AMX RX

[Willy Bayot]

So now definite choice is LTC2338CMS-18, right?
No more changes?
I am asking this because I am about to place an order.
Updated schematic will not hurt here too...

Do not rush to order as there could still be some updates after the real experiments of Carl.
Up to now, we only have seen simulation results of the XMIT part of Moodz but none for the AFE.
Give Carl a chance to verify the whole system using a simple PCB as described in this post:.

The board I'm working on will combine the TX, RX-AFE, ADC, and power supplies on one board. It will include an IO interface to easily hook it up to a micro dev board for driving the TX and reading the ADC. I will start off by building the TX & AFE only, probably using the bench supply option, to test out RX responses to ground and targets in both current mode & voltage mode. This will give me the information I need to see if any ground compensation needs to be designed in. If it does not, then I can add the ADC and start grabbing data. Even if it does, I can still add the ADC and start writing code while making design changes to the circuit.

There could be some surprise waiting around the corner for us

[ivconic]

I tried to consult ChatGPT on this issue too...

[ivconic]

Folks if you want to push this project to rocket speed; vote me for boss... BUT first give me Carl's, Willy's, Tony's and all yours phone and Viber contacts!
Then all of you will regret because of that!
But the project will run at light speed!
Now as things are going on... probably my grandchildren will see the prototype... in their late ages!

[ivconic]

There are CMS, IMS, and HMS versions, all just different temperature grades. Any will work. TRPBF means "tape & reel" and "lead free." These also don't matter.

I will also try to support the LTC family of converters listed here. They have an almost identical pinout and you can get started for as little as $20.

So now definite choice is LTC2338CMS-18, right?
No more changes?
I am asking this because I am about to place an order.
Updated schematic will not hurt here too...

[waltr]

Yes, I always do that on my designs. If you look at the Power schematic, those rectangular boxes attached to every power rail are for test points. My preference is a 35mil (0.9mm) thru-hole for the wire-loop type as seen in Tony's first Aliexpress link. I don't like as much the SMT type (second link) because I'm always afraid of pulling them off the board.

I also prefer the wire loop thru-hole test points.
We use the SMT ones on board at my work due to lower cost of assembly (can be pick-n-placed). They DO pull off the board when you snag a probe and pull. Luckly, it htypically does not pull the pad off the pcbso can be soleder back on.

We also use the pads, we call them Access Points since you can probe but not connect a probe.
They are handy for troubleshoot is densely pack areas of a board..

[Carl-NC]

Is the LTC2338CMS-18#TRPBF version the right version?

There are CMS, IMS, and HMS versions, all just different temperature grades. Any will work. TRPBF means "tape & reel" and "lead free." These also don't matter.

I will also try to support the LTC family of converters listed here. They have an almost identical pinout and you can get started for as little as $20.

[KingJL]

Great!!!

[Carl-NC]

If you could, will you add adequate test points to the schematic/pcb layout to enhance the test/analysis environment?

Yes, I always do that on my designs. If you look at the Power schematic, those rectangular boxes attached to every power rail are for test points. My preference is a 35mil (0.9mm) thru-hole for the wire-loop type as seen in Tony's first Aliexpress link. I don't like as much the SMT type (second link) because I'm always afraid of pulling them off the board.

[Tinkerer]

If you could, will you add adequate test points to the schematic/pcb layout to enhance the test/analysis environment? The only real downside I have experienced with SMD is my propensity to destroy otherwise functional PCB's with an errant probe slip! My preferred test point is the plated through hole type as the probe point has a secure area to rest in while my eyes wander to a scope or test meter.

https://www.aliexpress.com/item/1005...CH%21187950949

https://www.aliexpress.com/item/1005...d=NFuMFVpRAzkE

[KingJL]

... The board I'm working on will combine the TX, RX-AFE, ADC, and power supplies on one board. It will include an IO interface to easily hook it up to a micro dev board for driving the TX and reading the ADC. I will start off by building the TX & AFE only, probably using the bench supply option, to test out RX responses to ground and targets in both current mode & voltage mode...

