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ADXRS652 Power Supply Design and Noise Density

Thread Summary

The user inquired about the ADXRS652 gyroscope's noise and ADC resolution requirements. For a 2.5kHz bandwidth, the noise is calculated as 3°/s, which is greater than the 16-bit ADC's resolution of 0.0127°/s. A 12-bit ADC is suggested as sufficient for maintaining in-run bias stability. For high precision, the Vdd can be powered by an LDO, Vratio by a high-precision 5V reference, and AVcc can be tied to Vdd with proper decoupling.
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We use ADXRS652 in our new products and noticed the Rate Noise Density of this gyro is 0.06°/s/√Hz,  does it means if the bandwidth is 2500Hz, the noise is 0.06*√2500=3°/s?

We are going to use a 16bit A/D to convert gyro's output to digital, the resolution should be 0.0127°/s, if the gyro's bandwidth is 2.5KHz, the noise is 3°/s and greater than A/D resolutioin, in that case, seems a 10bit A/D is enough, am I right?

Since the noise density is 0.06°/s/√Hz, a 16bit A/D will enough to whole bandwidth application, is it correct?

Anohter quesition is about the power supply of the ADXRS652, there is 3 power supply pins, Vdd, AVcc and Vratio, based on my understanding, all  power supply pins can be connect to a single supply if high precision is not needed. If high precision is needed,  3 power supplys used to Vdd, AVcc and Vratio separately may be is the best option, but 3 power supply may cost more.

In our case (high precision and high bandwidth needed), we are going to use a LDO (1% precision) for the Vdd, use a high precision 5V reference for the Vratio, but what should we do about the AVcc? If we use LDO to power supply AVcc, may be the precision in not enough, but if we use the 5V reference to the AVcc, may be the 5V reference supply current is not enough cause 3 gyro used on one pcb board.

Is there any applicaion notes about ADXRS652 power supply design or spcefictaion of the AVcc operating current and precision?

  • Thank you for this post!  We sincerely apologize for not responding to this when you made this request.  I won't bore you with the details, but our support model for this forum was not ready for the massive number of questions it created, so some of these important questions were missed.  Are you still working on this?  I am going to use one comment per question to answer them, so that these answers are easier to find in the future. 

  • Question

    We use ADXRS652 in our new products and noticed the Rate Noise Density of this gyro is 0.06°/s/√Hz,  does it means if the bandwidth is 2500Hz, the noise is 0.06*√2500=3°/s?

    Answer

    The noise bandwidth and the cut-off frequency in your filter are not going to be equal, but this approach is correct.  Do you need this much bandwidth?

  • Question

    We are going to use a 16bit A/D to convert gyro's output to digital, the resolution should be 0.0127°/s, if the gyro's bandwidth is 2.5KHz, the noise is 3°/s and greater than A/D resolution, in that case, seems a 10bit A/D is enough, am I right?

    AnswerI have seen application of this principle, as I am aware of successful designs that use 12-bit converters with the series of gyroscopes.  I am not sure how you are arriving at your LSB weighting, but that probably isn't as important as recognizing that your ADC resolution does not have be better than the in-run bias stability in the gyroscope, in order to preserve the best stability performance available in a sensor core.

  • Question

    Since the noise density is 0.06°/s/√Hz, a 16bit A/D will enough to whole bandwidth application, is it correct?

    Answer

    Yes, I believe that 16-bits is enough resolution for this gyroscope.

  • Question

    Is there any applicaion notes about ADXRS652 power supply design or spcefictaion of the AVcc operating current and precision?

    Answer

    I am not aware of any application notes on this topic, but will post a reply if I come across any of them.

  • Question

    Anohter quesition is about the power supply of the ADXRS652, there is 3 power supply pins, Vdd, AVcc and Vratio, based on my understanding, all  power supply pins can be connect to a single supply if high precision is not needed. If high precision is needed,  3 power supplys used to Vdd, AVcc and Vratio separately may be is the best option, but 3 power supply may cost more.

    Answer

    The key insight I can offer on Vratio, is that intends to be the supply that supported the entire signal chain (amp, filter, adc), so that you can manage the signal range, along with the scale variation, with respect to supply.  In designs that I am aware of, the other two supplies can be tied together, with good, local decoupling.