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A Very Low Power CMOSMixed-Signal IC for Implantable
Pacemaker Applications
Louis S. Y. Wong
Raymond Okamoto
Joseph Ahn
St. Jude Medical
Cardiac Rhythm Management Division
Sunnyvale, CA
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Questions:
(1) What year was the 1st
pacemakerintroduced?
(2) How many transistors are there in the1st pacemaker?
(3) How many transistors are there intodays (2004) pacemaker?
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Outline
Overview of Cardiac Pacemaker Overview Sensing
Overview Output Therapy System
Overview Battery Management System Overview Low Power Logic Design
Overview Low Power Memory Design
Overview (MEMS) Activity Sensor Overview (MEMS) Magnet Sensor
Silicon Results
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Overview of Cardiac Pacemaker
What is it?
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Cardiac Pacemaker System
Picture of an actualImplantable Pacemaker
2 inch
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Pacemaker Simplified Block
Diagram
ElectrodeConfig.Switches
A/DConverters
&Detectors
ProgrammableLogic
&Timing Control
&TherapyAlgorithms
Memory
TelemetryCircuit
PhysiologicSensor
Battery PowerManagementSystem Voltage
&Current
ReferenceGenerators
Monitoring&
MeasuringSystem &
ADC
High VoltageMultiplier
High
VoltageOutputPulse
Generator
Sensing&
FilteringAmplifiers
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Die Photograph
7000m
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Overview of Cardiac Pacemaker
Cardiac Sensing System
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Sensing System Block Diagram
Passive Filter
Network
Out # 1
Out # N
MUX
MUXPassive Filter
Network
Passive FilterNetwork
M
UX
MUXPassive Filter
Network
ADC
ADC
CardiacInputs
(V-mV)
Low-Power Switched-Capacitor
Filters/Amplifiers
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Low Power SC Circuits - Problem
Chold
Vin
I1
I3
I2
VoutVhold+
-
Vdd
Vss
A Sample-hold Amplifier
used to illustrate the problem
Illustrated by a SC SH amplifier:
Residual leakage current (~pA)when CMOS switch is off
Cardiac/Neuro-signals have lowfrequency content ~0.1Hz
Signal amplitude of interest ~V-mV
If leakage=1pA, Chold=1pF, hold time=100mS, then
Vout drift = 100mV (Unacceptable)
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Leakage Cancellation Technique -
Concept
Chold
Vin
I1
I3
I2
VoutVhold
Icancel=I1+I2+I3
Self-adjusted currentsource
+
-
Vdd
Vss
The concept of
Leakage Cancellation Technique
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Leakage Cancellation Technique -
Concept
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.00 0.20 0.40 0.60 0.80 1.00
Time (sec)
Voltage(V)
Vrep
Vhold
Chold
Vin
I1
I3
I2
Vhold
Crep
I1
I3
I2
Vrep
Vdd
Vss
Vdd
Vss
Mp
Mn
Mp
Mn
Introducing the Replica SH Circuit, with Crep
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Leakage Cancellation Technique - Design
A design example of the Leakage Cancellation Technique
CrepChold
VA
Aoutf
CrepChold
I
dt
dV offsetdeltahold
+=
=
)(
Chold
Vin
I1
I3
I2
Vout
Vhold
Crep
I1
I3
I2
Vdd
Vrep
A1
Vss
M1
Replica SH Circuit
Vdd
Vss
M5
Leakage current
cancallation
feedback
-
+
+
-
M4
M7M3
M6M2
M8
Vdd
Vss
Vdd
Vss
Mp
Mn
Mp
Mn
Aout
I cancel
I cancel
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Leakage Cancellation Technique -
Results
SHA (Original)
1Hz sine input, Fs=10Hz
I leakage ~ 0.1pA total
SHA with Leakage Cancellation
1Hz sine input, Fs=10Hz
I leakage < 0.01pA (effective)
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Overview of Cardiac Pacemaker
ADC
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8-bit ADC
ADC is used to digitized the cardiac sensingoutputs
