ultra low power analog integrated circuits for implantable...
TRANSCRIPT
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 1
Ultra Low Power Analog Integrated Circuits
for Implantable Medical Devices
Fernando Silveira
Universidad de la República, Uruguay
CCC Medical Devices
nanoWattICs
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 2 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 2
Objectives of this talk
• Introduce the needs and characteristics of Active Implantable Medical Devices (AIMDs) from the circuit designer point of view.
• Present the techniques and circuits applied in Analog ULP
• Device Modeling
• Design Methodology
• Circuit techniques
• Show the current research and development topics and prospects of the area
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 3 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 3
Engineering School Universidad de la Republica
• Founded 1888, approx. 1k new students / year, 670 teaching staff
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 4 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 4
• Since 1991
• Under Graduate & Graduate Teaching (MSc, PhD)
• Research
• Design of Analog / RF and Mixed-Signal Integrated Circuits, particularly Ultra-Low Power (ULP)
• Also works on ULP Digital / DC-DC and Embedded
• Strong links with Research groups abroad
• Industrial Experience
• Implantable Medical Devices
• 2007: spin-off: NanoWattICs
Microelectronics Group
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 5 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 5
Implantable Devices in Uruguay
Feb. 3, 1960: Drs. O. Fiandra and R. Rubio
performed the first effective pacemaker implant to a human being in the world.
1969: Dr. O. Fiandra founded CCC to develop and manufacture pacemakers
1999: CCC develops a pacemaker line based on an DDDR ASIC designed by the Microelectronics Group of Universidad de la Republica
Today: CCC designs and manufactures active implantable devices and complete medical systems for third parties.
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 6 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 6
Outline
I. System: Active Implantable Medical Devices Today
II. Transistors and Circuits: Analog Design for ULP.
Transistor Modeling.
Design Methodology.
III. Circuit Techniques: Implementation of AIMDs blocks
IV. Conclusions and Prospects
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 7 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 7
Active Implantable Medical Devices (AIMD)
Implantable: Introduced inside the body by a medical procedure and intended to remain there after the procedure.
Active: Including a Power Source
Not considered here:
Passive implants (e.g. bone prostheses, valves, stents)
Wearable / Portable / Swallowable (!) Active Medical Devices
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 8 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 8
Cardiac Pacemaker: first implantable device, 1960
AIMDs: Main Historical Milestones (I)
Cochlear Implants (1960s -)
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 9 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 9
Cardiac Defibrillators (1980)
AIMDs: Main Historical Milestones (II)
Deep Brain Stimulator for
Parkinson (1995)
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 10 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 10
• Heart Failure
• Obesity
• Diabetes
• Neurostimulators:
• Pain control
• Blood pressure control
• Foot drop correction
• Urinary incontinence
• Sleep Apnea
• …
• Patient monitoring
• Brain – computer interface
AIMDs: Some of the new developments
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 11 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 11
• Pacemaker:
• Goal: Treat Bradycardia (slow heart rythm) and conduction disorders between atria and ventricles
• How: Stimulating to contract the heart when it does not contract spontaneously (“watchdog”)
• Sensing of:
• cardiac muscle signals that indicate ventricles / atria contraction
• other indicators of physical activity, additionally in some cases
Some system examples
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 12 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 12
• Stimulation (Open Loop)
• Early Pacemakers
• Cochlear Implants
• Deep Brain Stimulators for Parkinson
• Neurostimulators (sometimes “Man/Woman in the loop”)
• Stimulation and Sensing (Closed Loop)
• Cardiac area (Pacemakers, Defibrillators, Heart Failure)
• Obesity
• Some Neurostimulators
• Only Sensing
• Implanted “long term Holter” (“insertable loop recorder”)
• Sensing + external actuation: Brain-computer interface
Basic Functions
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 13 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 13
Stimulation: Voltage mode
• E.g.: Pacemakers
• 0.1V … 7.5V
• 50ms … 1.5ms
• Requires battery voltage multiplier.
