CRM PinPoint

Sehr platzsparendes, kostengünstiges, präzises einachsiges MEMS-Gyroskop, mit branchenführenden Werten bei Vorspannung und Rauschen über den Temperaturbereich hinweg.

PinPoint® ist das kleinste MEMS-Gyroskop in unserer Produktpalette. Dieses sehr platzsparende, robuste Gyroskop eignet sich für einen außerordentlich breiten Anwendungsbereich. Es ist sowohl in flachen (In-Plane) (CRM100) als auch in orthogonalen (CRM200) Gehäusen erhältlich, die in Kombination die Messung von drei Freiheitsgraden (Roll-Nick-Gier-Winkel) auf einer einzigen Platine ermöglichen. PinPoint® bietet vom Benutzer wählbare Geschwindigkeitsbereiche von 75°/s bis 900°/s. Es sind auch Versionen mit hohen Geschwindigkeitsbereichen (bis zu 2700°/s) erhältlich.

Produktionsstatus: In Produktion
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Verfügbarkeit: Verfügbar
Kundenanwendungen: Neue und bestehende Anwendungen


CRM100

CRM102.1

CRM200

CRM202.1
Supply Voltage3.3V3.3V3.3V3.3V
Angular Random Walk0.2º/√hr0.8°/√hr0.2º/√hr0.8°/√hr
Bias over Temperature±1 ̊/sec±36 ̊/sec±3 ̊/sec±36 ̊/sec
Bias Repeatability±0.14 ̊/s rms±0.15 ̊/sec±0.14 ̊/sec±0.15 ̊/sec
Bias Instability12°/hr80°/hr12°/hr80°/hr
Bandwidth (nominal)5 - 160 Hz (User Selectable)5 - 160 Hz (User Selectable)5 - 160 Hz (User Selectable)5 - 160 Hz (User Selectable)
Operating Temperature-40°C to +85°C-20°C to +85°C-40°C to +85°C-40°C to +85°C
Scale Factor2.75 LSB/°C2.75 LSB/°C2.75 LSB/°C2.75 LSB/°C
Typ. Current Consumption4mA4mA4mA4mA
Angular Rate Range User configured for ±75, ±150, ±300 & ±900±900°/s to ±2700°/s User configured for ±75, ±150, ±300 & ±900±900°/s to ±2700°/s
Operational Shock500g 1ms (maximum)500g 1ms (maximum)500g 1ms (maximum)500g 1ms (maximum)
Bias over Temperature±1 ̊/sec±36 ̊/sec±3 ̊/sec±36 ̊/sec
Datasheet Datasheet Datasheet Datasheet
Does PinPoint® use a magnet?

No, PinPoint® uses piezoelectric transducers and therefore is not sensitive magnetic fields and does not produce a magnetic field.

If we power two PinPoint®'s from one power supply, will they interfere with each other?

Due to the very low current used by PinPoint®, interference through the power supply is very unlikely. However, we do recommend using “star points” and good tracking policies to give optimal isolation.

Is PinPoint® affected by magnetic fields?

No, the transducers within PinPoint® are not sensitive to magnetic fields.

Is the PinPoint® sensitive to gravity or linear acceleration?

We do specify sensitivity to gravity and linear acceleration, but because PinPoint® uses a balanced ring as the vibrating structure, it is very resilient to gravity, linear acceleration and vibration.

What happens if PinPoint® is over-ranged?

In analogue output mode it will give a potentially useful rate measurement output above the preset ‘maximum’ rate range, but performance (i.e. linearity) is not guaranteed.

The nominal zero bias is ½Vdd; 1.65V. The maximum specified rate range is scaled to occur at ±1.0V of the nominal zero bias. The scale factor remains linear to at least 10% beyond the ‘specified’ limit of ±1.0V (i.e. ±300º/s) to allow for tolerances, and beyond this linear range the output will not be guaranteed to be linear and will saturate when it is within approximately 100mV below the supply rail. So, a PinPoint® gyro configured to ±300º/s ‘maximum’ rate range will actually measure up to ±465º/s [(1,650mV – 1,000mV – 100mV)÷ 3.3mV/º/s = 165º/s].

Can you explain the internal sampling scheme used within PinPoint®, covering resolution, sampling rate and any averaging?

The internal ADC has a Successive Approximation Register (SAR) architecture.

Can PinPoint® be set up differently in different applications?

The simple answer is ‘Yes’. To answer the question more fully we need to consider the two output modes of PinPoint®; analogue and digital.

Analogue Output:
There are two possible methods of improving the output resolution and accuracy; (i) Oversampling and, (ii) Switching the measurement range.

(i) Over-sampling; assuming you are, say, digitizing the output at 1,000Hz (i.e. every 1ms) and converting through a 10-bit ADC. By over-sampling, say at 4,000Hz (i.e. every 250µs), and then averaging the four measurements, this
will improve the output accuracy as it will filter the noise from the gyro. This improves accuracy, but not resolution.

