ADXRS401

Rev. 0 | Page 9 of 12

SETTING BANDWIDTH

with on-chip resistors to create two low-pass filters to limit the

bandwidth of the ADXRS401’s rate response. The –3 dB

(

)

OUT

OUT

OUT

C

R

π

2

1/

f

×

×

×

=

trimmed during manufacturing to be 180 kΩ ±1%. Any external

resistor applied between the RATEOUT (1B, 2A) and SUMJ

(1C, 2C) pins will result in:

() (

EXT

EXT

OUT

R

kΩ

180

/

R

kΩ

180

R

+

×

=

)

The −3 dB frequency is set by RSEN (the parallel combination

rate sensitivity during manufacturing and have a ±35%

tolerance. Its primary purpose is to limit the high frequency

demodulation artifacts from saturating the final amplifier stage.

Thus, this pole of nominally 400 Hz @ 0.1 µF need not be

precise. Lower frequency is preferable, but its variability usually

requires it to be about 10 times greater (in order to preserve

phase integrity) than the well-controlled output pole. In general,

both −3 dB filter frequencies should be set as low as possible to

reduce the amplitude of these high frequency artifacts, as well as

to reduce the overall system noise.

INCREASING MEASUREMENT RANGE

To increase the full-scale measurement range of the ADXRS401,

place an external resistor between the RATEOUT (1B, 2A) and

is factory-trimmed to 180 kΩ.

For example, a 330 kΩ external resistor gives approximately

10mV/°/sec sensitivity and a commensurate ∼50% increase in

the full-scale range. This is effective for up to a 4× increase in

the full-scale range. (The minimum value of the parallel resistor

allowed is 45 kΩ.) Beyond this amount of external sensitivity

reduction, the internal circuitry headroom requirements

prevent further increase in the linear full-scale output range.

The drawbacks of modifying the full-scale range are the

additional output null drift (as much as 2°/sec over

temperature) and the readjustment of the initial null bias. See

Null Adjust section and Application Note AN-625 for details.

TEMPERATURE OUTPUT AND CALIBRATION

It is common practice to temperature-calibrate gyros to

improve their overall accuracy. The ADXRS401 has a

temperature-proportional voltage output that provides input to

such a calibration method. The voltage at TEMP (3F, 3G) is

nominally 2.5 V at 27°C and has a PTAT (proportional to

absolute temperature) characteristic of 8.4 mV/°C. Note that the

TEMP output circuitry is limited to 50 µA source current.

Limiting the bandwidth of the device reduces the flat-band

noise during the calibration process, improving the

measurement accuracy at each calibration point.

5G

4G

3A

5V

2G

1F

7F

6A

7D

7C

7B

1C

4A

5A

7E

6G

1D

2A

1E

3G

1B

PDD

12V

+

ADXRS401

1

µF

22nF

100nF

22nF

CP2

CP1

PGND

CP4

CP3

CP5

CHARGE PUMP/REG.

TEMP

PTAT

RATE-

OUT

2.5V

π

DEMOD

RATE

SENSOR

SELF

TEST

100nF

100nF

CMID

AGND

AVCC

ST1

ST2

CORIOLIS SIGNAL CHANNEL

180k

Ω 1%

SUMJ

2.5V REF

RESONATOR LOOP

–

Figure 15. Block Diagram with External Components