The Study on 24 Bits ADC's Acquisition Dynamic Range Extension Method

The seismic signal’s amplitude span is very large, the dynamic range of the observed signal even more than 160dB, so the broadband seismometer output dynamic range should be above 150dB. However, the 24 bits acquisition units usually used, which based on ΣΔ Analog to Digital chip, the dynamic range is just around 130dB. As a result, the acquisition unit can’t resolve the useful signal from tiny earthquake, and when the big earthquake happened, the acquisition unit shows amplitude limiting phenomena. In this paper, we will introduce a method which using two 24 bits ADCs in acquisition unit to extend the dynamic range. That means using one ADC with higher resolution to acquire small signal, and using one ADC with lower resolution to acquire large signal, get the full record of the data. In the end, we combine two acquired data as one 32 bits conversion data. After testing, the dynamic range of experimental prototype used this method reached 155dB＠50SPS.