US007474247B1
(12) Unlted States Patent
(10) Patent N0.2
Heinks et al.
(54)
(75)
US 7,474,247 B1
(45) Date of Patent:
7,053,807 B1
7,079,061 B2
Jan. 6, 2009
DETECTING OVERLOADING OF AN
ANALOG-TO-DIGITAL CONVERTER OF AN
IMPLANTABLE MEDICAL DEVICE
7,102,558 B2
5/2006 Gaalaas
7/2006 Schuurmans
9/2006 Dev31
Inventors: Michael W. Heinks, New Brighton, MN
(US); Joel A. Anderson, Brooklyn Park,
MN (US); Wenxiao Tan, Murphy, TX
7’l42’143 B2
7,176,817 B2
7,221,303 B1
11/2006 Draxelmayr
2/2007 Jensen
5/2007 Melanson
(Us)
(73) Assignee: Medtronic, Inc., Minneapolis, MN (US)
( * ) Notice:
Subject to any disclaimer, the term of this
(
patent is extended or adjusted under 35
Continued
)
OTHER PUBLICATIONS
U.S.C. 154(b) by 0 days.
US. Appl. No. 11/861,856, ?led Sep. 26, 2007 entitled “Capacitive
(21) Appl. No.: 11/861,945
Digital-to-Analog Converter Reset inanImplantable Medical Device
Analog-to-Digital Converter” reference No. P0028398.00.
(22) Filed:
Sep. 26, 2007
(Continued)
(51)
Int. Cl.
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(52)
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58
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Primary ExammeriKhai M Nguyen
us. Cl. ..................................... .. 341/155- 341/143
F' 1d fCl
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341/155,
(74)A”0r”@y~4g@”’10rFirm*Mi°hae1C-S°1dner
(57)
ABSTRACT
See application ?le for complete search history.
(56)
References Cited
In general, this disclosure is related to detecting overload
Within an analog-to-digital converter (ADC) of an implant
able medical device (IMD). The IMD may include an over
U.S. PATENT DOCUMENTS
‘SL233’?
:
; $503121
load detection module that determines Whether the ADC is
5’329’28 l A
5,606,320 A
7/1994 B all;gam'l eI et a1‘
2/1997 Kleks
5,742,246 A *
4/1998 Kuo et al. ................. .. 341/143
i
operating in an overload condition. When the overload detec
tion module determines the ADC is operating in the overload
Erone et 31'
condition for a particular period of time, the ADC may send
an overload signal to a processor that processes the output of
6’354’299 B1 *
3/2002 P22712111 et al
128/899
the ADC. The overload signal noti?es the processor that the
633623763 B1
6,389,315 B1*
3/2002 Wang
' iiiiiiiiiiii "
5/2002 Schu etal. .................. .. 607/16
ADC is operating in or is close to operating in the overload
condition. In response to the indication from the ADC, the
processor of the IMD may disregard the output of the ADC.
6,535,153 B1
3/2003 Zierhofer
6,556,859 B1 *
4/ 2003 wohlgemu?l et 31 ----- -- 600/509
The processor may continue to disregard the output of the
6,567,025 B2
5/2003 sehreler et a1~
ADC until the overload signal is deactivated, thereby indicat
gggg’;
,
x1111? d t 1
,
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ing that the ADC is no longer in an overloaded condition.
a .
7,015,853 B1
3/2006 Wolff et al.
7,049,990 B2
5/2006 Ranganathan
25 Claims, 17 Drawing Sheets
10
62
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US 7,474,247 B1
Page 2
US. PATENT DOCUMENTS
7,245,246 B2
7,345,607 B1*
2005/0162222 A1
2007/0032734 A1
2007/0208262 A1*
7/2007 Ihs et al.
3/2008 Frigaard et al. ........... ..
7/2005 HeZar et al.
2/2007 Naja? et al.
9/2007 Kovacs ..................... ..
