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Hello everyone!

I would like for someone to explain to me how the input voltages to the ADC's inputs (AINP, AINM, BINP, BINP) are supposed to work in the case of ADS54J60EVM.

In the ADS54J60 manual it is mentioned that the VIC (common-mode input voltage) is 2V while the input (full-scale) is 1.9Vpp. However, the absolute ratings for AINP, AINM, BINP & BINM are from -0.3V to 3.0V.

Unfortunately, there is no output code example in the manual. Furthermore, the ADS54J60EVM is supposed to work (if not modified) as single-mode. So, are the negative inputs (AINM & BINM) tied to the VCM (pin 22) which means that the reference voltage is 2.0V and not 0V (ground)?

So, is the (decoded) voltage range 1.05V to 2.95V to achieve 1.9Vpp? i.e.

1.) AINM = 2V, AINP = 2.95V, (AINP-AINN) = +0.95V

2.) AINM = 2V, AINP = 1.05V, (AINP-AINN) = -0.95V

Is this correct?

I would really appreciate a detailed example as the one Collin Wells gave on a similar case (but regarding a completely different Texas ADC).

Finally, after all the above is clarified, I would like to know if I can modify the output code to NOT use the full-scale, but rather a specific range (such as from -0.2V to +0.2V). This is crucial for the needs of my design as I would increase my SNR by being able to exploit the ADC's precision to my needs

• Anastasios,

This part was not designed to work with a single-ended input and is not recommended to be used in this mode. Also there is no way tp modify the output code per your request.

Regards,

Jim

• Hello Jim,

Thank you for your help. I know that this part (ADS54J60) is designed to work in differential mode, but I'm using the evaluation module (ADS54J60EVM).

As you see, this module has only 3 input SMA ports: one for channel A (INAP), one for channel B (INBP) and one for the ADC clock (optional).

So, could I have a definitive answer on how a single SMA input is translated to digital values (i.e., output code)? What should the default range/amplitude of my signal be? And what is going on with the INAM/INBM inputs if I cannot use them?

I found the above table in Texas ADS1115 user manual but unfortunatelly it doesn't exist in ADS54J60 user manual.

Kind regards,
Anastasios

• Hi Anastasios,

The EVM board ships configured for a single-ended input. Section 5.2.1 of the ADS54J60EVM user guide describes how you can configure the part for a differential input if desired. You would will need to solder SMA connectors to J1 (AINM) and J4 (BINM) in addition to making the user guide board modifications.

By default, the EVM has two onboard baluns per analog input channel to translate a single-ended input signal into a differential signal for the ADC. For reference you can trace the input signal path to the ADC by downloading the EVM schematic under ‘Design Files’ on the ADS54J60EVM page.

The input full scale for this part is 1.9 Vpp. For the default configuration with a single-ended input, the mid-code value will fall at 1.9 / 2^16 * 32766 = ~0.95 Vpp.

Regards, Amy

• Hi Amy,

To be clear: I want to use this EVM using the default configuration, i.e., a single ended input signal in J2 connector.

But still my main question has not been answered: what is the input voltage range that corresponds to the full output code range? Is it -0.95V to +0.95V (from 8000h to 7FFFh) or +2.00V to +3.90V (again from 8000h to 7FFFh)?

I have already consulted the schematics but this information is still unclear as the balun conversion is not well documented.

Kind regards,
Anastasios

• Anastatios,

In order to fullscale this ADC, an input that swings 1.9Vpp is required. The common mode is 2V. This means that the sinusoid needed to achieve full-scale on this ADC is 1.05V to 2.95V. The baluns on this EVM is the ADT1-1WT+ which is 1:1 impedance ratio. Does this answer your question? If not, I'm not sure what you are asking for - please rephrase your question for us.

Thanks, Chase

• Chase,

Yes, I think that your answer covers my question. I had a signal generator producing an 80MHz sine wave connected to channel A (J2 connector) with 1.9Vpp swinging from -0.95V to +0.95V. However, the decoded data that I received in Vivado's ILA were not correct. I will now add a +2V DC offset and I will verify that I'm indeed getting the full-scale code.

One more question: if I transmit just a DC signal (no sine wave) of +3V to J2, will I get 7FFFh continuously? I think that this should be the case, unless somehow the DC signal is filtered.

Kind regards,
Anastasios

• Anastatios,

No, you will not see any tone. Transformers and baluns are passive and because all passive components are inherently AC coupled, this means no DC component of your signal will pass through to the ADC.

Thanks, Chase

• Hello,

I further studied the schematic of the balun. I have a few more questions:

1) If I have an input signal to the single-ended SMA connector (J2) that swings from -0.95V to +0.95V (1.9Vpp) and then try another signal swinging from 0V to 1.90V (again 1.9Vpp) will the balun generate the same differential signals for the ADC chip?

2) Are there any limits to the absolute voltage range the balun work? If I transmit a signal with a DC offset of 10V (so the input signal to the SMA connector is swinging from 10V to 11.90V) will it work the same way as before?

• Hi Anastasios,

Yes the balun will generate the same differential signal for the ADC in either of those cases. The balun used on this EVM is the ADT1-1WT-1+ (https://www.minicircuits.com/pdfs/ADT1-1WT-1+.pdf). Ensure that you do not exceed the RF power or DC current recommendations.

Regards, Amy