Efficiently storing data for wide dynamic range and high resolution biological signals

An implantable medical device (IMD), comprising:

• an N-bit analog-to-digital converter (ADC) that is configured to receive a sensed biological signal, or an amplified and/or filtered version thereof, and output N-bit data values indicative of an amplitude of the biological signal at each of a plurality of points in time, wherein N >8;
• and
• a compressor configured to compress the N-bit data values to respective M-bit data values, wherein M <N, so that data for the biological signal can be stored as M-bit data slices within memory of the IMD;
• wherein for each of the N-bit data values the compressor is configured to
• select one of a plurality of chords of a compression curve based on which one of a plurality magnitude ranges a magnitude of the N-bit data value output from the ADC is within;
• use the selected one of the plurality of chords of the compression curve to produce an M-bit data value, which is a compressed version of the N-bit data value output from the ADC;
• and
• store the M-bit data value, or a filtered and/or amplified version thereof, as an M-bit data slice within memory of the IMD, so that the M-bit data value can be expanded to a reproduced N-bit data value after being uploaded to a non-implanted device or system.