Anti-aliasing Filter Design

Last modified by Microchip on 2024/10/08 13:54

The Anti Aliasing Filter Design helps you design a low-pass filter for use with an Analog-to-Digital Converter (ADC). The tool will prompt you for the bandwidth of the signal and the sampling frequency, the resolution, and the Signal-to-Noise Ratio (SNR) of the ADC. The passband frequency determines the bandwidth of the Anti-Aliasing Filter (AAF). The frequency range is limited to values from 0.1 Hz to 1 MHz.

Anti Aliasing Filter Design

Enter the sampling frequency of the A/D converter. Due to the Nyquist Theorem, the sampling frequency must be greater than two times the bandwidth of the signal of interest. However, we recommend doing more than that, like 5-10 times the bandwidth of the signal of interest.

sampling frequency

Enter the resolution of the ADC. The resolution must be between 8 bits and 24 bits.

ADC resolution

Enter the desired SNR. SNR is calculated using the equation:

𝑆𝑁𝑅 = 6.02β‹…π΄π·πΆπ‘…π‘’π‘ π‘œπ‘™π‘’π‘‘π‘–π‘œπ‘› + 1.76

Decreasing the desired SNR value will decrease the order of the filter while increasing SNR will increase the filter order.

SNR

On this page, you can change the resistor and capacitor component tolerances, power supply voltages, voltage ratio gain, and topology.

Choosing to minimize the bill of materials will cause the filter design tool to use the same op amp in every stage of the filter. The filter design tool will pick the op amp with the highest gain-bandwidth product of each of the filter stages and use that for every stage. Note, however, that op amps with higher gain-bandwidth products tend to have higher power consumption. Choosing to minimize power consumption will allow for different op amps in each stage, thus reducing the overall power consumption.

resistor capacitor tolerances

The completion page summarizes the selections and presents the filter options.

While it is possible to create a filter of any order, FilterLab will only design a filter of up to eight orders. If the requirements set by the Filter Design Aid need a higher order than eight for a particular type, it will not show up in the results. For example, if the design requirements necessitate a 10th order Butterworth filter, a 10th order Bessel filter, or an 8th order Chebychev filter, only the Chebychev filter option will be available to select.

selection summaries

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