Teardown: GW Instek SFG-2110 Function Generator. - Page 1
Forum section: electronics / general

author: Kibi
author_rank: Unknown
timestamp: April 08, 2012, 06:38:29 pm
content: I was after a function generator the other day. I looked in the usual places, RS, Farnell etc. but I wanted one right away. A quick Google search revealed a supplier about a kilometer away from my house. Nice.I walked in and made some enquiries. The company does consulting and sells test equipment online, they were really not geared up for "walk-in" customers. They were however, extremely helpful and I walked out with a good function generator at a lower price than RS. Awesome.I took the lid off to take a few quick pictures before putting it to work.I like this thing, it's easy to use and does just what I want it to do. 10MHz is plenty of bandwidth for me for now.I have measured the output witch my Fluke 287 and the selected frequency reads spot on with the Fluke up to about 175KHz before the Fluke's bandwidth is exceeded at 181KHz and then totally stops measuring.When I've got a moment I'll post pictures of the output on the 'scope.

author: Kibi
author_rank: Unknown
timestamp: April 08, 2012, 07:59:04 pm
content: OK, so I have taken some screenshots of the output of the SFG-2110 at different frequencies. I started at 1KHz and worked up to 10MHz.Sine wave output.1KHz10KHz100KHz1MHz - Some attenuation starts creeping in.10MHz - Noticeably attenuated with noise. Although the shape of the waveform is reasonably faithful.Triangle wave output1KHz10KHz100KHz1MHz - Distortion at the peaks. Also, the party stops here for the triangle waveform on this device.Now, for the Square Wave1KHz10KHz - Not too bad so far.100KHz - Distortion is more noticeable now.1MHz - It's going wrong.10MHz - Oh shit. That's supposed to be a square wave!All of the above measurements were taken out of the the main output terminal of the generator.However, the square wave is much better on the TTL output as below.1MHz - TTL Output10MHz - TTL Output.Overall though, I am very impressed with this unit. One shouldn't really be using equipment at the very limit of it's capabilities, so the distortion at the upper end of the spectrum is really not a problem and should actually be expected.I think the SFG-2100 range represents really good value.

author: Unknown
author_rank: Unknown
timestamp: April 08, 2012, 08:05:00 pm
content: Does terminating it into 50 ohm improve the square wave? I'm surprised they spec the square wave up to 10 MHz if the output is so bad. It looks like it will barely meet its <= 25 ns rise time spec.

author: SeanB
author_rank: Super Contributor
timestamp: April 08, 2012, 08:13:00 pm
content: Nice buy! There is a little jitter at the top, probably expected. Most of the time it will be used at the lower end so no problems, and you are aware of it anyway.Looking at the output it was done with a 10x probe direct to the socket, with a very short lead length.I take it you are not living in Bob's lovely handbasket, but are another expat living in the UK.

author: Kibi
author_rank: Unknown
timestamp: April 08, 2012, 08:30:12 pm
content: I used a 50 Ohm terminator and it made no difference with or without it.Quote from: SeanB on April 08, 2012, 08:13:00 pmJa, I've been living in the UK for 14 years now. I went back to Zim at New Year, it was nice to go there on holiday, but I wouldn't live there any time soon.Where abouts in SA are you from?

author: onlooker
author_rank: Frequent Contributor
timestamp: April 08, 2012, 10:36:14 pm
content: It seems in several regards, the DDS3x25 is doing better.1). For a square waveform at 10 MHz, DDS3x25 looks as nice as SFG2110 at 1 MHz.2). DDS3x25 has much more constant output amplitude as frequency goes up.3). Both seemed to suffer the same level of waveform jittering. At 10MHz, both have shown about 10 to 15 ns jittering. However, SFG2110's jittering spanned the entire range, while DDS3x25 takes 2 or 3 discrete values. Maybe, SFG2110 needs Mecha's hack too?

author: T4P
author_rank: Super Contributor
timestamp: April 08, 2012, 11:08:40 pm
content: Quote from: onlooker on April 08, 2012, 10:36:14 pmMost importantly it seems , the only thing unusable on the DDS3x25 is the sync output(input?) and it's a arbFG .Placing a DDS3x25 in a bench dmm type box with a raspberry pi and a 8" screen sounds good to me

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 09, 2012, 01:02:32 am
content: Quote from: Dave.S on April 08, 2012, 11:08:40 pmhow can you say that? have you used and study the synch stable feature in goltek controller? edit the phase calibration file to make the output and synch are in-phase throughout the spectrum/BW? (or out of phase to your heart content?) the only useless thing about 3x25 is 24" screen and standalone controllable operation (it has standalone start-up wave though, but you cant change it offline of PC)looking at sfg110 review, yeah 3x25 fpga stuff performs better, but i'm not sure how the OP is going to do about improving it. what matters most, is what you'll get out of it.

author: onlooker
author_rank: Frequent Contributor
timestamp: April 09, 2012, 02:00:55 am
content: Actually the OP's picture for the 10MHz square waveform is more like one using 20MHz BW limit on my scope. I can't tell whether the BW limit is on or off in OP's picture, though the tag is there and having the same setting as in the TTL picture.

author: SeanB
author_rank: Super Contributor
timestamp: April 09, 2012, 08:42:32 am
content: Quote from: Kibi on April 08, 2012, 08:30:12 pmSunny ( or today rain soon ) Durban.

author: T4P
author_rank: Super Contributor
timestamp: April 09, 2012, 12:14:27 pm
content: Quote from: Mechatrommer on April 09, 2012, 01:02:32 amHaven't used your Goltek but yeah at stock the sync output most people said it is unusable but , i'll go study it .... 24" screenThat's the only downside but k , i was going to rig up a 2nd monitor in front of my bench for a USB microscope and so ... why not rig up the DDS-3x25 for use on that screen too ?

