3 Replies Latest reply on Apr 28, 2015 1:39 PM by jota_1939431

    BCM20737S - ADC Noise-free resolution

    dmiya

      I'd like to measure fine value through ADC.

      I'm using adc_SetInputRange(ADC_RANGE_0_3P6V) and adc_readSampleRaw();

      Sample frequency should be default. (I don't call adc_setAdcSampleFrequency()).

       

      (1) What is noise-free resolution?

      ENOB in above configuration looks 13bits.

      The noise-free resolution will be lower number of bits I think.

       

      (2) What is accuracy of reference voltage?

      I don't input external known voltage as reference input.

      And this also affects ADC result.

      Is it +/-5%, +/-2% or less value like +/-0.1%?

        • 1. Re: BCM20737S - ADC Noise-free resolution
          jota_1939431

          Hello Daisuke,

           

          1.  The most that we can achieve is really 13 ENOB @ 5.859KHz, going down to 10 ENOB @ 187 KHz

          2.  The A/D result is +/- 2%

           

          Here is a related post: BCM20732S ADC Configuration

           

          Here is also other info compiled about ADC:

           

           

          GPIO and ADC Voltage Range Questions:

           

          1. What is the recommended maximum voltage that can be applied to any pin relative to VDDIO?
            1. [JT] – 3.63V

          2. What is the Absolute Range of voltage that can be applied to the ADC?
            1. [JT] – Absolute Range of voltage that can be applied is 0V to 3.63V

          3. What is the ADC Reference Voltage?
            1. [JT] – The ADC Reference voltage is the Core Voltage which is always 1.2V

          4. How is power consumption affected by the input voltage range to the ADC?
            1. [JT] – The voltage is clamped at the low end by the Core Voltage and at the high end by the VDDIO Voltage

           

          Thanks

          JT

            

          • 2. Re: BCM20737S - ADC Noise-free resolution
            dmiya

            Thank you for your answer j.t.

            Let me check this again.

            By (2), ADC result has +/- 2% error even if the ENOB is 13bits@5.859kHz.

            It means when I use internal voltage as reference, the ENOB of absolute value will be ~5bits?

            • 3. Re: BCM20737S - ADC Noise-free resolution
              jota_1939431

              Hello Daisuke,

               

              You should get close to 13 bits.

               

              JT