Method and apparatus for increasing the low frequency dynamic range of a system for measuring physiological signals with an implantable medical device

Abstract

A signal measuring system for use with an Implantable Medical Device (IMD) is provided for measuring physiologic signals having a relatively large effective dynamic range. In one embodiment, the system includes a High-Pass Filter (HPF), an Analog-to-Digital Converter (ADC), a Decimation Filter (DF), and a Compensation Filter (CF). The HPF receives an input signal that includes both the baseline wander imposed on a physiological signal. According to one aspect of the invention, the HPF attenuates low frequency components of the input signal, including a portion of the frequency band within the desired output signal bandwidth. The ADC then oversamples the output signal of the HPF. The DF receives the output samples from the ADC and generates output samples at rate that is at least twice the maximum frequency of the desired output signal. The CF then amplifies the low frequency end of the DF output samples. The gain and cutoff frequency of the CF are selected to offset the HPF attenuation of those low frequency components of the input signal below the cutoff frequency of the HPF and above the minimum frequency of the desired output signal. In one embodiment, the DF and CF are implemented by a processing circuit executing programmed instructions. The processing circuit may be included within the IMD, or may be partially or fully implemented within a device that is external to the IMD.