Introduction

Rotary encoders are electro-mechanical devices that convert angular motion into digital signals. The encoder consists of a rotor disc with defined segments and a stationary part with sensors that detect the movement of rotor disc segments. As the rotor disc rotates, the sensors generate pulses which are decoded into position and motion data.

Rotary encoder ICs (integrated circuits) take the pulse outputs from the encoder hardware and convert them into usable information. Encoder decoder ICs process the pulses to determine direction of rotation, count the pulses to calculate position, and output clean digital waveforms. They simplify the pulse decoding logic and provide robust performance for industrial controls, automation equipment, robotics, and other applications requiring rotational sensing.

This article provides an overview of common rotary encoder decoder ICs, their key features and specifications, and guidance on selecting the right option for your application.

How Rotary Encoder Decoder ICs Work

Rotary encoders generate digital pulses as their shaft rotates. The frequency and pattern of pulses depends on factors like encoder resolution, shaft speed, and sensing method (optical, magnetic, mechanical contact).

Decoder ICs process these pulses using digital logic gates and counters. Key functions include:

• Pulse shaping – Cleans up the raw encoder pulses into crisp digital waveforms
• Quadrature decoding – Determines direction from two pulse trains with 90° phase difference
• Pulse counting – Counts pulses to calculate angular position
• Index pulse handling – Resets counter on reference index pulse
• Output formatting – Converts position data to usable interfaces like SPI, UART, PWM

This converts messy real-world pulses into clean positional feedback. Some encoders have an index (reference) pulse to establish an absolute zero position reference.

Below is a simple block diagram of a typical rotary encoder decoder IC:

Block diagram of a typical rotary encoder interface IC – Image source: ResearchGate

Advanced decoder ICs integrate additional features like programmable filtering, error checking, self-diagnostics, interpolation for high resolution, and support for advanced communication protocols.

Key Specifications

Key specifications and parameters to consider when selecting a rotary encoder decoder IC:

• Channels – Number of encoder inputs supported
• Resolution – Maximum encoder pulse count per revolution
• Quadrature decoding – Supports A/B phase shifted pulse decoding
• Index pulse – Handles reference index pulse for absolute position
• Pulse frequency – Maximum input pulse rate
• Output interfaces – SPI, UART, PWM, Up/Down count, etc.
• Voltage – Input and supply voltage range
• Package – Size and pin configuration

Matching the IC to your encoder resolution, pulse rate, and interface requirements ensures proper functionality.

Top Rotary Encoder Decoder ICs

Here are some popular encoder decoder ICs to consider:

1. AS5040

• 10-bit magnetic rotary encoder decoder
• SPI and PWM output
• Up to 2048 PPR resolution
• Index and programmable error checking
• 2.5V to 5.5V supply
• SOIC-8 package

2. AS5048A

• 14-bit magnetic rotary encoder decoder
• BiSS, SSI, and PWM output
• 16384 PPR resolution
• 1LSB accuracy
• 1.71V to 3.6V supply
• SSOP-16 package

3. AM4096

• 12-bit optical rotary encoder decoder
• SPI & BiSS C output
• Up to 4096 PPR resolution
• Index and programmable filtering
• 2.7V to 3.6V supply
• TSSOP-14 package

4. AEAT-6012-A06

• 12-bit optical rotary encoder decoder
• Direction and clock outputs
• 4096 PPR resolution
• Index and programmable filtering
• 2.7V to 5.5V supply
• SOIC-8 package

5. MAE3RA Series

• 10/12/14-bit incremental encoder ICs
• Quadrant decoding, interpolation
• SPI, ABZ, UVW output
• 4096 to 16384 PPR
• Automotive grade
• TSSOP-14/16 packages

This covers some of the most versatile encoder decoder ICs for different resolutions, supply voltages, and output interfaces. Check datasheets for full specifications and capabilities.

