ADIS16060

Rev. 0 | Page 9 of 12

THEORY OF OPERATION

The ADIS16060 operates on the principle of a resonator

gyroscope. Two polysilicon sensing structures each contain a

dither frame that is electrostatically driven to resonance. This

generates the necessary velocity element to produce a Coriolis

force while rotating. 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 rate

signal is then converted to a digital representation of the output

on the SPI pins. The dual-sensor design provides linear acceleration

(vibration, shock) rejection. 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.

Because only 5 V is typically available in most applications, a charge

pump is included on chip. After the demodulation stage, a single-

pole, low-pass filter on the chip is used to limit high frequency

artifacts before final amplification. The frequency response is

dominated by the second low-pass filter, which is set by adding

capacitance across RATE and FILT.

ANALOG-TO-DIGITAL CONVERTER INPUT

Figure 12 shows an equivalent circuit of the input structure of

the ADIS16060 auxiliary ADC.

The two diodes, D1 and D2, provide ESD protection for the analog

inputs, AINx (AIN1 and AIN2). Care must be taken to ensure

that the analog input signal does not exceed the supply rails by

more than 0.3 V, because exceeding this level causes these diodes to

become forward-biased and to start conducting current. However,

these diodes can handle a forward-biased current of 130 mA

maximum. For instance, these conditions may eventually occur

D1

D2

AINx

GND

VDD

Figure 12. Equivalent Analog Input Circuit

During the acquisition phase, the impedance model for AINx is a

made up of some serial resistors and the on resistance of the

ADC sampling capacitor.

During the conversion phase, when the switches are open, the

low-pass filter that reduces undesirable aliasing effects and

limits the noise.

When the source impedance of the driving circuit is low, the

ADC input can be driven directly. Large source impedances

significantly affect the ac performance, especially THD. The dc

performances are less sensitive to the input impedance.

RATE SENSITIVE AXIS

1

4 5

8

LONGITUDINAL

AXIS

RATE

AXIS

POSITIVE

MEASUREMENT

DIRECTION

LATERAL

AXIS

Figure 13. Rate Signal Increases with Clockwise Rotation