OTHER PUBLICATIONS
341/143
U.S. Appl. No. 11/861,920, ?led Sep. 26, 2007 entitled “Implantable
Medical Device With Low Power Delta-Sigma Analog-to-Digital
Converter” reference N0. P0028368.00.
600/509
* cited by examiner
US. Patent
FIG. 1
Jan. 6, 2009
Sheet 1 0f 17
US 7,474,247 B1
US. Patent
Jan. 6, 2009
Sheet 3 0f 17
US 7,474,247 B1
107
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IMPLANTABLE MEDICAL DEVICE
REFERNECE
AND BIAS
GENERATOR
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MODULE
CLOCK
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FIG. 3
TELEMETRY
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US. Patent
Jan. 6, 2009
Sheet 4 0f 17
US 7,474,247 B1
US. Patent
Jan. 6, 2009
Sheet 5 0f 17
US 7,474,247 B1
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Sheet 14 0f 17
GENERATE A CLAMP SIGNAL WHEN AN INTEGRATOR OF
THE ADC IS OPERATING IN A CLAMPED MODE
US 7,474,247 B1
’_\/ 180
l
REGISTER A CLAMP EVENT FOR A TIME INTERVAL IF
THE CLAMP SIGNAL IS PRESENT FOR AT LEAST
’\/ 182
A PORTION OF THE TIME INTERVAL
l
COUNT A NUMBER OF TIME INTERvAI_S FOR
WHICH A CLAMP EvENT wAS REGISTERED IN
A SET OF coNTIGuouS TIME INTERvAI_S
/\/ 184
l
DETERMINE THAT THE ADC IS IN AN OVERLOAD
CONDITION BASED ON A COMPARISON OF THE
NUMBER OF TIME INTERVALS TO A THRESHOLD
FIG. 14
N 186
US. Patent
Jan. 6, 2009
Sheet 15 0f 17
US 7,474,247 B1
GENERATE A LOW TOGGLE SIGNAL IF A QUANTIZER OF THE
ADC OUTPUTS THE SAME VALUE DURING A THRESHOLD /'\/ 190
NUMBER OF CONSECUTIVE CLOCK CYCLES
l
REGISTER A LOW TOGGLE EVENT FOR A TIME INTERVAL IF
THE LOW TOGGLE SIGNAL IS PRESENT FOR AT LEAST A "\/ 192
PORTION OF THE TIME INTERVAL
l
COUNT A NUMBER OF TIME INTERVALS FOR WHICH A LOW
TOGGLE EVENT wAs REGISTERED IN A sET OF
CONTIGUOUS T|ME INTERVALS
’\/ 194
l
DETERMINE THAT THE ADC IS IN AN OVERLOAD CONDITION
BASED ON A COMPARISON OF THE NUMBER OF TIME
/\/ 196
INTERVALS To A THRESHOLD
FIG. 15
US. Patent
Jan. 6, 2009
Sheet 16 0f 17
GENERATE A CLAMP SIGNAL WHEN AN INTEGRATOR OF
US 7,474,247 B1
,_\/ 200
THE ADC IS OPERATING IN A CLAMPED MODE
I
REGISTER A CLAMP EVENT FOR A TIME INTERVAL IF THE
CLAMP SIGNAL IS PRESENT FOR AT LEAST A PORTION OF
N 202
THE TIME INTERVAL
I
COUNT A FIRST NUMBER OF TIME INTERVALS FOR WHICH A
CLAMP EVENT WAS REGISTERED IN A SET OF CONTIGUOUS "\/ 204
TIME INTERVALS
I
GENERATE A LOW TOGGLE SIGNAL IF A QUANTIZER OF THE
ADC OUTPUTS THE SAME VALUE DURING A THRESHOLD N 206
NUMBER OF CONSECUTIVE CLOCK CYCLES
I
REGISTER A LOW TOGGLE EVENT FOR A TIME INTERVAL IF
THE LOW TOGGLE SIGNAL IS PRESENT FOR AT LEAST A "\/ 208
PORTION OF THE TIME INTERVAL
I
COUNT A SECOND NUMBER OF TIME INTERVALS FOR
WHICH A LOW TOGGLE EVENT WAS REGISTERED IN A SET ’\/ 210
OF CONTIGUOUS TIME INTERVALS
I
DETERMINE THAT THE ADC IS IN AN OVERLOAD CONDITION
BASED ON A COMPARISON OF THE FIRST NUMBER OF TIME "\/ 212
INTERVALS TO A FIRST THRESHOLD
I
DETERMINE THAT THE ADC IS IN AN OVERLOAD CONDITION
BASED ON A COMPARISON OF THE SECOND NUMBER OF
TIME INTERVALS TO A SECOND THRESHOLD
FIG. 16
"\/ 214
US. Patent
Jan. 6, 2009
Sheet 17 0f 17
US 7,474,247 B1
DETERMINE THAT AN ADC IS APPROACHING AN OVERLOAD
CONDITION BASED ON AT LEAST ONE SIGNAL FROM THE "\/ 34o
ADC
I
GENERATE A WARNING SIGNAL IN RESPONSE To THE
