Efficiently storing data for wide dynamic range and high resolution biological signals
Described herein are methods, devices and systems for efficiently storing data for sensed biological signals. A sensed biological signal, or an amplitude and/or filtered version thereof, is provided to an N-bit ADC of an IMD to produce an N-bit data value indicative of an amplitude of the biological signal at a point in time. One of a plurality of chords of a compression curve is selected, based on a magnitude of the N-bit data value, and used to produce an M-bit data value, which is a compressed version of the N-bit data value, wherein M<N. The M-bit data value is stored as an M-bit data slice within memory of the IMD, and can be expanded to a reproduced N-bit data value after being uploaded to a non-implanted device or system.
1 . For use by an implantable medical device (IMD), a method for efficiently storing data for a sensed biological signal, the method comprising:
providing the sensed biological signal, or an amplified and/or filtered version thereof, to an N-bit analog-to-digital converter (ADC) of the IMD, wherein N>8;
outputting, from the N-bit ADC of the IMD, an N-bit data value indicative of an amplitude of the sensed biological signal at a point in time;
selecting 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;
using 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, wherein M<N; and
storing 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, or the filtered and/or amplified version thereof, can be expanded to a reproduced N-bit data value after being uploaded to a non-implanted device or system.
2 . The method of claim 1 , further comprising:
storing a plurality of look up tables (LUTs) in registers or memory of the IMD, wherein each of the LUTs corresponds to a respective one of the plurality of chords of the compression curve;
wherein the selecting one of the plurality of chords of the compression curve, comprises selecting one of the plurality of LUTs based on which one of the plurality magnitude ranges the magnitude of the N-bit data value output from the ADC is within; and
wherein the using the selected one of the plurality of chords of the compression curve to produce the M-bit data value, comprises using the selected one of the plurality of LUTs to produce the M-bit data value.
3 . The method of claim 2 , wherein:
each LUT, of the plurality of LUTs, has a respective different output value for each of a plurality of different sub-ranges of magnitudes, such that the LUT is used to produce a same one of a plurality of different output values for a plurality of different input values that are within a same one of the sub-ranges of magnitudes.
4 . The method of claim 2 , further comprising:
updating one or more of the LUTs stored in the registers or memory to thereby modify how further N-bit data values that are output by the ADC are compressed to further M-bit data values that are stored in the memory.
5 . The method of claim 1 , further comprising:
repeating the outputting, the selecting, the using, and the storing for a plurality of additional N-bit data values indicative of amplitudes of the biological signal at a plurality of additional points in time, so that a plurality of M-bit data values, or filtered and/or amplified versions thereof, are stored as a plurality of M-bit data slices within the memory of the IMD.
6 . The method of claim 5 , wherein:
the selecting is performed using a plurality of magnitude comparators and a decoder that receives outputs of the magnitude comparators;
at any given time, each of the magnitude comparators compares a magnitude of a same one of the N-bit data values to a different one of a plurality of reference values that correspond to boundaries of the plurality of magnitude ranges; and
the decoder receives the outputs of the magnitude comparators and selects one of the plurality of chords by decoding the outputs of the magnitude comparators.
7 . The method of claim 5 , further comprising:
uploading the plurality of M-bit data values, or filtered and/or amplified versions thereof, that are stored in the memory of the IMD to a non-implanted device or system so that the M-bit data values, or filtered and/or amplified versions thereof, can be expanded to provide a plurality of N-bit reproduced data values, by the non-implanted device or system, and so that the N-bit reproduced values can be used by the non-implanted device or system to generate a reproduced version of the biological signal.
8 . The method of claim 1 , further comprising:
sensing the biological signal using a sensor or electrodes of, or communicatively coupled to, the IMD.
9 . The method of claim 1 , wherein:
16>N>8; and
M=8.
10 . The method of claim 1 , wherein the biological signal comprises one of:
an electrogram (EGM) signal indicative of cardiac electrical activity;
an electrocardiogram (ECG) signal indicative of cardiac electrical activity;
a plethysmography signal indicative of cardiac mechanical activity;
a signal indicative of pressure within a cardiac chamber;
a signal indicative of pressure within a body lumen;
a signal indicative of blood pressure;
a signal indicative of heart sounds;
a signal indicative of body temperature;
a signal indicative of motion; or
a cardiogenic impedance signal.
11 . The method of claim 1 , wherein the IMD comprises one of:
a pacemaker coupled to one or more transvenous leads;
a leadless pacemaker;
an insertable cardiac monitor (ICM); or
an implantable cardioverter defibrillator (ICD).
12 . 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.
13 . The IMD of claim 12 , further comprising:
memory or registers that store a plurality of look up tables (LUTs), wherein each of the LUTs corresponds to a respective one of the plurality of chords of the compression curve;
wherein the compressor is configured to select one of the plurality of chords of the compression curve by selecting one of the plurality of LUTs based on which one of the plurality magnitude ranges the magnitude of the N-bit data value output from the ADC is within; and
wherein the compressor is configured to use the selected one of the plurality of chords of the compression curve to produce the M-bit data value by using the selected one of the plurality of LUTs to produce the M-bit data value.
14 . The IMD of claim 13 , wherein:
each LUT, of the plurality of LUTs, has a respective different output value for each of a plurality of different sub-ranges of magnitudes, such that the LUT is used to produce a same one of a plurality of different output values for a plurality of different input values that are within a same one of the sub-ranges of magnitudes.
15 . The IMD of claim 13 , wherein:
in response to receiving instructions from a non-implantable device, the compressor is configured to update one or more of the LUTs stored in the registers or memory to thereby modify how N-bit data values that are output by the ADC are compressed to M-bit data values that are stored in the memory.
16 . The IMD of claim 12 , wherein:
the compressor comprises a plurality of magnitude comparators and a decoder that receives outputs of the magnitude comparators;
at any given time, each of the magnitude comparators compares a magnitude of a same one of the N-bit data values to a different one of a plurality of reference values that correspond to boundaries of a plurality of magnitude ranges; and
the decoder receives the outputs of the magnitude comparators and selects one of the plurality of chords of the compression curve by decoding the outputs of the magnitude comparators.
17 . The IMD of claim 12 , further comprising:
at least one of a digital filter and a digital amplifier, between the N-bit ADC and the compressor, configured to filter and/or amplify the N-bit data values output from the ADC before the N-bit data values are provided to the compressor.
18 . The IMD of claim 12 , wherein:
16 >N >8; and
M =8.
19 . The IMD of claim 12 , wherein the IMD comprises one of:
a pacemaker coupled to one or more transvenous leads;
a leadless pacemaker;
an insertable cardiac monitor (ICM); or
an implantable cardioverter defibrillator (ICD).