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ADS1294: Data converters forum

Part Number: ADS1294

Page 32 of the Datasheet describes the input differential dynamic range equal to 2ref/gain,

But is described later:The 3-V supply, with a reference of 2.4 V and a gain of 6 for ECGs, is optimized for power with a differential input signal of approximately 300 mV For higher dynamic range, use a 5-V supply with a reference of 4 V (set by the VREF_4V bit of the CONFIG3 register) to increase the differential dynamic range.

The 3-V supply, with a reference of 2.4 V and a gain of 6, The maximum input differential voltage should be 800mV, why 300mV? How to calculate 300mV?

In addition, when the pharmaceutical industry requires input short circuit, the equipment noise should be less than or equal to 1 microvolt under 1 kHz bandwidth. Can ADS1294 meet the requirements?

Thanks for your help

  • When Vref and gain are set, the Differential Full-Scale Range is from -Vref/gain to +Vref/gain

    so,

    if Vref = 2.4V, gain = 1, the Differential Full-Scale Range  is from -2.4V/1 to +2.4V/1

    if Vref = 2.4V, gain = 6, the Differential Full-Scale Range  is from -2.4V/6 to +2.4V/6

    "The 3-V supply, with a reference of 2.4 V and a gain of 6 for ECGs, is optimized for power with a differential input signal of approximately 300 mV."  means if using 3-V supply and Vref=2.4V and Gain=6, the "power" is optimized around 300mV, but you could still inject signal as long as it's within the range, but it may almost hit the limits(bounds), e.g. upper bound(+2.4V/6) or lower bound(-2.4V/6), which people usually want to avoid acquiring signals that are close to the limits(bounds). In that case, suggest to either reduce the gain or use 5-V supply with 4V Vref.

    Regarding to the input short noises questions, it will depend on the analog supply, Vref, sampling frequency, data rate and gain users set/select as well as how users design their PCBA, you may refer to page 22~23 Table. 1~4

    e.g. Table 3 noises are measured under the conditions of "High-Resolution Mode 5-V Analog Supply and 4-V Reference",

    When the data rate is set to 4000SPS, this gives band width around 1048Hz, and if the PGA gain is set to 12, then the noises will be around 1.1uV RMS. So, based on these tables, you can decide which configurations and whether the noises under those configurations meet your applications/requirements.

    I suggest to buy an evaluation kit/board(EVM) to test and evaluate.

    Thanks

  • 800mV optimization can not be reduced to such a small size as 300 mV, this 300mV can be understood if it is +300mV~-300mV, please confirm!

  • Hi,

    The optimized range for the situation of 3-V supply and Vref=2.4V is -300mV to 300mV when the bound is -400mV to 400mV