Inductive encoders are an emerging trend in industrial position sensing applications due to the inherent immunity to external stray magnetic fields, low cost, and relatively high resolution. While mechanical resolvers are immune to external stray magnetic fields, PCB-based inductive angle sensors offer lower system cost, operate at lower power, offer higher accuracy, and built-in digital processing with a high EMC immunity bidirectional digital interface to the industrial drive.

Inductive sense technology typically requires a target board and a coil board. The conductive target board can be a pattern printed on a PCB, while the coil board contains both receiver and excitation coils. The coil PCB is stationary, while the target PCB is mounted to the motor shaft and rotates. The excitation coil generates a secondary voltage on the receiver coils depending on the position of the target relative to the receiver coils. A signal representation of the position is obtained by reading in and processing the voltages from the receiver coils, and giving analog outputs representing the sine and cosine components of the position of the target.

As Figure 2-1 shows, the inductive encoder typically uses multipole pair receiver coils to get a higher resolution, but this indicator only provides incremental position. Nonius encoding is a method to get absolute position, Nonius encoding requires two sets of receiver coils with coprime periods.

The electrical signal chain offset and gain as well as sample rate, speed, and resolution of the ADC impact the angle accuracy. Components with very low temperature drift help reduce the angle error. Decoding of the angle from the sine and cosine sensor signals require math functions such as division, multiply-and-accumulate, and arctangent.

Small footprint circuits with high integration and low power consumption are critical to design the smallest form factor circular PCBs. Since the encoder can be motor integrated, ambient operating temperatures at least up to 125°C are typically required.