Eliminating Flicker Noise in Low Frequency Sensor Applications

What is Flicker Noise?

Flicker noise is a low-frequency phenomenon that is present within all electronics and is especially problematic in low-frequency data acquisition systems such as the outputs from strain gauges, pressure sensors, thermocouples, or any slow-moving sensor signal.

Operational Amplifiers

One key element within such a data acquisition system is the Operational Amplifier (op amp). While there are many different sources of noise within an op amp, flicker noise is perhaps the most mysterious and frustrating noise source with which a designer must contend. Flicker noise increases inversely with frequency, at a rate of 3 dB per octave, hence it is often referred to as 1/f noise (with “f” referring to frequency). This 1/f noise is still present at higher frequencies, but other noise sources within the op amp begin to dominate, negating the effects of 1/f noise. For most op amps, these other noise sources form a consistent white noise (meaning it is constant across frequency) floor across a majority of the frequency range, but the low frequency is still dominated by the 1/f noise.

This low-frequency noise can be very problematic if the input signal is also low frequency, as it becomes impossible to extract the signal of interest from the noise. So how does one deal with this dominating, low frequency noise? Attempting to filter out this noise without affecting the signal of interest is virtually impossible given the small bandwidth. Although a system designer cannot control or filter out the internal 1/f noise of an amplifier, the designer can minimize this noise source by selecting the proper amplifier for the application.

Zero-Drift Amplifiers

If 1/f noise is a big concern, then selecting a zero-drift amplifier is the best solution. The industry-standard term “zero-drift” refers to any amplifier that uses a continuously self-correcting architecture. The goal of zero-drift amplifiers is to minimize offset and offset drift. In the process, other DC characteristics such as Common mode and power supply rejection are also greatly improved. Another key benefit of these self-correcting architectures is that the 1/f noise is removed as part of the offset correction process. This noise source appears at the input and is relatively slow-moving, hence it appears to be a part of the amplifiers offset and gets compensated accordingly. This results in an amplifier with a flat noise floor that extends all the way to DC, enabling significantly improved measurement accuracy at low frequency.

Flicker or 1/f noise is a physical phenomenon that affects all electronics, including op amps. However, this noise source doesn’t have to be a limitation in low frequency data acquisition systems. In addition to providing superior DC performance, such as low initial offset and low offset drift, zero-drift amplifiers also have the added advantage of eliminating 1/f noise, which is critical for low frequency applications. Microchip’s wide portfolio of zero-drift op amps provides flexible data acquisition solutions for a wide variety of end applications. With multiple price and performance levels from which to choose, Microchip enables high-performance data acquisition, even within cost-sensitive applications.

Please visit the op amp page to learn more about Microchip’s line of op amps, including zero-drift amplifiers.

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