Author: Kristijan Saklamaev
Mentor: assoc. prof. dr. Matej Rojc
Co-mentor: assoc. prof. dr. Anton Pleteršek
External Co-mentor: dr. Matija Podhraški
Program: Level 2 study, Electrical Engineering, course Electronics
Date: August, 2022
DKUM: KRISTIJAN SAKLAMAEV
Introduction
The master’s thesis deals with the interpolation of signals of several types of AMR sensors, which are used in today’s industry in various applications. AMR sensors are contact-less devices that sense and measure the direction of a magnetic field, which can be used to detect position and rotation. In the master’s thesis, we present the principle of operation of AMR sensors, a comparison of different versions of AMR sensors and a comparative analysis with other types of magnetic sensors. We provide an explanation and example of many effects on the measurement accuracy in a functional system (offset, temperature, hysteresis, amplitude, gain, etc.). A sensor can be a passive element or an active electronic device that generates an output signal, when a physical phenomenon is detected. When the sensor detects a change in the environment, it sends a digital or analog signal to the other circuit components. Today, there are several types of sensors available on the market from different manufacturers, each with its own advantages and disadvantages. Among the most common types are optical sensors, temperature sensors, magnetic sensors, tactile sensors, etc. In this part, we focus on magnetic sensors or sensors that detect the presence of a magnetic field. There are many different types of magnetic sensors, a typical one being the Hall sensor, which is based on the effect of the Lorentz force on an electric current in the presence of a magnetic field. The greatest advantage of magnetic sensors is their ability to operate in demanding environments, while maintaining a high degree of accuracy. This means that magnetic sensors do not require physical contact to work effectively, which is one of the many advantages of these types of sensors. Magnetic sensors are often used as part of systems that detect position and angle of rotation. we discuss various magnetoresistive phenomena, such as GMR, TMR and others. The focus is on the AMR phenomenon, as well as on sensors based on this phenomenon. We analyzed a typical AMR sensor SM2L, as well as some development samples from RLS company. In order to analyze the impact of various factors on the error, a series of measurements were carried out to confirm the expected impacts.
Position encoders and their use for applications
An encoder is a device that converts data from one format to another. The encoder detects mechanical movements and converts them into an analog or digitally coded output signal for detecting position. Velocity, acceleration and direction can be derived from the position in linear or rotational motion. There are different types of encoders, which can be distinguished according to the principle of operation, purpose or complexity. An MR (magnetoresistive) sensor consists of a resistor formed from a magnetically sensitive alloy, such as nickel-iron (NiFe). The magnetic domains in NiFe are stressed by an external magnetic field, which reduces the resistivity of the material. The resistance then quickly normalizes, when the field is removed, making it a useful tool for measuring magnetic fields (in applications, such as: reading from hard drives). The MR encoder consists of a housing with a series of lithographically formed thin-film resistors and an IC circuit mounted on the shaft of a motor with alternating magnetic domains.
Different ways of interpolating AMR sensor signals
Drive controllers today require high-resolution magnetic or optical position sensors for speed control or detecting position, which requires the use of special integrated circuits for sensor signal conditioning, and sine/cosine-to-digital conversion. We analyzed the methods and problems of “interpolation” using sine/cosine-to-digital conversion (A/D conversion), measurement errors associated with sensors, and how to compensate them, and presented the latest semiconductor solutions and their selection. Interpolation is responsible for non-linear A/D conversion (due to physical irregularity) of sine/cosine signals into angular steps, which are displayed incrementally as a quadrature signal or as an absolute data word, representing the phase of the sine angle signal.
Interpolator design, SOC analysis and development
A reference block with precisely defined characteristics is one of the most critical building blocks in high-performance circuits. Since these circuits contain a large number of passive and active components, their operation must not be affected process, supply voltage or temperature fluctuations (PVT – Process, Voltage, Temperature). Devices that are not sensitive to PVT variations can be used in different environments and in different applications. The reference block presented can be found in every integrated electronic device (SoC). When we talk about a reference block, we mean a circuit that, regardless of supply voltage or temperature fluctuations, outputs a stable or precisely determined reference voltage or current. The voltage reference is used as an input in analog-digital converters, comparators or various amplifiers, which – in our case – are also all components of the mentioned interpolator. A good voltage reference is important for the interpolator, as it ensures the stabilization of the interpolator parameters.
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