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Original question:

ADS1015: Analog input voltage

ADS1015: Question Regarding Signal Amplification and Full-Scale Range (FSR) in ADS1015 ADC

EIFFEL CHRISTY
Prodigy 90 points
Part Number: ADS1015


Tool/software:

Hi Team,

We are using the ADS1015 ADC IC to detect sine and cosine analog signals from the sensor, which outputs a voltage range of 100mV to 600mV.

I have a question regarding the ADS1015: If the full-scale range (FSR) is set to ±2.048V in the IC configuration, does the ADS1015 internally amplify the input signal to match the ±2.048V range?

Or does the term "programmable gain amplifier" in the datasheet simply denote the voltage range that the ADC can support, without actually amplifying the input signal?

  • 0
    TI__Expert 8130 points

    Hi Eiffel Christy,

    EIFFEL CHRISTY said:
    If the full-scale range (FSR) is set to ±2.048V in the IC configuration, does the ADS1015 internally amplify the input signal to match the ±2.048V range?

    What setting the FSR range to ±2.048V does is it changes the value of LSB. At this setting, 1LSB = 1mV. You can measure signals up to ±2.048V in this configuration, and a full scale (0x7FF) reading would correspond to +2.048V. It does not mean that the input signal is somehow automatically scaled up to ±2.048V.

    If your signal is between 100mV and 600mV, setting the FSR to ±1.024V for example, would give you better dynamic range. Now 1LSB represents 0.5mV. There are fewer ADC codes that would go unused to capture your input signal in this configuration.

    What are the sine and cosine analog signals from the sensor that you would be detecting? Keep in mind that the maximum data rate of this device is only 3.3kSPS. Consider if this is enough to capture your AC signals accurately, as this device is typically intended for DC measurements. Also, the device can only measure negative "differential" values (as in the absolute voltage at AINN is higher than the voltage at AINP), it cannot measure absolute negative signals with respect to GND. This means that the voltage value of your AC signals would have to remain positive with respect to GND throughout their cycle.

    Best Regards,

    Angel

  • 0 in reply to Angel Rodriguez de San Miguel Bermudez
    Prodigy 90 points

    Hi Angel.

    Thank you for the explanation. 

    Our sine waves are varying as below between 1.5v to 1.8v : 

    So if it is not amplifying the signal actually then what should be best configuration to detect above signal? 

  • 0 in reply to EIFFEL CHRISTY
    TI__Expert 8130 points

    Hi Eiffel Christy,

    Your signal shown varies around 0.52V. For this you could use the ±1.024V FSR configuration and have the signal as a differential input.

    If the signal is from 1.5V to 1.8V as you mention the max-min difference is smaller (0.3V), so you could actually use the ±0.512V FSR configuration and get better dynamic range (less number of ADC codes that go unused).

    Best Regards,

    Angel

  • 0 in reply to Angel Rodriguez de San Miguel Bermudez
    Prodigy 90 points

    Hi Angel

    Based on my graph, the voltage varies between 1.5V and 1.8V, resulting in a delta of 0.3V. However, when I set the FSR to ±0.512V, the ADC consistently outputs the maximum value of 2047.

    From my understanding of the IC, to properly utilize the ±0.512V FSR range, the input voltage should vary between 0V and 300mV. Could you confirm if this is correct?

  • 0 in reply to EIFFEL CHRISTY
    TI__Expert 8130 points

    Hi Eiffel Christy,

    Based on your graph the voltage seemed to vary between 1.95V and 1.43V, which is closer to a delta of 0.52V.

    The ADS1015 can accept differential measurements, meaning the output code corresponds to the voltage difference between two input pins.

    For example, if 1.8V are applied to AIN0, and 1.5V to AIN1, and the MUX is set to the AIN0-AIN1 setting, then the differential voltage measured is 0.3V, and the output code would correspond to this.  ±0.512V FSR range configuration would be valid in this case.

    Are you configuring the part for as single ended measurements?

    Do you have a schematic available for this?

    What does your 1.5V-1.8V signal share the same GND reference as the ADS1015?

    Best Regards,

    Angel