ADIS16120

Rev. A | Page 8 of 12

THEORY OF OPERATION

The base sensor in the ADIS16120 operates on the principle of

a resonator gyroscope. Two polysilicon sensing structures each

contain a dither frame that is electrostatically driven to reso-

nance. This produces the necessary velocity element that creates

a Coriolis force during angular motion. At the two outer extremes

of each frame, orthogonal to the dither motion, are movable

fingers that are placed between fixed fingers to form a capaci-

tive pickoff structure that senses Coriolis acceleration. The

resulting signal is fed to a series of gain and demodulation

stages that produce the representative rate signal output. One

advantage of the core dual-sensor design approach is that it

provides improved rejection of external g-forces and vibration.

The ADIS16120 signal conditioning circuit provides an

optimized filtering network that controls the resonators

influence on noise while supporting a nominal bandwidth

of 320 Hz. Another feature that helps reduce sensitivity to

power supply noise is the integration of approximately 1.8 μF

of decoupling capacitance inside the ADIS16120.

The offset and sensitivity performance is factory calibrated and

the internal reference voltage used in this calibration process is

offered for external use. A temperature sensor is also provided

for system level use, where appropriate.

SETTING THE BANDWIDTH

An important trade-off in angular rate measurement applica-

tions is the one between total system noise and bandwidth. The

ADIS16120 offers the flexibility to optimize this trade-off at the

system level. The signal processing circuit of the ADIS16120

provides a three-pole, low-pass filter, as shown in Figure 14.

LPF

180kΩ

180kΩ

820pF

FILTER

RATEOUT

OUTPUT

BUFFER

F1 = 400Hz

±35%

LPF

F2 = 1kHz

±10%

F3 = 1kHz

±10%

Figure 14. Simplified Filtering Network

The bandwidth of the third stage can be reduced by installing a

single capacitor across the RATEOUT and FILTER pins. Figure 15

provides a relationship for selecting the appropriate capacitor

value and Table 5 provides bandwidth estimates for standard

capacitor values.

The initial bandwidth of the ADIS16120 is dominated by the first

stage and is dependent on the process variation of the base sensor.

By reducing the bandwidth of the third filter stage, the influence of

the first stage is reduced, and tighter bandwidth tolerances can be

achieved.

1000

100

10

1

0.1

0.01

0.001

100

100M

10M

1M

100k

10k

1k

CAPACITANCE (pF)

Figure 15. Bandwidth vs. Capacitance

Table 5. Nominal Bandwidth for Standard Capacitor Values

C (pF)

BW (Hz)

C (pF)

BW (Hz)

1000

267.3

10,000

78.4

1200

256.2

12,000

67.1

1500

244.1

15,000

55.2

1800

225.5

18,000

46.4

2200

211.9

22,000

38.8

2700

192.3

27,000

31.8

3300

173.2

33,000

26.2

3900

156.4

39,000

22.2

4300

148.9

43,000

20.2

4700

140.4

47,000

18.5

5100

132.9

51,000

17.1

5600

124.5

56,000

15.6

6200

115.6

62,000

14.1

7500

99.0

75,000

11.7

8200

92.7

82,000

10.7

9100

85.5

91,000

9.6

SELF-TEST FUNCTION

The ADIS16120 provides a self-test function that exercises the

mechanical structure of the sensor. To use this function, Pin 1 to

Pin 7 and Pin 9 must be tied together and driven to a high logic

state to activate this function. A continuous self-test does not

damage the device.