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ADS5282EVM: ADS5282EVM Input with Offset

Part Number: ADS5282EVM

Hi to all,

I would like guidelines in order to provide my application signals with some offset to ADS5282EVM SMA inputs. My application signals range from 0 to -2 Volts. So I would like to add 1V offset in order to take advantage of the full scale range (FSR) of the ADC (-1V to 1V). As far as i have tried the offset is "cutted" from the input circuit of the ADS5282EVM. In that way I am restricted to reduct my signal to 0 to -1 Volts and not take adventage of ADC's FSR.

Thank you in advance!


  • Hi,

    The analog inputs to the EVM are transformer coupled, as can be seen in the schematics for the EVM in the back pages of the EVM User Guide.   Transformer coupling is inherently AC-coupled, and the data converter biases the signal to the desired level after the transformer by the VCM output from the data converter to the center tap of the transformer.   So you signal at the SMA input may be at any level you wish to set it at, but the signal at the data converter will be re-biased and centered around VCM.   If your signal is about 2V peak to peak differential, then you do not need to use the biasing of your signal to get it within range of what the data converter will see.   Since the transformers are nominally 1:1 impedance ratio, your external 2V signal is already about what the data converter needs to see for a full scale signal.   However, the transformer may have about a dB or so of loss in the middle of the transformer passband, and there are series damping resistors after the transformer that will drop some of your signal, so an external 2V signal peak to peak differential will be less that that by the time it gets to the analog input pins.   If you cannot boost your signal amplitude externally, then you may want to reduce the value of those series resistors after the transformer to drop less of your signal.    Or - you could replace the 1:1 ratio transformer with an equivalent 1:2 ratio or even 1:4 ratio transformer to get as much as a doubling of your signal amplitude.    You didn't say what the frequency content of your signal is, so the passband of the transformer may become an issue if your signal is too low or too high a frequency for the transformer.


    Richard P.