Schematic clarification - ZMOD ADC 1410

[Riccardo]

Hello everyone,

I'm going to build an acquisition system with the ZMOD ADC 1410 - 105 mounted on the Eclypse z7.

My signal is not compliant with the input range specified by the reference manual (I'm going to use the high gain option in order to obtain a higher resolution), so I have to add some conditioning circuits before routing the analog signal into the actual scope. 

Is the [-1;1] voltage range defined with respect to the Digilent scope ground? I mean, do I have to put in common some ground lines between the acquisition system and the circuit in which there is the voltage I have to sense or not? 

In order to design the best conditioning circuit, may I have the opportunity to know precisely what is there inside the "amplifier and filter" block?

Thank you for your time

Riccardo

Edited June 24, 2022 by Riccardo
digit error

[JColvin]

Hi @Riccardo,

I have reached out to get some insight into your question so I do not provide any false information.

Thanks,
JColvin

[JColvin]

Hi @Riccardo,

I received some feedback regarding your questions.

With regards voltage range, "The input voltage is applied at the SMA connector. The shields of the connectors are connected to the system GND (which is the common GND connection of the Zmod, Eclypse and also connected to the PC GND via the USB cable. Ale measurements and ranges are relative to that GND reference."

With regards to the black box amplifier and filter, "The Amplifier and filter stage has a high impedance, low bias current, high bandwidth buffer, followed by an anti-alias filter with the characteristic shown in the reference manual (https://digilent.com/reference/zmod/scope/reference-manual ) and concluded with the driver for the ADC." Unfortunately, the decision was made to otherwise not disclose the details of this portion of the design.

Thanks,
JColvin

[zygot]

6 hours ago, JColvin said:

Unfortunately, the decision was made to otherwise not disclose the details of this portion of the design

It's doubtful that having a blank page for Digilent designed FPGA board schematics covering configuration will result in significant lost sales. Ill will? Probably. But hiding details of product schematics is becoming a worrisome habit for Digilent. For a product like the ADC/DAC ZMODs, this is more problematic for customers who have a need for such things for other than educational or hobby related projects. It does represent a troubling change for those who've relied on Digilent as a vendor. Configuring an FPGA doesn't require a detailed schematic, unless the design is faulty. Not having the details of and ADC or DAC circuit might well make such product unsuitable and cost Digilent sales. For configuration customers might be inclined to think that perhaps you have some sort of ingenious trick that might go under the heading of IP, and let it pass as long as they don't have configuration issues ( which includes the JTAG header ). For converter analog conditioning  that's pretty hard to let slide. Customers who need the details are more likely to wonder what is it that they're afraid of me knowing about? 

I guess that it's more important than ever for prospective customers to study the documentation, and in particular the schematic, before making a purchase.

Edited July 8, 2022 by zygot

[AaronNowack]

@JColvin

Can you provide any more details about the filter design of the zmod digitizer and zmod scope/adc? Specifically I want to know if it is linear phase filter such as a bessel filter. I am doing time domain analysis and need to preserve as much of the original pulse shape as possible.

Thank you

- Aaron

Edited March 27 by AaronNowack

[artvvb]

Hi @AaronNowack

Apologies for the delay. We reached out to the engineer who designed the front-end circuitry on both Zmods about your question. Their response is below:

Quote

The Zmod Scope (formerly Zmod ADC) does not have a proper filter with a standard approximation like Bessel, Butterworth, etc. Here filtering simply means a natural BW limit of around FS/2 that serves as anti aliasing filter. The main purpose of the amplifier and filter front end is to adapt the input signal ranges to the ADC full scale input voltage.

The Zmod Digitizer has a proper RLC filter designed for a linear phase Bessel approximation and 75MHz bandwidth. The main idea behind this filter was to keep the group delay as flat as possible for high frequency sampling. However, the real filter response depends on board parasitics and on RLC tolerances. Also, the other analog components might distort the ideal delay response to some extent, but we expect no large delay peaks around the corner frequency as it happens for example with Chebyshev approximations.

Hope this helps,

Arthur