DETERMINATION
342
N
I
SWITCH FROM A NORMAL SLEW OPERATING MODE TO A
HIGH SLEW OPERATING MODE IN RESPONSE To THE
WARNING SIGNAL
f\, 344
I
DETERMINE THAT THE ADC IS No LONGER APPROACHING
AN OVERLOAD CONDITION
346
N
I
DEACTIVATE THE WARNING SIGNAL IN RESPONSE T0 THE
DETERMINATION
348
’\/
I
SWITCH FROM A HIGH SLEW OPERATING MODE TO A
NORMAL SLEW OPERATING MODE IN RESPONSE TO
DEACTIVATION OF THE WARNING SIGNAL
FIG. 17
/_\/ 35o
US 7,474,247 B1
1
2
DETECTING OVERLOADING OF AN
ANALOG-TO-DIGITAL CONVERTER OF AN
IMPLANTABLE MEDICAL DEVICE
SUMMARY
In general, this disclosure is related to detecting overload
Within an analog-to-digital converter (ADC) of an implant
able medical device (IMD). The IMD may be exposed to
TECHNICAL FIELD
non-physiological signals, such as electro-magnetic interfer
This disclosure relates to implantable medical devices and,
more particularly, analog-to-digital conversion in implant
able medical devices.
ence (EMI), Which can induce large voltages on one or more
of electrodes. In the presence of these large voltages, and
ADC of IMD may become overloaded, thereby causing the
ADC to output data that includes errors. The IMD may ana
BACKGROUND
lyZe the incorrect data, and erroneously interpret the data as
indicating a condition that does not exist, or fail to indicate a
condition that does exist. This may cause the IMD to incor
In a variety of applications, implantable medical devices
are used for one or both of monitoring or delivering therapy to
rectly apply or disable therapy.
a patient. For example, cardiac pacemakers typically monitor
electrical signals from the heart, i.e., an electrocardiogram
To avoid these situations, an IMD according to the inven
tion may include an overload detection module that deter
mines Whether the ADC is operating in an overload condition
(ECG), and deliver electrical stimulation to the heart, via
electrodes. The electrodes may be positioned Within the heart,
and coupled to the pacemaker by intravenous leads, or may be
positioned subcutaneously using any non-intravenous loca
20
due to large voltages. When the overload detection module
determines the ADC is operating in the overload condition for
a particular period of time, the overload detection module
tion, such as beloW the muscle layer or Within the thoracic
may send an overload signal to a processor that receives the
cavity, for example.
output of the ADC. The overload signal noti?es the processor
that the ADC is operating in or is close to operating in the
overload condition. In response to the indication from the
ADC, the processor of the IMD may disregard the output of
the ADC. The processor may continue to disregard the output
In the case of demand pacing, for example, a cardiac pace
maker monitors the ECG to determine Whether an intrinsic
cardiac depolarization, e.g., a P-Wave or R Wave, occurs
Within a rate interval. If an intrinsic depolariZation occurs, the
pacemaker resets a timer and continues to monitor the elec
25
of the ADC until the overload signal is deactivated, thereby
trical signals from the heart. If an intrinsic depolarization
does not occur, the pacemaker delivers one or more electrical
pulses to the heart, and resets the timer.