• RL: 500 Ohms typ.
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 14 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 14
• Neurostimulators and others
• 0.1mA … 10mA
• 30ms … 300ms
• Load voltages up to 15V => Requires battery voltage multiplier
Stimulation: Current mode
t
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 15 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 15
Sensing: Medical signals in general
• Low frequency: from < 1 Hz to a few kHz (neural signals)
• Low amplitude: mV to mV
• Variability:
" Most measured quantities vary with time, even when all controllable factors are fixed. Many medical measurements vary widely among normal patients, even when conditions are similar “ (Source:J. Webster, Medical Instrumentation. Application and Design).
Objective of most analog signal processing: qualitative detection for closed loop control.
Traditionally advantage to analog implementation in terms of consumption, process scaling is changing this
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 16 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 16
• Biopotentials:
• mioelectric signals (mVs, 100s Hz - 1kHz)
• cardiac signals (mVs, 10s Hz – 300Hz)
• neural signals (mVs, up to 8kHz)
• Impedance (tens of mOhms => mVs, few Hz)
• Movement (Physical activity, position) => accelerometer (mVs (sensor dependent), up to 10Hz)
Sensing
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 17 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 17
• Telemetry
• Inductive (up to 10cms)
• 403 MHz MedRadio Band (a couple of meters)
• Battery Supervision (Voltage / Impedance / Consumed Charge Measurement)
• Lead Impedance Measurement
• Magnet Sensor (Reed Relay / Hall Sensor)
• Battery Recharge (if applicable)
• Control: Microcontroller & Firmware
Auxiliary Functions
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 18 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 18
Non-implantable System Components
Medical System Components
IPG Leads
Programmer
System
PSA
Patient
wand
Battery
charger
Logger
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 19
Example: Implantable Pacemakers
Stimulus
Sense Channel
Micro controller
Battery Supervision
Activity Sensing Lead
Selection (polarity)
Telemetry
Amplification, Filtering and Detection
Programmable Voltage Multiplier
0.1VDD a 2-3 VDD
35% / 6mA
30% / 5mA
18% / 3mA
17% / 2.8mA
Approx. Consumption Distribution
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 20
Example: Closed Loop Stimulator for Drop Foot Correction (I)
• Neurostep System (Simon Fraser Univ, Canada, Neurostream Technologies)
• Closed loop operation based on neural signal sensing and neural stimulation
• On clinical trials
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 21
Example: Closed Loop Stimulator for Drop Foot Correction (II)
http://www.youtube.com/watch?v=xH2vNu2BbnU
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 22 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 22
General Requirements: Size
Currently approximately 12 cc (5cm x 4cm x 0.6cm)
Approx. 30 to 40% occupied by the battery
Less consumption = Smaller size @ Equal Service Life
Biotronik
1968- 1998 (Source: M. Wilkinson, course: MST for Medical Devices)
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 23 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 23
• Lithium-Iodine Battery (Li/I2)
• THE pacemaker battery during almost 30 years
• Beguining of life: 2.8V, Operation down to 2.0V.
• High internal impedance, specially near depletion (several kohms)
• Must be taken into account in complete device (power decoupling) and circuit design (instantaneous consumption, PSRR)
• Common problem with other non-implantable batteries (e.g LiMn02)
• Capacity: In the order of 1 Ah = 114 mA . Year
General Requirements: Batteries (I)
0
0.5
1
1.5
2
2.5
3
0 20 40 60 80 100
Percentage of Nominal Capacity Delivered (%)
Voltage(V
dc)
0
2000
4000
6000
8000
10000
12000
14000
16000
Inte
rnal Im
pedance (
Ohm
s)
Voltage
Internal Impedance
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 24 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 24
• For higher instantaneous consumption devices, lower impedance required
• Lithium-Silver-Vanadium-Oxide (Li/SVO)
• Lithium-Carbon-Monofluoride (Li/CFx)
• QMR / QHR: Li + combined SVO / CFx
• Being applied also in pacemakers recently.