If you could, will you add adequate test points to the schematic/pcb layout to enhance the test/analysis environment? The only real downside I have experienced with SMD is my propensity to destroy otherwise functional PCB's with an errant probe slip! My preferred test point is the plated through hole type as the probe point has a secure area to rest in while my eyes wander to a scope or test meter.

[ivconic]

Is the LTC2338CMS-18#TRPBF version the right version?
I have found that specific version at somewhat lower price.
What is the difference among dozen the same LTC2338 chips with so dramatically different prices?

[ivconic]

I have settled on the ADC. I like the one Paul proposed, the LTC2338-18, because it can be driven differentially up to the full 20vpp that I'd like to use. Except for 2 pins, it is pin-compatible with the LTC family I originally considered so I will try to include connection options for either one.

$56 in Mouser!
I can obtain it actually!
I totally forgot that my older son is "American" living in the USA.
But... the price is pfffffff....
Would be good if we could find cheaper yet adequate alternatives.

[Carl-NC]

I have settled on the ADC. I like the one Paul proposed, the LTC2338-18, because it can be driven differentially up to the full 20vpp that I'd like to use. Except for 2 pins, it is pin-compatible with the LTC family I originally considered so I will try to include connection options for either one.

[ivconic]

R1-4: these are for a voltage-mode option, as in Tony's original circuit. Yes, non-zero values will elevate the noise.

ADC: This AFE design probably can't do any better than 84dB SNR. I like the ADC to be at least 6dB better (results in an overall 1dB SNR degradation) so 90dB min. Any of the ADCs we've talked about will work, it's a matter of sample rate, price, and availability.

My intent for this design is 100% SMT (except for the bench supply regs). Sorry, I can't do it with thru-hole. However, I am using the biggest SMT parts I can, preferably SOIC, SOT23, and 0805 passives. I think one of the supply chips may be MSOP, and the ADC (still TBD) may be as well.

The board I'm working on will combine the TX, RX-AFE, ADC, and power supplies on one board. It will include an IO interface to easily hook it up to a micro dev board for driving the TX and reading the ADC. I will start off by building the TX & AFE only, probably using the bench supply option, to test out RX responses to ground and targets in both current mode & voltage mode. This will give me the information I need to see if any ground compensation needs to be designed in. If it does not, then I can add the ADC and start grabbing data. Even if it does, I can still add the ADC and start writing code while making design changes to the circuit.

I hear you. Understand too.
Not you; I am gonna do it in through-hole variant. Probably will not be as good as SMD version, but I don't mind.
But until I start; first I have to see what I can obtain from material.

[Carl-NC]

R1-4: these are for a voltage-mode option, as in Tony's original circuit. Yes, non-zero values will elevate the noise.

ADC: This AFE design probably can't do any better than 84dB SNR. I like the ADC to be at least 6dB better (results in an overall 1dB SNR degradation) so 90dB min. Any of the ADCs we've talked about will work, it's a matter of sample rate, price, and availability.

My intent for this design is 100% SMT (except for the bench supply regs). Sorry, I can't do it with thru-hole. However, I am using the biggest SMT parts I can, preferably SOIC, SOT23, and 0805 passives. I think one of the supply chips may be MSOP, and the ADC (still TBD) may be as well.

The board I'm working on will combine the TX, RX-AFE, ADC, and power supplies on one board. It will include an IO interface to easily hook it up to a micro dev board for driving the TX and reading the ADC. I will start off by building the TX & AFE only, probably using the bench supply option, to test out RX responses to ground and targets in both current mode & voltage mode. This will give me the information I need to see if any ground compensation needs to be designed in. If it does not, then I can add the ADC and start grabbing data. Even if it does, I can still add the ADC and start writing code while making design changes to the circuit.