Author Topic: DDS vs TrueArb, something is wrong? or DDS is no go for timing sensitive signal  (Read 2546 times)

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Offline RoadRunner

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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.pdf
 Please take a look at attached images. 

« Last Edit: May 07, 2017, 08:09:26 pm by Gaurav »
 

Offline awallin

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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.
 

Offline Electro Fan

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Might be worth checking to make sure the latest firmware is installed:

http://www.siglentamerica.com/gjjrj.aspx?id=15

FWIW....

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 ARBs

Siglent'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
 

Offline RoadRunner

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Might be worth checking to make sure the latest firmware is installed:

http://www.siglentamerica.com/gjjrj.aspx?id=15

FWIW....

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 ARBs

Siglent'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

Will try to update firmware and see if this makes any difference.
 

Offline pascal_sweden

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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?
 

Offline RoadRunner

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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?

though 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.

 

Offline Electro Fan

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Might be worth checking to make sure the latest firmware is installed:

http://www.siglentamerica.com/gjjrj.aspx?id=15

FWIW....

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 ARBs

Siglent'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

Will try to update firmware and see if this makes any difference.

Just 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
 

Offline RoadRunner

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Might be worth checking to make sure the latest firmware is installed:

http://www.siglentamerica.com/gjjrj.aspx?id=15

FWIW....

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 ARBs

Siglent'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

Will try to update firmware and see if this makes any difference.

Just 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

oops ,

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.
 

Offline tautech

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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.  :-//
Avid Rabid Hobbyist
 

Offline Electro Fan

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Might be worth checking to make sure the latest firmware is installed:

http://www.siglentamerica.com/gjjrj.aspx?id=15

FWIW....

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 ARBs

Siglent'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

Will try to update firmware and see if this makes any difference.

Just 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

oops ,

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.

Glad you saw that in time to hit the pause button on the update.  Let's see what happens with MrW0lf's unit.
 


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