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ADS1198: TEST_AMP clarification

Arash Azarmi
Prodigy 20 points
Part Number: ADS1198
Other Parts Discussed in Thread: ADS1194,

I am working on ADS1194 with Vref=2.4V

CONFIG2 = 0x30

CHnSET = 0x65

Based on datasheet with this config I should expect a 1mV calibration signal to be generated and sampled by ADS. Gain is 12.

I get ~327 counts for p2p of test channel. 

With resolution = 2.4/12*(2^16-1) ,  327 is 1mV

With n=15 , resolution = 2.4/12*(2^15-1) , and  327 is 2mV
Since this is differential we should use n=15, but then p2p=2mV not 1mV.
Does datasheet means p2p by amplitude in description of CONFIG2 register?
TEST_AMP: Test signal amplitude
These bits determine the Calibration signal amplitude.
0 = –1 × (VREFP – VREFN)/2.4mV (default)
1 = –2 × (VREFP – VREFN)/2.4mV
  • 0
    TI__Mastermind 19815 points

    Hi,

    Do you happen to have/use ADS1198 Evaluation kit/board(EVM)?  I suggest try this on the EVM.

    What might be your VREFP-VREFN?

    The calibration signal amplitude should be  –1 × (VREFP – VREFN)/2.4mV (default) depending on your VREFP-VREFN.

    And, according to ADS1198 datasheet Page 5, the test signal voltage swing 1. +/-1 mV or 2. +/- 2 mV; so peak to peak voltage Vpp might be either 2mV or 4mV depending on the TEST_AMP bit setting.

    ADS1198 has a 16 bit ADC, and the MSB is signed bit and the available bits for value are 15 bits.

  • 0 in reply to ChienChun Yang
    Prodigy 20 points

    Hi,
    We don't have eval kit. I set for 0x65 to test calibration
    So –1 × (VREFP – VREFN)/2.4mV  is half of the p2p?

  • +1 in reply to Arash Azarmi
    TI__Mastermind 19815 points

    According to ADS1198 datasheet Page 5, the test signal voltage swing

    1. +/-1 mV or

    2. +/- 2 mV; so peak to peak voltage Vpp might be either 2mV or 4mV depending on the TEST_AMP bit setting.