As another example, an implantable medical device may
monitor electrical signals Within the brain, e.g., an electroen
30
cephalogram (EEG), sensed via electrodes. An implantable
medical device may monitor the EEG to, for example, iden
tify epileptic seiZures, or other neurological issues. In some
35
cases an implantable medical device may deliver electrical
stimulation to the brain, or other tissue Within the patient, in
response to or based on the analysis of the EEG. In other
examples, implantable medical devices may monitor any of a
variety of signals generated by any of a variety of sensors
40
indicating that the ADC is no longer in an overloaded condi
tion.
Alternatively, or additionally, the IMD may include an
overload prediction module that detects When the ADC is
approaching an overload condition. In response to the detec
tion, the ADC may either output a Warning signal to the
processor and/or adjust the operation of the ADC in response
to the prediction. The ADC may, for example, be repro
grammed from a normal counting mode that counts by +/—l to
a high sleW count mode that counts by +/—2. Alternatively, or
additionally, the ADC may be clocked at an increased clock
rate to operate in a high sleW mode. In this manner, the ADC
may accommodate for the detected conditions to better track
based on physiological parameters of a patient, such as pres
the inputs.
sure, impedance, temperature, or physical motion.
Historically, implantable medical devices have used ana
process the ECG, e.g., to detect P-Waves and R-Waves. More
In one embodiment, a method comprises converting an
analog input signal from a sensor into a digital signal With an
analog-to-digital converter (ADC) of an implantable medical
device, determining that the ADC is in an overload condition
based on at least one signal from the ADC and disregarding
recently, use of digital signal processing for this purpose has
the digital signal by a processor of the implantable medical
been considered or implemented.
device in response to the determination.
log circuitry to process or analyZe such physiological signals.
For example, many pacemakers have used analog circuitry to
45
Digital signal processing requires conversion of the analog
signal, e.g., ECG, to a digital signal using an analog-to-digital
50
converter (ADC). One type of ADC is a delta-sigma ADC. A
an analog input signal from a sensor into a digital signal, an
overload detection module that determines that the ADC is in
delta-sigma ADC tracks the changes in the analog input sig
nal by comparing the input signal to a feedback signal.
In general, based on its complexity and sampling rate, there
is a limit to the magnitude and rate of change of an input signal
an overload condition based on at least one signal from the
ADC and a processor that disregards the digital signal in
55
that a delta-sigma ADC can track. Implantable medical
devices can be exposed to electro-magnetic interference
(EMI) that can induce large voltages on the leads or sensor
inputs. In the presence of EMI, a delta-sigma ADC can be
overloaded so that incorrect data streams are generated,
In another embodiment, an implantable medical device
comprises an analog-to-digital converter (ADC) that converts
response to the determination.
In another embodiment, an implantable medical device
comprises an analog-to-digital converter (ADC) that converts
an analog input signal from a sensor into a digital signal,
Wherein the ADC includes a clamping integrator that gener
60
Which may be incorrectly interpreted by a system that ana
ates a clamp signal When the clamping integrator is operating
in a clamped mode, an overload detection module that deter
mines that the ADC is in an overload condition based on the
lyZes the output digital signal. For example, a cardiac pace
maker may incorrectly interpret loW frequency shifts in the
output digital signal caused by EMI to be intrinsic cardiac
mode may incorrectly inhibit delivery of pacing pulses in the
clamp signal from the ADC, and a processor that disregards
the digital signal in response to the determination.
In another embodiment, an implantable medical device
comprises an analog-to-digital converter (ADC) that converts
presence of EMI.
an analog input signal from a sensor into a digital signal, an
activity. In this case, a pacemaker operating in a demand
65