Q&A CMR3000

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1. How many bit does CMR3000 have in output?
2. What is CMR3000 resolution? (minimum LSB vs noise)
3. Does CMR3000 have detection range selection?
4. What is the maximum SPI clock rate?
5. Does CMR3000 support 3-wire SPI (CSB tied to GND)?
6. Is the I²C interface disabled when SPI interface is used?
7. Does CMR3000 have self test?
8. Does CMR3000 have reset pin?
9. Does CMR3000 have FIFO function?
10. Does CMR3000 have internal temperature compensation?
11. Does CMR3000 have temperature data output?
12. Can you measure wider than +/-2000 dps range?
13. What does CMR3000 frequency response of 20/80 Hz mean? Can CMR3000 be used to measure human scale gestures?
14. Can CMR3000 be used for OIS?
15. Is CMR3000 providing measurement results from same moment of time?
16. What do you mean by non-linearity?
17. What are the available support tools?
18. How can I ensure my communication works correctly?
19. What is the MAX sampling rate of the CMR3000 demo?
20. What is the purpose of GND area on PWB under the component?
21. What if there is no gap between the PWB and the component?
22. How can I use stand-by mode to reduce the current consumption?

Functionality and specification

1. Q: How many bit does CMR3000 have in output?

A: Output registers are two byte wide i.e. 16 bits. Out of that we utilize 13 bits. Please have a look on the CMR3000 Product Family Specification for details.

2. Q: What is CMR3000 resolution? (minimum LSB vs noise)

A: With 20 Hz measurement bandwidth the noise level is below 1 dpsRMS.

3. Does CMR3000 have detection range selection?

A: Measurement range is fixed 2000 dps.

4. Q: What is the maximum SPI clock rate?

A: It’s 500 kHz.

5. Q: Does CMR3000 support 3-wire SPI (CSB tied to GND)?

A: No. 3-wire SPI is not supported.

6. Q: Is the I²C interface disabled when SPI interface is used?

A: In case of multi slave SPI bus CMR3000’s I²C interface can be disabled with a register command.

7. Q: Does CMR3000 have self test?

A: There is no separate mode for that. Due to used detection principle, the CMR3000 ASIC measures a certain phase shift even when the sensor is stationary (not rotating). In other words, if the CMR3000 output signal is with in the specified limits both the primary and secondary resonant loops are functional and thus the gyro MEMS element is functioning correctly.

8. Q: Does CMR3000 have reset pin?

A: No. Power-on or register command can be used to reset the device.

9. Q: Does CMR3000 have FIFO function?

A: No.

10. Q: Does CMR3000 have internal temperature compensation?

A: No. Detection method gives robust result without compensation.

11. Q: Does CMR3000 have temperature data output?

A: No.

12. Q: Can you measure wider than +/-2000 dps range?

A: Dynamic range is approx +/- 3000 dps. However, this will be limited by the potential offset due to calibration, soldering and temperature dependency.

13. Q: What does CMR3000 frequency response of 20/80 Hz mean? Can CMR3000 be used to measure human scale gestures?

A: Even though gyro can measure for example 2000°/s angular rate, in can not react on indefinitely fast changes of rotation rate. Gyro frequency response describes how fast rotation rate changes can the sensor detect. CMR3000 frequency response is wide enough to measure human motion without a delay in user interface and gaming applications.

14. Q: Can CMR3000 be used for OIS?

A: CMR3000 is optimised for user interface and gaming. As a result, the measurement range is too wide for OIS.

15. Q: Is CMR3000 providing measurement results from same moment of time?

A: SPI: Output register data refresh is enabled when CSB is '1'. Angular rate output registers are refreshed when the MSB register address is written. Use decrement reading to ensure XYZ data from the same moment.
I2C: Angular rate output registers are refreshed when the address of the register is written. Use I²C burst mode while reading to ensure XYZ data from the same moment.

16. Q: What do you mean by non-linearity?

A: Definition of the data sheet parameters is described in section 7 of the CMR3000 Product Family Specification.

Design Support

17. Q: What are the available support tools?

A: Component documentation, samples on breakout board, demokit and C-code sample. Please check our development tools pages.

18. Q: How can I ensure my communication works correctly?

A: A good practise is to read a known fixed register content such as REVID or I2C_ADDR to ensure the write and read operations.

19. Q: What is the MAX sampling rate of the CMR3000 demo?

A: Embedded system can handle 2000 Hz sample rate. Typically PC is the bottle neck limiting the sample rate below 1000 Hz.

20. Q: What is the purpose of GND area on PWB under the component?

A: It minimizes the noise coupled from the PWB. This amount of potentially coupled noise highly depends on the design (product & layout) so the need of the ground plane needs to be defined case by case.

21. Q: What if there is no gap between the PWB and the component?

A: To avoid potential performance and reliability issues, assembly process must ensure gap between the PWB and component. Assembly instructions are documented in TN81 CMR3000 Assembly Instructions.

22. Q: How can I use stand-by mode to reduce the current consumption?

A: Please have a look on Figure 2 in the CMR3000-D0X Product Family Specification. To ensure proper operation, device must be started up in Measurement mode prior changing to Stand By mode.