Author Topic: Rigol DG4000 series differences  (Read 2852 times)

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Offline jpb

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Rigol DG4000 series differences
« on: June 03, 2013, 02:28:21 pm »
Several times on these forums people have expressed the view that there are no hardware differences between the various Rigol DG4000 models (DG4062,DG4102,DG4162).

Looking at the specs, most of the differences could be just firmware limits, but one major difference is the square wave rise and fall times. For the pulses these are set by the user and could be firmware limits but on the square waves either they are different or they are not.

If they are not different why do Rigol claim much worse specs for the lower models (I know, they wish some to purchase the more expensive models - but at the same time it leaves them to being undercut by other makes)?

The results shown on these forums have, for the built-in square wave (I'm not talking about the arb output square waves) a rise time of around 6.3nsecs for the DG4102 model which is within the DG4162 specs but this was at 20MHz, perhaps it is worse at lower frequency assuming a comparator is used. (It was also described as being into Hi Z so perhaps wasn't 50 ohms though it looked very smooth as if it was well matched.)

It would be very interesting if owners of the different models did identical measurements to settle the question. I'd suggest 10Vpp into 50 ohms at 10kHz, 1MHz and 10MHz say.
It is important to have a frequency range, maximum amplitude and also some sort of load as doing it into say 1Mohm 12pF of a scope might give misleading results.


Edit : Thinking about this further, and to answer my own question, I now think that there is no hardware differences. Square and Pulse are both done using Arb directly which is why they have the same 500ps rms jitter (1/2 a sample point every odd wave as worse case) and Agilent's schemes using a comparator to reduce jitter are not used by Rigol. The extended rise times for square wave are simply included in the wave form in the same way as they are for pulse. The user could bypass them using Arb directly but Arb is limited to a lower frequency (though at the expense of uneven jitter etc more than one waveform could be included in the arb memory).

RE Edit 21st June : I now think there is a difference, they have different bandwidth Bessel filters for square waves and probably pulses. Andyc_722 measures a rise time of 9.8nsecs on a DG4062, KedasProbe measures 6.3 nsecs on a DG4162, Agilent with the 33500 series have a rise time of 8.4nsecs for 30MHz so scaling with this, 9.8 nsecs corresponds to 25MHz (the spec of the DG4062 for square waves) and 6.3 nsecs corresponds to 40MHz (the spec of the DG4102) presumably the square wave rise time for the DG4162 is 5nsecs corresponding to 50MHz.

The rise times cannot be done in software because frequency sweeps are allowed for square waves (they are not allowed for pulse) so the time axis changes with frequency and so square waves must be input as square waves with straight sides but output via a filter to remove the ringing hat is seen when they are implemented by the user in Arb.
« Last Edit: June 21, 2013, 10:41:39 am by jpb »
 

Offline jpb

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Re: Rigol DG4000 series differences
« Reply #1 on: June 21, 2013, 10:54:30 am »
After changing my mind twice, I am now decided that there is a hardware difference between the different Rigol models DG4162, DG4102 and DG4062 and that is in the Bessel filter used for square waves and probably pulses.

Square waves can be frequency swept so that different rise times cannot be coded in firmware (the time scale changes with frequency so the rise time would as well). Andyc_722 measures a rise time of 9.8nsecs on a DG4062, KedasProbe measures 6.3 nsecs on a DG4102, Agilent with the 33500 series have a rise time of 8.4nsecs for 30MHz so scaling with this, 9.8 nsecs corresponds to 25MHz (the spec of the DG4062 for square waves) and 6.3 nsecs corresponds to 40MHz (the spec of the DG4102) presumably the square wave rise time for the DG4162 is 5nsecs corresponding to 50MHz.

The Bessel filter is needed to remove ringing that arises from the elliptic image reject filter. For arbitrary wave forms the Bessel filter is not switched in so rise times are much faster but there is some ringing (people report).

The limitations on sin wave frequencies in the lower models are all just firmware imposed.

Of course users of the DG4062 could use arb and apply an external filter to remove overshoot.

Edited to correct typo (thanks KedasProbe)
« Last Edit: June 21, 2013, 11:49:51 am by jpb »
 

Offline KedasProbe

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Re: Rigol DG4000 series differences
« Reply #2 on: June 21, 2013, 11:31:52 am »
Andyc_722 measures a rise time of 9.8nsecs on a DG4062, KedasProbe measures 6.3 nsecs on a DG4162, Agilent with the 33500 series have a rise time of 8.4nsecs for 30MHz so scaling with this, 9.8 nsecs corresponds to 25MHz (the spec of the DG4062 for square waves) and 6.3 nsecs corresponds to 40MHz (the spec of the DG4102) presumably the square wave rise time for the DG4162 is 5nsecs corresponding to 50MHz.
Seems like a typing mistake, but to be correct, mine is a DG4102 (not DG4162)
Not everything that counts can be measured. Not everything that can be measured counts.
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