author: saturation
author_rank: Super Contributor
timestamp: April 09, 2012, 07:52:43 pm
content: The model below it is the SFG-1003 had a tear down here:https://www.eevblog.com/forum/product-reviews-photos-and-discussion/teardown-instek-sfg-1003-%28function-generator%29/As I have one of them, it provides outputs very similar to this more advanced model, including the square wave rolls offs that luckily look better on the TTL output; the jitter is also ~ nil there, too.On the 3x25: without mecha's goltek, IIRC you can get it working practically to 20 MHz. But you can still use it to 75 MHz without the sync port. But with Goltek, mecha pushed it to 100 MHz and you can use the sync port.The 3x25 is LVCMOS, so maximum output is 3.5Vpp. For high output voltage or power, place an op amp with suitable gain-bandwidth to buffer its output.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 10, 2012, 05:50:13 am
content: Quote from: saturation on April 09, 2012, 07:52:43 pm3.5Vpp 50ohm terminated, 7Vpp open circuit, you thought me thatyes the synch is usable up to 100MHz "synchronized" with goltek, but resolution limited and you really need to know what you are doing or to edit phase profile.csv. in other word, more diy stuff going on to make it what you want, but for me this is a good exercise as "getting to know your equipment and measurement". but for some people, nothing beats the standalone casing like in the above pictures. some (most?) will refer to it as... "georgous". i agree if the budget allows. its just usb based 3x25 is the "bang buck/?Hz" imho. YMMV.ps: i pushed further the 3x25 output buffer/amplifier to become permanent inside it, now its become... 12x25 output (ie 24Vpp max into Hi-Z) 50ohm inp-Z with external ±15V psu. but thats another OT story.

author: saturation
author_rank: Super Contributor
timestamp: April 10, 2012, 03:18:55 pm
content: You're right mecha, I should have said 3.5Vp, one too many "p"Good to hear you've modd'd the unit even more. The output amp is another weakness, but easy to correct.One can't beat hardware controls to make it easier to setup quickly, my Instek SFG 1005 gets used more often as I often can use < 3 MHz for quick tests, but the Hantek isn't far behind.

author: T4P
author_rank: Super Contributor
timestamp: April 10, 2012, 03:48:02 pm
content: But at the same time there's the dds-3005 that is a hell lot weaker but has a 2.7GHz freq counter and a 14 bit DAC plus 256kSa .5MHz is weak for a 300$ usb AWG and also 2.7GHz is certainly not bad but very expensive for $300 .There's massive tradeoffs to be done with the DDS-3005 and also no sync .A 2.4GHz freq counter can be had for 100$ , and the more speed you have to deal with the less samples . That explains for the short 4kSa length .and the sigilent SDG-1020 is $300 but has 16kSa and only 20MHz sine and 10MHz AW.People , pick your choice .But usually you don't really need 20MHz even , less so with 100MHz ( obtained from goltek )

author: ejeffrey
author_rank: Super Contributor
timestamp: April 10, 2012, 03:57:17 pm
content: QuoteI wouldn't call that TTL output usable, at least not at 10 MHz. A little ringing, corner rounding, or slew rate limiting I can deal with -- I understand that it has finite bandwidth. However, it looks like you have about 8 ns jitter on the outputs. I consider that unacceptable.Out of curiosity does the TTL output look any better when you have the generator make a sine wave?

author: saturation
author_rank: Super Contributor
timestamp: April 10, 2012, 08:25:27 pm
content: Yes, on scope image of this FG2110 TTL output at 10 MHz, that a lot of jitter. On the SFG-1003 the 3 MHz is rock stable on the TTL output and has a fast rise time, at least to the maximum of my 1052e, which is ~ 5ns.The SFG 1003 will not output to the TTL port unless you select square wave.Quote from: ejeffrey on April 10, 2012, 03:57:17 pm

author: Kibi
author_rank: Unknown
timestamp: April 10, 2012, 09:00:31 pm
content: Quote from: ejeffrey on April 10, 2012, 03:57:17 pmNo, square wave must be selected to output on TTL on the SFG-2110. If you select sine or triangle, it just outputs 5v DC.

author: ModemHead
author_rank: Frequent Contributor
timestamp: April 10, 2012, 11:59:24 pm
content: Quote from: saturation on April 10, 2012, 08:25:27 pmAre you sure? I have the SFG-1013 and it will generate the TTL signal for all three waveform shapes, as long as you enable itafterenabling the main output.

author: saturation
author_rank: Super Contributor
timestamp: April 11, 2012, 11:28:11 am
content: Yes. Re-checked. The output of the 1013 should be 5V regardless of your adjustment of Vout, as its TTL. If so, that is better than the 1003 as it can be used for sync signals when using the low voltages on the adjustable Vout port.Quote from: ModemHead on April 10, 2012, 11:59:24 pm

author: nctnico
author_rank: Super Contributor
timestamp: April 11, 2012, 12:06:13 pm
content: Sorry but TTL levels are not necessarily 5V. (IIRC) the TTL specs says anything below 0.8V is 'low' and anything over 1.8V is 'high'.

author: ModemHead
author_rank: Frequent Contributor
timestamp: April 11, 2012, 12:07:49 pm
content: Quote from: saturation on April 11, 2012, 11:28:11 amYes, the TTL output is always fixed 5Vp-p square, even if the Vout is a 5mVp-p sine. Maybe I misunderstood you, but I thought you meant the 1003 would enable the TTL output only if the main output was a square wave. If so, the 1013 is definitely different.