AC Coupling
Each channel can be selectively AC coupled. AC coupling causes the channel to only store the AC component of the signal. This process removes the DC component, leaving a signal who's mean is close to zero. The AC coupling is accomplished by using a finite impulse response (FIR) filter.
The AC coupling filter is a 7 Hz high-pass FIR filter designed through a least-squares algorithm and with a Hamming window applied. The number of filter taps (filter kernel width) is adjusted based on the sampling frequency to obtain a similar response curve for all sampling frequencies.
Frequencies less than 7 Hz (including the DC component) will be attenuated by this filter, and higher frequencies will not be affected.
DC attenuation is approximately -14 dB.
Passband ripple is less than 1%.
Examples of this filters affect and response for given sampling frequencies are displayed in the sections below.
500Hz Sampling Frequency