• For higher average consumption devices:
Rechargeable lithium batteries (since approx. year 2000, capacity in the order of 0.3Ah)
Direct powering from RF energy transmitted transcutaneously
General Requirements: Batteries (II)
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 25 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 25
General Requirements: Battery and Consumption
• Capacity: In the order of 1 Ah = 114 mA . Year
• Consumption
Service Life: 6 to 12 years => consumption: 19 mA to 9 mA
Average consumption due to stimulation (pacemakers): 3 mA to 12 mA=> Unavoidable
State of the art: average consumption internal to the circuit around 5 to 10mA
Consumption internal to the circuit: 50% to 75% of total consumption
There is room and need for improvement
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 26 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 26
General Requirements: Safety and Reliability
This is not acceptable !!!
Source: Quino
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 27 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 27
General Requirements: Safety and Reliability
Reliability => Frequency and probability of faults
Safety: Involves many aspects, particularly:
=> A single fault must not provoke a catastrophic event
High Reliability => Probability of single fault is low and double fault is virtually impossible
+ Safety
=> Probability of malfunctioning is low
=> Catastrophic Failure: virtually impossible
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 28 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 28
General Requirements: Safety and Reliability
Involves all the stages:
System and Circuit Design
System and Circuit Verification, Qualification and Medical Validation
Medical Device Application, Configuration and Use
Strongly conditions design: E.g. Limiting DC leakage towards the heart under single fault conditions => external capacitors
Importance of paying attention from the very beginning to applicable standards on AIMD safety, risk analysis and applicable regulations.
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 29 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 29
Outline
I. System: Active Implantable Medical Devices Today
II. Transistors and Circuits: Analog Design for ULP.
Transistor Modeling.
Design Methodology.
III. Circuit Techniques: Implementation of AIMDs blocks
IV. Conclusions and Prospects
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 30
• Bipolar (BJT) Analog Design:
gm = Ic/UT
– Basically 1 degree of freedom: Ic
• MOS Analog Design:
gm = f(ID, W, L)
– 3 degrees of freedom
– Traditionally: only part of the design space: the strong inversion (above threshold) region
Introduction
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 31
-0.5 0 0.5 1 1.5 2 2.510
-14
10-12
10-10
10-8
10-6
10-4
10-2
VG(V)
ID(A
)
Subthreshold
Current
Leakage Current
VT0
-1 0 1 2 30
2
4
6
ID(m
A)
VG(V)
VT0
MOST Inversion Regimes (1)
Strong Inversion (S.I.)
ID(VG-VT)2
Weak inversion:
IDeVG/(n.UT)
Moderate inversion
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 32
0 0.5 1 1.5 2 2.5
10-10
10-5
VG(V)
ID(A
)
Diffusion Current
Drift Current
VT0
MOST Inversion Regimes (2)
Strong Inversion (S.I.)
ID(VG-VT)2
Weak Inversion (W.I.)
IDeVG/(n.UT)
UT=k.T/q
n: slope factor
Moderate Inversion (M.I.)
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 33
All regions, continuous MOST models
• EKV (Enz, Krummenacher, Vittoz, EPFL, AICSP 1995): originally mathematic interpolation between strong and weak inversion equations, now physical
• ACM (Advanced Compact Model, A. Cunha, C. Galup-Montoro, M. Schneider, UFSC, IEEE JSSC 1998): Physical model.