Successive Approximation Architecture
Typical power consumed by:
S/H
DAC
Comparator
To minimize power, this ADC:1. Uses capacitor-array for both DAC and SHA
2. Use an integrated-opamp for both SHA and
comparator
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8-bit ADC Architecture
Successive ApproximationControls and Registers
C 128C2C 4C
Vin VREF_1VREF_0
SHA & Comparator
Clk_16K
8b Output
Done
CompOut
Integrated S/H-comparator
SHA Out
C 2C 4C 8C C 2C 4C 8C
Capacitor array for S/H and DAC
Cs
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8-bit ADC Timing
Clock
Output[7:0]
Analog Inpu
Data1
Sample1
SHA
SA
Done
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8-bit ADC Measured Results8-bit ADC INL
-2
-1
0
1
2
1 52 103 154 205 256
Code
INL(LSB)
10Hz input sinewave (-6dB of full scale)
-100
-80
-60
-40
-20
0
0 100 200 300 400 500
Frequency (Hz)
Amplitude(dB)
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8-bit ADC Measured Results
~ 150nA @ 2VSupply Current (On)
~ 20nASupply Current (Standby)
500mVppInput Voltage Range
< 1.5 LSBDNL
< 3 LSBDC offset error
< 10% FSGain error
> 48 dBSFDR
< 1.5 LSBINL
1 KS/sSampling Rate
8-bitsResolutionValueParameter
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Complete Sensing System
Measurement Setup
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Complete Sensing System (SC Filters
and ADC) Example ECG Results
An example ADC output of Electrocardiogram (ECG) processed by different SC filters.
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Overview of Cardiac Pacemaker
Output Therapy System
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High Voltage Output System
To stimulate the heart muscle (e.g. initiate aheart beat), a high-voltage output pulse isdelivered to the heart through the pacing leads.
Multiplying the battery voltage is needed togenerate the necessary high voltage.
A Voltage Multiplier Circuit is used
The amplitude and pulse width of the high-
voltage output pulse is customized for thepatients.
A High Voltage DAC is used
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High Voltage Multiplier
(Not to scale)
Vreg
2*Vdd
3*VddVoltage on chip
Hi-volt outputpulse
On-chipanalog &
digital
Batterymanagement& references
Usage
VoltageMultiplier
Voltageregulator
Battery(Vdd ~ 2.8V)
Voltage Multipliers and Regulators for the complete IC
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Capacitive Voltage Multiplier
Design
1
2
C2
1
2
2
2
1
1
C1
Cres2 =2*Vdd
Cres3 =3*Vdd
Vdd
Vss
Capacitive 2X and 3X voltage multiplier
1, 2: Non-overlapping clocks
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High-Voltage DAC Design
Hi-Voltage OutputPulse Generator:
Switched-Cap DAC
pre
out
pre
out
C2
outC1
pre
Vref
Vss
OutputPulse
Vout
Hi-Voltage OutputPulse Generator:Equivalent model Hi-Volt
DAC
out
Power Supply = 2* or 3* Vdd
PulseAmplitude
Hi-Volt OutputPulse
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High-Voltage DAC Design
Vref
Vss
2-in-1 (HV/LV)CMOS opamp
Vout
VbVb
Vdd
V+ V-
Supply = 2*Vdd or 3*Vdd
Freq
CompVpre
Vss
NormalMOSFET
Hi-VoltMOSFET
pre
out
C2 outC1
pre
VoutVpre
2-in-1 opamp
pre
High-Voltage DAC utilizing2-in-1 opamp
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High-Voltage DAC Measured
ResultsOutput Pulse Vs input code
0
1
2
3
4
5
6
7
8
9
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
Digital input code
OutputPulse(V)
Linearity of Output Pulse Amplitude
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Overview of Cardiac Pacemaker
Battery Management System
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Battery Management System
A primary battery (~2.8V) is typically used for a5-10 years of device life time.
