New Bipolar Boost TX and Front End

[KingJL]

Looking good! I have wound a mono 300 mm coil at around the same specs 328uH 1.7 ohms ready for testing but over the last couple of days, have been busy getting the vacuum former ready to do some coil shells while the weather has cooled a little, It's been hot so progress has slowed for workshop machines. Tonight I might hook up the test coil and take some measurments.

With the current timings, DAMP might be significantly late (like anywhere from 250ns to 1usec too late). I have a new version of the Vivado files that I can release where the DAMP timing is parameterized and can be set in the block design and then regenerate and export the bitstream for the SDK. One of the first software targets will be to automate the DAMP timing setting.

[Mdtoday]

Finally finished (almost) loading the TX/RX PCB. R9 & R11 yet to be loaded as I am waiting a shipment of 805 & 1206 resistors kits. They have the <1 ohm values needed.
[ATTACH=CONFIG]49154[/ATTACH]
[ATTACH=CONFIG]49155[/ATTACH]

Still need to wind a mono coil for testing. Target parameters for the coil are 10.25" diam, 320 uH, 1.5 ohm.

After preliminary checks and firing up the TX, I will focus on validating the timing of all of the TX/RX signals and the software code to auto tune the start of the DAMP signal. That should all start happening in about 2 weeks.

Looking good! I have wound a mono 300 mm coil at around the same specs 328uH 1.7 ohms ready for testing but over the last couple of days, have been busy getting the vacuum former ready to do some coil shells while the weather has cooled a little, It's been hot so progress has slowed for workshop machines. Tonight I might hook up the test coil and take some measurments.

[KingJL]

TX/RX PCB Loaded

Finally finished (almost) loading the TX/RX PCB. R9 & R11 yet to be loaded as I am waiting a shipment of 805 & 1206 resistors kits. They have the <1 ohm values needed.



Still need to wind a mono coil for testing. Target parameters for the coil are 10.25" diam, 320 uH, 1.5 ohm.

After preliminary checks and firing up the TX, I will focus on validating the timing of all of the TX/RX signals and the software code to auto tune the start of the DAMP signal. That should all start happening in about 2 weeks.

[Mdtoday]

I just ordered this today to use as the cable for my DD.

That cable looks good

[Mdtoday]

@MDtoday
Yes, just asking questions. Thanks for explaining your thoughts.
I did look at the Gerbers pretty close and did think of a split between TX and RX circuits but came to same possible issue of timing traces crossing the split. The solid ground plane on inner 2 plus the ground fills on other layers should be good.

Hi Waltr, yes all good input, it?s the way we get things done isn?t it, everyone adds a bit of knowledge, and ferrits out the problems, it?s great! Thanks for for your input, it is very much appreciated.

[KingJL]

... 1- The 20V path on layer In2 goes to D1 through a single small via. Is this one via large enough and have low enough impedance? Adding a few more vias may be better...

Good catch... extended the zone on the power plane feeding D1-pad2 and added two more vias and 1mm tracks to pad 2 of D1.

And yes, the CMOD-A7 only has 1 pin connected to GND. Thank you @waltr for the feedback.

[KingJL]

I've got to do that myself. I want to have a DD and a mono with TX at ~320. Haven't decided on the RX for the DD... factors to consider: (1) balanced (RX = TX) should provide the best noise/soil condition performance. (2) RX > TX probably provides slightly better RX signal in ideal conditions (if conditions are ideal, probably shouldn't be using DD).

I just ordered this today to use as the cable for my DD.

[waltr]

@MDtoday
Yes, just asking questions. Thanks for explaining your thoughts.
I did look at the Gerbers pretty close and did think of a split between TX and RX circuits but came to same possible issue of timing traces crossing the split. The solid ground plane on inner 2 plus the ground fills on other layers should be good.

[Mdtoday]

Part of this, I can answer. I will let @Mdtoday address the V4 issue .

@Waltr, thanks for your input, much appreciated. The V4 shielding was arrived at after studying JL?s layout, knowing the circuit functions /current paths,testing the original board design with shielding, scoping the signals etc, then of course adding some practicality for mounting.
The final version will have slots for the 2 Cmod-A7 socket strips as per the original internal enclosure which works well.
The shield is meant to help reduce external RFI type noise entering the RX, not EMI out this would be the job of the external enclosure in this case.
Those drawings a very preliminary.

I agree with the use of star grounds in some cases but with reference to the actual board layout, I will say that it is very good, given the requirements and from experience with high resolution converter layouts that sometimes star grounds can cause more problems than they are worth if not done right,like increasing trace inductance, hence ringing. Sometimes a complete ground plane is the answer.
There are no massive currents circulating, if there were, for sure, the design would need to be layed out different.

If you look at the circuit and layout, the ADC is far enough away from the ground currents flowing from TX and the CMOD-A7 ground but still close enough to the ground connector.
It could possibly be improved by splitting the ground plane diagonally from near power connector to top right corner of board but then you will still have logic traces crossing that split causing issues, so I don?t see much advantage.

I agree on the high resolution converter grounding requirements though, they can be fussy.

[KingJL]

Looks like you have opposite problem to me, my firefox browser stopped giving the spell check while on the geotech forum, and I fiddled around for a while and couldn't figure out why. Just recently I installed chrome, and lo and behold, the spell check was back! So I figured it might be outdated browser problem, but I can't say for sure.

Much like the ability to view inline jpeg and png in forum posts... one day I had it... the next I didn't (and I still don't have it)!

[dbanner]

I am using chrome!!

Looks like you have opposite problem to me, my firefox browser stopped giving the spell check while on the geotech forum, and I fiddled around for a while and couldn't figure out why. Just recently I installed chrome, and lo and behold, the spell check was back! So I figured it might be outdated browser problem, but I can't say for sure.

[KingJL]

I had the same problem with firefox browser, one day it just stopped working. But with chrome browser, the spell check works fine. Very strange.

I am using chrome!!

[dbanner]

BTW: Some how my editor envirionment has changed where I no longer have spelling issues identified. How do I turn this back on... doesn't seem to be option on the editor menu.

I had the same problem with firefox browser, one day it just stopped working. But with chrome browser, the spell check works fine. Very strange.

[KingJL]

... More effective is the PCB design, particularly Ground paths, to keep the RX signal quiet.

I do work with very sensitive analog circuits. We (where I work) have found that Ground paths are very, very important for quiet analog and high count ADCs.

That is why on this PCB, not only do we have a dedicated ground plane layer, but both the top and bottom layers have a ground "pour" over the full dimension of the board and all 3 layers are stitched together with an array of via's (one array spaced 10mm apart and another array offset by 5mm in both x and y directions with the same spacing), thus ensuring that there is a maximum path length of 14mm for a ground return of any signal. Also key areas have extra stitching via's to ensure the shortest paths through GND (especially for the ADuM4120's and the LTC2378 REF).

[waltr]

JLKing,
Thanks for the explanation of the RX_Blank function. This makes sense for where U2D is connected.

I was also thinking shielding the RX analog circuits only.
Idea being to keep switching and processor noise out of the RX signal.
However, I do not think that simply shielding this part of the circuit will do anything useful since as you said, the RX is connected to TX circuits.
More effective is the PCB design, particularly Ground paths, to keep the RX signal quiet.

I do work with very sensitive analog circuits. We (where I work) have found that Ground paths are very, very important for quiet analog and high count ADCs.