What is rate noise density and what are its practical considerations? How does one design around it?
Rate Noise density is a parameter which allows the user to determine the overall noise of the gyro in their application, depending upon the bandwidth which they choose. its not so much something which should be "designed arund", rather its a consideration which needs to be taken into account depending on the needs of the application.
The ADXRS6xx family of gyroscopes allows the user to configure the bandwidth of the device by adjusting the value of the capacitor between Rateout and SUMJ. This forms a first order RC filter with an internal resistor that is trimmed to 180kOhm. the higher the bandwidth, the faster the response time of the gyroscope to transitions from positive to negative rate input, however the higher bandwidth will allow more signal content, and subsequently more noise, to appear on the output of the gyro.
its really quite simple to convert from rate noise density to RMS noise. the following equation is all you need:
NoiseRMS = RateNoiseDensity*sqrt(bandwidth*1.6)
you can then multiply the RMS noise figure by a factor of 6 to approximate resulting the peak to peak noise.
with the information above, and an understanding of the intended application, its up to the user to decide for themselves what bandwidth would be acceptable for the application, and what that means in terms of the expected noise of the gyroscope.
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