Guidance on Selecting an Encoder Decoder IC

Follow these steps to select the right rotary encoder decoder IC for your application:

1. Determine required resolution – Match the IC to your encoder’s pulses per revolution (PPR).
   • More PPR needs a higher count decoder IC.
   • Lower resolution encoders can use simple decoders.
2. Check maximum pulse frequency – Ensure the IC can handle the encoder’s maximum pulse rate. High speed encoders need decoders rated for fast pulse rates.
3. Identify interface needs – SPI, UART, PWM, Up/Down Counter – Choose an IC with your required output signal(s).
4. Consider index pulse – Index pulse allows for absolute positioning. Select an IC that can process the index signal if required.
5. Evaluate advanced features – Programmable filters, diagnostics, interpolation, error checking, etc can simplify system integration.
6. Check voltage ranges – IC supply voltage and input thresholds must match your system and encoder output levels.
7. ** Review packaging** – SOP, SSOP, and TSSOP packages are common. Some offer wettable flanks and other benefits. Pick one that suits your PCB design.
8. Optimize cost – Balance required performance against IC cost to avoid over-engineering.

Matching the decoder IC capabilities to your specific rotary encoder ensures reliable performance. Check multiple datasheets and use parametric search tools to find your ideal encoder interface solution.

Example Implementations

Here are a few examples of how rotary encoder decoder ICs are implemented:

Motor Position and Speed Control

• Optical incremental encoder on motor shaft provides speed and position feedback
• AS5048A decoder IC converts encoder pulses into a 14-bit position value via SPI
• Microcontroller uses position data to precisely control motor speed and position in a closed loop

Robot Joint Angle Measurement

• 10-bit magnetic absolute encoder senses joint angle
• MA3-10ART IC decodes angle into 10-bit SPI output
• Absolute angle eliminates risk of loss of position on power down
• MCU monitors joint angle for precise robotic motion control

CNC Machine Axis Position

• High resolution incremental encoder with index pulse installed on machine axis
• AM4096 IC decodes A/B pulses for 12-bit resolution position data
• Index pulse resets absolute position reference
• BiSS-C output connects to motion controller for precision axis control

Automotive Steering Angle Sensor

• Contactless magnetic rotary encoder senses steering column angle
• MAE3RA31A1U IC provides 14-bit resolution with 16x interpolation
• Independent power supply lines for functional safety
• Automotive-grade ASIL qualified encoder system

These examples demonstrate the flexibility of encoder decoder ICs across position sensing applications.

FAQs

What is the difference between incremental and absolute rotary encoders?

Incremental encoders provide relative angular position based on counting pulses. Position is lost when power is removed. Absolute encoders use coded tracks to maintain position power down. Some absolute encoders simulate incremental outputs.

How do you determine encoder resolution?

Resolution is specified in pulses per revolution (PPR). More pulses equals higher resolution. Common values range from 32 PPR to 4096 PPR or even higher. Match your encoder PPR to an appropriate decoder IC.

What signals do incremental encoders output?

Most incremental encoders output two pulse trains in quadrature (90° phase shifted) labeled A and B. Some also have a third Index or Z pulse to indicate a reference position.

What causes noisy pulses from a rotary encoder?

Electrical noise, loose mechanical components, damaged encoder wheels, improper grounding, and environmental contamination can cause erratic encoder pulses. Proper installation, filtering, and shielding improves signal integrity.

How do you electrically connect a decoder IC to an encoder?

Check the encoder datasheet for pinout and signal diagrams. Typically encoders have power, ground, A channel output, B channel output, and sometimes index/Z output. Route these signals to the corresponding pins on the decoder IC based on its pinout.

Conclusion

Rotary encoder decoder ICs translate angular motion into usable digital position and motion data. Choosing the right decoder involves matching resolution, speed, output signals, and other parameters between the encoder and IC. Popular options from suppliers like ams, CUI Devices, Melexis, and Microchip offer a range of capabilities to suit industrial, automotive, consumer, and other rotary encoder applications. The decoder IC simplifies and enhances utilization of position information from optical or magnetic encoders.