Battery status must be accurately monitored to
guarantee reliable operations. The status of the battery is determined bymeasuring its output voltage. However, it mayNOT be very accurate due to the flat output
voltage characteristics. To enhance accuracy:
A Battery Charge monitoring circuit(Battery Charge Meter) is proposed.
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Battery Management System
Block Diagram
PrimaryBattery
Voltage ReferenceGenerators
VTrip1
VTrip2
VTrip3
Battery Volt Detectors
+
-
Status_1
Status_2
Status_3
To the restof the chip
Battery Management System
Battery Charge Meter
VCO
BinaryCounter
32-bitChargeMeter
RI(t)
Vin_p Vin_n
Battery Charge Meter:
Low offset, high linearity VCO
Continuously monitors 0.5A-100A of current Very low power consumption
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Battery Management System
Battery Charge Meter
VCO output frequency:
The output of the counter:
Re-arrange to give:
Knowing Count, KVCO and R, the total chargedepleted from the battery can be accurately
calculated.
RtIKFreq VCOVCO = )(
dtRtIKdtFreqCount VCOVCO == )(
RKCountdttIeChQVCO
=== )(arg
C
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Battery Charge Meter - Design
Voltage Referencegenerators
VTrip1
VTrip2
VTrip3
Battery volt Detectors
+-
Status_1
Status_2
Status_3
To the restof the chip
PrimaryBattery
Battery Management System
Battery charge meter
VCO
Binary Counter 32-bitChargeMeter
RI(t)
ComparatorVCO
output
Integrator(switched-
cap)
Vin_pVin_n
Vref_p
Vref_n
Vref_p
Vref_n
Vramp
IntegratorVramp
Vdd
Vss
VCOOut
Time
K
Battery charge meter VCO block diagram
Vin_p Vin_n
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Battery Charge Meter VCO Design
int
__ )()_(
C
CVVstepperV
sninpin
ramp
=
2
ComparatorLow-Power Auto-Zero
Switched-Cap Integrator
Vref_p
Vref_n
VrampK
K
K
K
K
K
11
K
CintCS
K
Vin_pVin_n
2
1
2
1
VCOOutputs
1,2: Non-overlapping clocks
Comparator VCOoutput
Integrator
(switched-cap)
Vin_pVin_n
Vref_p
Vref_n
Vref_p
Vref_n
Vramp
IntegratorVramp
Vdd
Vss
VCO
OutTime
K
Battery charge meter VCO block diagram int__
__
)(2
)(
CVV
CFVVFreq
nrefpref
ssninpin
VCO
=
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Battery Charge Meter Measured
Results
~ 100nA
@ 2.8V
Supply Current (On)
< 10nASupply Current
(Standby)
< 150VInput Offset Error
8 KHzSampling Rate
80 Hz/VVCO Gain
0mV - 50mVInput Range
ValueParameterBattery Charge Meter - VCO Linearity
0
20
40
60
80
100
120
0 0.005 0.01 0.015 0.02 0.025
Differential Input Voltage (V)
OutputFrequency(Counts
per60sec)
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Battery Charge Meter Measured
ResultsBattery Charge Meter - VCO Linearity
0
20
40
60
80
100
120
0 0.005 0.01 0.015 0.02 0.025
Differential Input Voltage (V)
Output
Frequency(Countsper60sec)
To the restof the chip
Battery charge meter
VCO
Binary CounterCounterOutput
R
Vin_p Vin_n
Now, we have:
Kvco = 80Hz/V, R = 500 and assume a 1A-h battery
At the end of battery life, the counter output will reach:
144,000,000 counts
(It is also independent of the battery output voltage!)