(ii) Switching the measurement range; with PinPoint® it’s possible to change the measurement range from, say 300º/s to 75º/s, this will have an effect of a fourfold increase in resolution. To do this you will need to have the ability to ‘talk’ to the gyro through the SPI interface. Through the SPI you can alter the scale factor of the analogue output. It is necessary to ‘reset’ the gyro, in other words it will be effectively switched off and on again, a process which can take
up to 0.3s. This will not have any adverse effect on the function or performance of the gyro, but it is a consideration for the application system design.

Digital Output:
In the case of digital output mode the option of over-sampling is redundant. Through the SPI the rate range can be switched between any of the six pre-determined values; 75º/s, 150º/s, 300º/s or 900º/s. This doesn’t involve a hard-reset of the gyro as described above for the analogue output mode, and so no loss of signal occurs.

What is the maximum rate range for PinPoint®?

As currently configured PinPoint® is specified to deliver full performance up to 900º/s from both the analogue and digital output channels, but it is in fact capable of measuring above this.

The gyro output, in analogue output mode, clamps at 1,250º/s and should not saturate or invert below this level of rate input. The digital output mode is clipped at 1,024°/s.

What resolution ADC is used within PinPoint®?

PinPoint® is inherently an analogue sensor which provides an optional digital output. The ASIC has an internal 10-bit ADC but with oversampling it is effectively a 12-bit ADC. This is explained further below.

The internal ADC has a resolution of 10-bits, and a full scale range of +/-1.024V. If, for the purpose of explanation, we consider the +/-300°/s dynamic measurement range only, then the Technical Datasheet (CRMnnn-00-0100-132) defines the analogue scale factor as 3mV/°s. So, the 10bit ADC has a full scale range of +/-341.333°/s [i.e. 1.024V ÷
3mV/°/s].

Internally, the PinPoint® gyro ASIC is sampling at the resonant frequency of the silicon MEMS ring sensor, which is approximately 22kHz. It is continually calculating a running total of the last 16 samples, which is a 14-bit number. On the falling edge of the SPI_CLK, the 14-bit number is sign extended to a 16-bit number and output to the host. If bit 16 is ‘1’ the sign is –ve, if it is ‘0’ sign is +ve. Bit 15 is not used.

The digital scale factor for a dynamic range of +/-300°/s is 24 bits/°/s, or 1/24°/s per lsb. The range of the ADC is +/-341.333°/s (see above). That implies an ADC of 14 bits [i.e. 682.666°/s ÷ 1/24°/s = 16,384 = 214].

By oversampling the signal, the apparent resolution of the ADC has been improved from 10 bits to 14 bits. However, the improvement is only achieved because of the noise that is inherent in the sensor signal. It is well understood that the effective resolution of an ADC can be improved by the addition of noise and oversampling. The apparent resolution of the ADC improves by 1 bit for every doubling of the sample rate. However, the effective resolution only improves as the square root of the increase in sampling rate (the additional noise subsides as the square root of the oversamples).

So, although the 16 times oversampling has given an apparent increase in resolution of 4 bits, the effective increase in resolution is actually 2 bits. For that reason, the ADC in the PinPoint® is described as „effectively a 12 bit ADC“.

Can you tell me more about the temperature sensor used within PinPoint®?

The temperature sensor is a functional block on the ASIC inside the gyro. It is used to perform internal thermal compensation of the gyro. It is provided as an output in the digital SPI message and thus can be used by the system for overall thermal compensation. It’s not available on the analogue output.

Can you tell me what the maximum voltage of Vref_cap is likely to be, to enable me to select a capacitor?

Vref is generated to provide a voltage which tracks half of the supply voltage, that it Vdd/2. Vref is used internal to PinPoint® and therefore it is important that it maintains stability and is not disrupted in any way. Since the maximum recommended Vdd is 3.6V, the voltage on Vref_cap is unlikely to exceed 1.8V. As far as the capacitor is concerned, we would recommend a 100nF value rated to 10V and it should be of the X7R ceramic type, mounted close to the Vref_cap pin. The track from the capacitor to the Vref_cap pin should not pass through a PCB via. The minimum rated voltage for the capacitor should be 6V, but to reduce stress on the capacitor and increase reliability, we recommend a rating of 10V. In summary, we recommend that the Vref_cap should be: 100nF, X7R MLCC, SMT package mounted close to the Vref_cap pin, rated at 10V and avoiding the use of vias.

Do you recommend using the Analogue or Digital Output of the PinPoint® gyroscope?

PinPoint® is primarily an analogue gyroscope. A digital block is used to digitise the analogue signal and output it in a digital data stream, on the SPI bus. The ADC used within Pinpoint is effectively a 10 bit device and with oversampling, the resolution becomes effectively 14bits, but the accuracy typically 12bits. In general, the analogue output provides slightly better performance.

If the user needs an analogue signal, then the recommendation is to use the analogue output.

If the user intends to process the data digitally, then the SPI is recommended. If higher performance is required, it is recommended that a higher accuracy ADC scheme be used instead, where performance can be enhanced with high sampling rates, and digital filtering.

What additional components are needed for the gyroscope to work?

For PinPoint®, four additional capacitors are needed for correct operation.

Can I use the Vref_cap as a voltage reference for my system?

