In ASK decoding, a narrow band lowpass filter is used to estimate the amplitude of carrier so the decision threshold can be set to the average carrier amplitude. In integer arithmetic digital filter, When signal is numerically small or the bandwidth of a filter is narrow, quantization error become severe. But how severe? Some Matlab simulation is carried out to demonstrate the effect of quantization error on small number and different bandwidth of lowpass filter.
Small input
Final filter output is very departed from the expected value
Larger input
Final filter output is less departed from the expected value
Even larger input
Final filter output is quite close to the expected value
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