32-bitBinary
Counter
RK
CountdttIeChQ
VCO === )(arg
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Overview of Cardiac Pacemaker
Low Power Logic Designby:
Raymond OkamotoRaymond Okamoto received his B.S. ECE from U.C. Santa
Barbara. He has 15+ years in both hardware and
software designs. He has previous worked for
ArgoSystems, Trimble Navigation, Intel and Mentor
Graphics. He has designed both GPS and networkingASICs as well as other hardware systems. He joined
St Jude Medical in 2003.
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Programmable Logic, Timing Control and
Therapy Algorithms
CPU Configuration Registers
Timing and control for Analog Functions
Finite State Machine under CPU control for TherapyAlgorithms
Hardware Control Finite State Machine in backup (fail
safe) mode to delivery therapy
RTL to GDSII design flow Low Power Design (nW)
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Digital Core Lower Power Techniques
Minimize Voltage
Trade off custom low power library vs standard library
Backend Flow with multiple power
Minimize Clock Frequency
Gated Clock Design
Review of minimum clock frequency required
Minimize Capacitance (Logic Area)
Design for minimum logic at the RTL level
Reduce clock domains (trade off with min clock frequency)
Customize Clock Synthesis Tool for low power vs high speed trees
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Clock Tree Synthesis
Custom Approach to minimize buffer insertion
5 : 1 Aspect Ratio for Digital Core
Hand Placed
Initial Clock Buffer
Minimize Buffer Insertion to
balance system clock to 8
Clock Domains
Added hand placed buffers
Around clock divider Flip Flops to minimizeClk to Q Delay
( reduce buffers for clock balancing)
Clock Divider
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Overview of Cardiac Pacemaker
Low Power Memory Designby:
Joseph AhnJoe Ahn received his B.S. and M.S. EE from Lehigh
University. He has 11+ years in hardware design. He
has previous worked for Virtual Silicon Technology, C-
Cube Microsysytems and Aspec Technology. He has
designed various components including SRAMs,ROMs, datapath blocks, I/Os and standard cells. He
joined St Jude Medical in 2002.
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Ultra-Low Power SRAM for
Pacemakers and ICDs
The three components of power
Capacitance
Reduce switching of high capacitive nodes
Voltage
Reduce the voltage swing
Frequency Lower operating frequency
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Reduce switching of high
capacitive nodes
Smaller subsections
Shorter word-lines
and bit-lines
Disable inactivecircuitry
Local decoders vs.
global decoders
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Reduce the voltage swing
Partial voltage swings
Low power sense amp
Special manufacturing
processes Lower operating voltage
Leakage current
High Vt devices
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Lower operating frequency
Lower operating frequency
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Overview of Cardiac Pacemaker
MEMS Activity Sensor
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Patient Activity Sensor
Patient activity sensor is used to:
Sense patients body movements, and to
determine the appropriate pacing rates for
correct therapy. An Accelerometer Sensor is placed inside
the device.
Be able to differentiate between patientmovements from surrounding noise (eg
vehicle vibration, vacuum cleaner)
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Activity Sensor Interface Circuit
Piezo-electricSensor
It generates a charge/voltage proportional to the patients
acceleration. The VCO generates an output signal whose frequency is
proportional to the voltage sensed at the input. The numberof cycles of the VCO output is proportional to the averagepatient physical accelerations.
Low power consumption ~ 40nA
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Overview of Cardiac Pacemaker
MEMS Magnet Sensor
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Magnet Detection Sensor
A magnet detector can be used to:
Open the telemetry channel
Disable the device Put the device into a special operating
mode, e.g. in emergency
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Magnet Detection Sensor
Two types of magnetic sensors are
typically used:
1. Reed Switch2. Giant Magneto Resistive (GMR)
Sensor
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Reed Switch Interface Circuit
Low pass filter
Debouncing circuit to filter out glitches
Very low power consumption ~ 20nA
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Overview of Cardiac Pacemaker
Silicon Results
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Silicon Results
7mm x 7mmDie Size
~ 8WPower Consumption
2.0V 2.8VSupply Voltage
ValueParameter
Recommended