You can, but it is important that the Vref maintain stable and is not disrupted in any way. We recommend that the Vref_cap signal is adequately buffered with a ultra-high impedance voltage follower.

Can a number of PinPoints® share a common SPI bus?

Yes, that is one of the features of an SPI bus. The “Slave Select”, (SS) pins are used to select each individual device.

What is the resolution of the PinPoint®?

If the digital output is used, then the resolution is taken as the least significant bit of the data in the message. This resolution depends on the rate range the gyroscope has been set up for. The datasheet provides the scale factor in terms of lsbs/°/s. The reciprocal of this number gives the weighting of the lsb, or the digital resolution.

If the analogue output is used, then the best resolution achievable can be taken as the bottom part of the Allan Variance plot, i.e. the bias instability for the device. An alternative definition for analogue resolution is the minimum observable difference observable at the output for a change to the input. This is related to noise and is normally taken as the input signal which will cause the output to be greater than the noise output.

Is the PinPoint® repairable?

No. It has been designed for high volume applications with a superior performance to cost ratio. It is therefore not economic to consider repairing a damaged device.

Can I change the dynamic range on the PinPoint® gyro 'on the fly'

Q: I see that it’s possible to change the dynamic range on the PinPoint® gyro, can this be done ‘on the fly’, in other words when our application needs the lower rate range and higher resolution, can we ‘switch’ to a lower rate range and will it give us higher resolution?

A: The simple answer is ‘Yes’. To answer the question more fully we need to consider the two output modes of PinPoint®; analogue and digital.

Analogue Output:

There are two possible methods of improving the output resolution and accuracy: (i) Over-sampling and, (ii) Switching the measurement range.
(i) Over-sampling; assuming you are, say, digitizing the output at 1,000Hz (i.e. every 1ms) and converting through a 10-bit ADC. By over-sampling, say at 4,000Hz (i.e. every 250µs), and then averaging the four measurements, this will improve the output accuracy as it will filter the noise from the gyro. This improves accuracy, but not resolution.

(ii) Switching the measurement range; with PinPoint® it’s possible to change the measurement range from say 300º/s to 75º/s, this will have an effect of a fourfold increase in resolution. To do this you will need to have the ability to ‘talk’ to the gyro through the SPI interface. Through the SPI you can alter the scale factor of the analogue output. It is necessary to ‘reset’ the gyro, in other words it will be effectively switched off and on again, a process which can take up to 0.3s. This will not have any adverse effect on the function or performance of the gyro, but it is a consideration for the application system design.

Digital Output:

In the case of digital output mode, the option of over-sampling is redundant.

Through the SPI the rate range can be switched between any of the four pre-determined values; 75º/s, 150º/s, 300º/s or 900º/s. This doesn’t involve a hard reset of the gyro as described above for the analogue output mode, and so no loss of signal occurs.

Can the gyros be programmed by our host system during fitment to set the rate ranges accordingly to the application?

Yes, this is possible and allows the user to set up the gyro depending on its orientation in the application.

Analogue Output: If the analogue rate output is being used, then via the SPI digital interface it is possible for the host system to set the analogue measurement range.
Digital Output: The host system can set the required measurement range.

Do I need to separate DATA_IN or DCLK, to prevent the CRM100 from getting unwanted commands?

Q: We have another sensor on the same SPI (with a different slave select, /SS). I understand we need to separate DATA_OUT by a gate to achieve high Z if the device is deselected. The question is, do we also need to separate DATA_IN or DCLK, to prevent the CRM100 from getting unwanted commands?

A: DATA_IN and DCLK do not need to be separated. PinPoint® would only respond to commands if the /SS input line is taken low.

We have noticed that if the gyro is over-ranged or shocked, the Checksum is incorrect. Also, if we command a built-in-test (CBIT), the Checksum can be incorrect too. Can you explain why this happens?

The checksum is calculated before the SPI registers are loaded. When this is carried out, the Data Bytes are stored and updates to them are inhibited. The Checksum is then calculated on the Status Byte and these 4 Data Bytes. The Status Byte however can continue to be updated for a short time after the Checksum has been calculated. Therefore, when the Status Byte, 4 Data Bytes and the Checksum are loaded into the SPI register there is a chance that the Checksum is incorrect. It is therefore advised that if a Checksum Error is detected that the Status Byte should still be interrogated for the Status, such as BIT Fault.

How can I set the CRM102.1/CRM202.1 to their maximum (2700deg/s) range?

The measurement range of CRM102.1/CRM202.1 is three times that of CRM100/CRM200. The confusion arises because the CRM102.1 and CRM202.1 datasheets only document the 900deg/s range selection (the second highest range, equivalent to 300deg/s on the CRM100/CRM200). However, as noted on the web page, the CRM102.1/CRM202.1 gyros are capable of sensing up to 2700deg/s. To do this the rate range selection need to be set for the highest rate range for the device. By comparing their datasheets with those of the CRM100/CRM200, the method for achieving this can be deduced. In summary, in digital mode, set the Command Message bits 4 & 3 (RR1 and RR0) to ’00‘. In analogue mode, set pins SEL0 and SEL1 both to ground.

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