• … or experimental / simulation curves
0 0.5 1 1.5 210
-15
10-10
10-5
VG(V)
ID(A
) Strong Inversion
Approximate Limit
Weak Inversion
Approximate Limit
VT0
Weak Inversion
ModelStrong Inversion
Model
General Model
Leakage
Current
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 34
“Intrinsic” MOS Amplifier
A0=gm/gd A (dB)
f(Hz)
fT=gm/(2..CL)
V
vi
vo
CL
ID
DDV
vi
vo
CL
ID
DD
vi
vo
CL
ID
DD
D
d
D
mA
D
m
d
mom
I
g
I
gV
I
g
g
grgA ..0
T
0
0
L
mT
f2
s.A1
AA ,
C2
gf
• Consumption: ID
• Speed gm/CL
• CL: total: external + parasitics
• Speed - Consumption trade-off : gm/ID
OTA: Operational Transconductance Amplifier
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 35
gm/ID vs. VG
G
DGD
DD
m
V
)Ilog(VI
I
1
I
g
• gm/ID is the slope of ID vs. VG in log scale
Maximum in WI
Equal to 1/(n.UT)
n typ: 1.3 a 1.5 -0.5 0 0.5 1 1.5 2 2.5
10-14
10-12
10-10
10-8
10-6
10-4
10-2
VG(V)
ID(A
)
Subthreshold
Current
Leakage Current
VT0
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 36
gm/ID vs. ID
10-15
10-10
10-5
100
0
5
10
15
20
25
30
35
40
ID(A)
gm
/ID
(1/V
)
gm/Ic, transistor bipolar
• As the current increases, the “gm generation efficiency decreases”
• To reach the maximum frequency allowed by the technology:
=> high gm => high current => strong inversion => low efficiency
W/L =100 and 0.8mm technology.
Bipolar Transistor:
gm/IC
independent of current in a wide range
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 37
gm/ID and transistor size
ID=mCox(W/L).f(VG, VS, VD)
S
Dfnorm
ox
Dnorm
Dnormnorm
D
m
I
IiI
LWC
II
LW
IIf
I
g
)/(
)/( I
m
When short channel effects are significant: L,If
I
gnorm
D
m
When short channel effects are not significant:
10-10
10-8
10-6
10-4
10-2
0
5
10
15
20
25
30
ID/(W/L)(A)
gm
/ID
(1/V
)
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 38
Design Methodology: gm/ID key variable
0
10
20
30
40
1.E-12 1.E-10 1.E-08 1.E-06 1.E-04
ID(A)
gm
/ID
(1
/V)
10-12
10-10
10-8
10-6
weak inv.
mod. inv.
strong inv.
1/nUT 2/GVO
Circuit Performance Transistor Operating Mode
Transistor Sizing
gm / ID
ID=mCox(W/L).f(VG, VS, VD)
g
If I
I
W L
II
C W L
m
Dnorm norm
D
normD
ox
I
( / )
( / )m
[Silveira, Flandre, Jespers, IEEE JSSC 1996, P.Jespers, Springer, 2010]
gm.vi gdVi
VO
CL
ID
VDD
CL
Vi VO
Ag
IV
g
C C
g
IIm
D
A
m
L L
m
D
D0
1
2
1
2 fT
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 39
W/L C gm
Optimum of Power Consumption
10-10
10-8
10-6
10-4
10-2
0
5
10
15
20
25
30
ID/(W/L)(A)
gm/ID
(1/V
)g
m/I
D (
1/V
)
ID/(W/L) (A)
Weak inversion: IDeVG/(n.UT)
Moderate inversion
Strong inversion (ID(VG-VT)2)
gm/ID ID
Usually an optimum exists in moderate inversion
• Working towards WI
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 40
Example Intrinsic Amplifier: Power Optimum
0 5 10 15 20 2510
-5
10-4
gm/ID (1/V)
ID (
A) 0 5 10 15 20 25
100
101
102
103
104
gm/ID (1/V)
W1 (
um
)
fT=10MHz, CL=3pF, L=2mm, tech: 0.8mm
V
vi
vo
CL
ID
DDV
vi
vo
CL
ID
DD
vi
vo
CL
ID
DD
0 5 10 15 20 252
4
6
8
10
12
gm/ID (1/V)
CLto
t (p
F)
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 41
Example Intrinsic amplifier 0.8um, CL 3pF
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E+00
0 5 10 15 20 25 30
gm/ID(1/V)
ID(A
)
100kHz
1MHz
10MHz
100MHz
1GHz
M.I. optimum
W.I. optimum
S.I. optimum
10-10
10-8
10-6
10-4
10-2
0
5
10
15
20
25
30
ID/(W/L)(A)
gm
/ID
(1/V
)g
m/I
D (
1/V
)
ID/(W/L) (A)
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 42 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 42
gm/ID in the nanometer and post CMOS era
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
0
5
10
15
20
25
30
35
ID/(W/L) (A)
