User guide
PNIASIC
TheoryofOperation
Theory of Operation
The PNI ASIC contains the entire measurement circuitry necessary to use PNI Corporation’s magneto-
inductive sensors as well as bus interface circuitry. Communication between the PNI ASIC and the host
microprocessor is over SPI bus interface. After being reset a single 8 bit command from the host system
configures and initiates an axis sample from the ASIC. The ASIC can be used to interface from one to
three sensors depending on application requirements, unused sensor connections should remain floating.
The interface and functional sequence is as follows: A reset pulse is sent to clear the counter of previous
sample reading and reset the DRDY line low. The command byte is sent which selects the axis to sample
and the resolution. Upon receiving the command byte the high speed clock turns on and the sample
sequence begins. Forward and reverse sampling is done automatically within the ASIC, upon completion
the DRDY output will go high indicating that the 16 bit 2’s compliment data is available to be clocked out
and the high speed clock is turned off returning the AISC to idle mode to reduce power consumption.
Figure 1: ASIC Block Diagram
The PNI Corporation’s magneto-inductive sensor changes its inductance with a change in magnetic field
parallel to the sensor. The ASIC sensor output reading is defined as the difference between a forward and
a reverse biased sensor measurement. To make a measurement, the sensor is switched into an L/R
oscillator circuit. One side of the sensor is grounded while the other side is alternately driven with
positive and negative current through the oscillator. The PNI ASIC will then switch the bias connection to
the sensor and make another measurement. The side that was previously grounded is now charged and
discharged while the other is now grounded.
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