Analog circuits are at the heart of many electronic systems, providing accurate and precise signals for various applications. However, one of the challenges that design engineers face is dealing with noise and electromagnetic interference (EMI) in these circuits. These inconsistencies can disrupt the output signals, negatively affecting the pursuit of reliable, noise free circuits. In this article we will explore types of noise and discuss practical strategies to minimize their effects.
Sources and types of noise
Various factors contribute to noise in analog circuits, such as thermal noise, shot noise, flicker noise, and electromagnetic interference. Each type of noise affects different circuit components, and understanding these sources is crucial for effective noise mitigation.
Flicker noise, also known as 1/f noise, presents a low frequency phenomenon resulting from irregularities in the conduction path and bias currents within transistors. At higher frequencies, flicker noise is less noticeable because of the dominance of white noise, hence the “1/f” nomenclature. Although internal flicker noise cannot be controlled, system designers can minimize this effect by selecting the proper amplifiers for their application.
Shot noise, or Schottky noise, arises from imperfections in the conduction of charge carriers. As electrons encounter barriers (such as imperfections in metals), potential energy accumulates until the electron surmounts the barrier in a sudden “shot.” Shot noise is directly associated with current flow, so less current means more shot-noise voltage. By raising the current, the proportional impact is reduced, enhancing the signal-to-noise ratio.
Thermal noise is present in all circuit components, active or passive. Elevated temperature causes electron movement to intensify, which introduces a stochastic element to their motion that translates to noise. Thermal noise is like shot noise in that it has a Gaussian probability density distribution.
Techniques to reduce noise
There are multiple techniques that can be used to reduce noise, including the following:
Proper component selection: Choosing components with low noise figures and high immunity to interference is crucial for noise-sensitive designs. High-quality op-amps, voltage regulators, and precision resistors can contribute significantly to noise reduction. Look for op-amps with lower voltage noise density (nV/√Hz) and current noise density (PA/√Hz).
Incorporate bypass and filtering: Employ bypass capacitors at the power supply pins of the op-amp to reduce high-frequency noise from entering the amplifier. Additionally, incorporate passive filters (low-pass) at the input or output to reduce noise at unwanted frequencies.
Optimize grounding and layout: Proper grounding and layout techniques are crucial to minimize noise gathering. Separate the analog and digital ground planes, eliminate the ground loops, and keep high-current and noise-producing traces away from sensitive analog traces.
By optimizing grounding techniques, incorporating bypass and filtering, and selecting appropriate components, engineers can ensure that their analog circuits deliver accurate and reliable performance in the face of noisy environments. Apex Microtechnology offers a wide variety of low-noise amplifiers that meet the current and voltage requirements of various high-current and voltage industry applications.