gm
/ID
(1/V
) L=0.10,0.11,0.12,0.13,0.14
L=0.5L=1.0
L=4.0
W=10um,L(um)VDS=0.6V
B. Sensale-Rodriguez et al, accepted for presentation at IEEE SubVt 2012, joint work with U. Notre Dame, Indiana.
Derived based on data from P. Jespers, The gm/ID Methodology a sizing tool for low-voltage analog CMOS circuits, Springer, 2010, extras.springer.com
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 43 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 43
Outline
I. System: Active Implantable Medical Devices Today
II. Transistors and Circuits: Analog Design for ULP.
Transistor Modeling.
Design Methodology.
III. Circuit Techniques: Implementation of AIMDs blocks
IV. Conclusions and Prospects
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 44 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 44
ULP Analog Signal Processing: 1) RC Active Filter
Limited by values possible to integrate: up to k o M (special process) and 100s pF
Large spread in absolute values of integrated components
=> Drawback: need for external components ..., but ....
Low pass filter
s.C.R1
RR
v
v
2
1
2
in
o
VoVin
+
-
C
R1
R2
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 45 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 45
ULP Analog Signal Processing: External components should always be avoided ?
A few are required to avoid single fault risks.
Full integration might be paid in terms of consumption in order to accomodate less precise components
1 Ah = 114 mA.year 11.4mA 44mm3/ 100nA
10 year service life 5cc battery
0805
0603
0201
0402 SMT components up to 10M and 15mF
0402 SMT => 1mm x 0.5mm x 0.35mm = 0.18mm3
Considering PCB, IC package pin, routing => 2 - 5 mm3
Size and Consumption are linked through Battery size
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 46 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 46
ULP Analog Signal Processing: 2) Switched capacitor filters
1/R2.C = fclk.C2/C
+ precise, + large time constants possible, + fully integrated
- op amps consumption, - antialiasing
VoVin
+
-C
R1
R2
VinVo Vin
Vo
+
-
R1
1
+
-
C1
2
21
VinVo
2
+
-
C11
C
2 1
1
C2 22
1
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 47
ULP Analog Signal Processing: 3) Gm-C Filters
v+
v-
+
-
gm io = gm(v+ - v-)
vinVo
+
-
gm
C
+-
gm
VoVin
+
-
C
R1
R2
R=1/gm => 1/R2.C = gm2/C => spread
=> on-chip automatic tuning
+ large time constants possible
- input linear range requirements for transconductors
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 48 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 48
Example of modules: Pacemaker Activity Sense
Objective:
E.g. Activity indicator: 3s Average of the absolute
value of acceleration in the 0.5 - 7 Hz band.
