ADXRS300

Rev. B | Page 6 of 8

THEORY OF OPERATION

The ADXRS300 operates on the principle of a resonator gyro.

Two polysilicon sensing structures each contain a dither frame,

which is electrostatically driven to resonance. This produces the

necessary velocity element to produce a Coriolis force during

angular rate. At two of the outer extremes of each frame,

orthogonal to the dither motion, are movable fingers that are

placed between fixed pickoff fingers to form a capacitive pickoff

structure that senses Coriolis motion. The resulting signal is fed

to a series of gain and demodulation stages that produce the

electrical rate signal output. The dual-sensor design rejects

external g-forces and vibration. Fabricating the sensor with the

signal conditioning electronics preserves signal integrity in

noisy environments.

The electrostatic resonator requires 14 V to 16 V for operation.

Since only 5 V is typically available in most applications, a

charge pump is included on-chip. If an external 14 V to 16 V

supply is available, the two capacitors on CP1–CP4 can be

omitted and this supply can be connected to CP5 (Pin 7D) with

a 100 nF decoupling capacitor in place of the 47 nF.

After the demodulation stage, there is a single-pole low-pass

external user-supplied capacitor (CMID). A CMID capacitor of

100 nF sets a 400 Hz ±3 5% low-pass pole and is used to limit

high frequency artifacts before final amplification. The band-

and the Setting Bandwidth section).

AGND

TEMP

ST2

ST1

CP1

CP2

RATEOUT

CP4

PDD

CMID

SUMJ

2.5V

6A

5A

4A

3A

2A

1B

1C

1D

1E

1F

7B

7C

7D

7E

7F

6G

5G

4G

3G

2G

CP5

CP3

100nF

22nF

AVCC

100nF

100nF

PGND

22nF

47nF

5V

NOTE THAT INNER ROWS/COLUMNS OF PINS HAVE BEEN OMITTED

FOR CLARITY BUT SHOULD BE CONNECTED IN THE APPLICATION.

Figure 4. Example Application Circuit (Top View)

SUPPLY AND COMMON CONSIDERATIONS

Only power supplies used for supplying analog circuits are

recommended for powering the ADXRS300. High frequency

noise and transients associated with digital circuit supplies may

have adverse effects on device operation.

Figure 4 shows the recommended connections for the ADXRS300

where both AVCC and PDD have a separate decoupling capacitor.

These should be placed as close to the their respective pins as

possible before routing to the system analog supply. This mini-

mizes the noise injected by the charge pump that uses the PDD

supply.

It is also recommended to place the charge pump capacitors

connected to the CP1–CP4 pins as close to the part as possible.

These capacitors are used to produce the on-chip high voltage

supply switched at the dither frequency at approximately

14 kHz. Care should be taken to ensure that there is no more

than 50 pF of stray capacitance between CP1–CP4 and ground.

Surface-mount chip capacitors are suitable as long as they are

rated for over 15 V.

5V

+

–

SELF

TEST

AVCC

ST1

ST2

3A

5G

4G

ADXRS300

CP2

CP1

PDD

4A 5A

7E

6G

CHARGE

PUMP/REG.

12V

PTAT

7F

6A

7B 7C

7D

47nF

CP4 CP3 CP5

RATE

SENSOR

2G

1F

1D

CORIOLIS

SIGNAL CHANNEL

AGND

CMID

1C

SUMJ

RATE-

OUT

2.5V

1B

2A

1E

3G TEMP

180k

Ω 1%

RESONATOR LOOP

DEMOD

π

2.5V REF

≈7kΩ±35%

100nF

22nF

100nF

100nF

22nF

PGND

Figure 5. Block Diagram with External Components