time to hit the pause button on the update. Let's see what happens with MrW0lf's unit.