Sensor 3s Averaging
Amplifier / filter
Ideal Rectifier
Amplitude: tens to hundreds of mV
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 49 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 49
Accelerometer Signal Conditioning (1): Amplifier / Bandpass filter
High pass
characteristic
Vs
Vf
Input signal
Feedback signal
Double input symmetrical OTA (DDA)
Vo
Vo=A1Vs+A2Vf
ISCAS 1998
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 50
Accelerometer Signal Conditioning (2): Layout and results
Gain 2900
Equivalent input noise (mVrms)
18
Consumption (mA)
3.4
Area (mm2)
1.82
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 51
Accelerometer Signal Conditioning (3): Results
0
20
40
60
80
100
120
140
160
180
200
0
20
40
60
80
100
120
140
160
180
200
0 50 100 150 200
dig
itiz
ed
ou
tpu
t o
f cir
cu
it
ca
rd
iac freq
.(p
pm
)
time(s)
actual cardiac frequency of healthy patient
simulated pacemaker frequency
circuit output
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 52
Accelerometer Signal Conditioning (4) : Gm-C implementation
A. Arnaud (UR), C. Galup (UFSC), ISCAS 2004
FiltroFiltro--Amplificador 0.5Amplificador 0.5--7Hz7Hz
CC11=550p=550p
VVBiasBias==
700mV700mV CC22=50p=50p
VVOutOut11
++
GGm1m1
GGm2m2
GGm3m3
VVININ
SensorSensor
VVlinlin==5mV5mV
CC33=50p=50p
VVOut2Out2
++
GGm4m4
GGm5m5
GGm6m6
VVlinlin==500mV500mV
CC44=250p=250p
G=385G=385
Gm4=21nS
Gm5=2.5nS
Gm6=89pS
Ganancia 2a:
G2=8.3
Gm4=21nS
Gm5=2.5nS
Gm6=89pS
Ganancia Preamplificador:
G1=46.4
IDD= 290nA
Equivalent
Input noise:
2.1mVrms
Gain: 390
Fully
integrated
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 53 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 53
Example of modules: Neural Recording Amplifier
• Objective: Signal detection from e.g: cuff electrodes or cortical electrodes arrays
• Requirements:
• 0.5mVrms - 2mVrms noise
• BW: 300Hz – 8kHz
• High CMRR (particularly in Cuff)
• Block high DC offsets (100mV or more) due to electrode/tissue contact
• Negligible DC input current
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 54 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 54
Example: Cuff Electrode Recording in Neurostep
Hoffer et al, IFESS 2005
Hoffer et al, US Patent 5,824,027 / 1998
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 55
Example: Cortical Recordings
Harrison, Proc. IEEE, July 2008
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 56 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 56
Neural Amplifier Front End (1): Capacitive Feedback
• Inversion region for noise / power optimization: e.g. input pair weak inversion, current mirror active load: strong inversion
• CMRR limited by capacitor matching.
Harrison et al, IEEE JSSC, June 2003
Gain 40 dB
BW 0.13 Hz / 7.5 kHz
Itotal 16 mA
NEF 3.8
vnoise rms 2.1 mV
CMRR > 42 dB
MOS –Bipolar Pseudoresistor (100s Mohms equivalent)
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 57
Neural Amplifier Front End (2): DDA Based
J. Sacristán, T. Oses, IFESS 2002,
Another DDA Based Scheme: M. Baru, U.S. Patent 6.996.435, 2006
• High CMRR
(Given by Input Differential Pair)
• Both Differential
Pairs contribute equally to Input Noise (hence to area and consumption)
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 58
Neural Amplifier Front End (3): “Asymmetrical” DDA Based (I)
P. Castro, F. Silveira, ISCAS 2011
• Effect of noise (and
hence consumption and area) of Gm2 greatly reduced while keeping high CMRR (given by input differential pair)
• Gm2 less effective in compensating input offset and DC components => Output DC and high pass characteristic fixed by local feedback at the output
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 59
Neural Amplifier Front End (4): “Asymmetrical” DDA Based (II)
Spec Castro,
ISCAS 2011
Harrison,
JSSC 2003
Wattapanitch,
TR. BIOCAS
2007
Sacristan,
IFESS 2002
Architecture Asym. DDA Capacitive Capacitive DDA
A (dB) 48 40 41 80
NEF 4.2 3.8 2.7 53.4
Itotal(mA) 16.5 16.0 2.7 180
vi noise
(mVrms)
2.4 2.1 3.1 7.6
CMRR > 107 > 42 > 66 90
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 60 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 60
Outline
I. System: Active Implantable Medical Devices Today
II. Transistors and Circuits: Analog Design for ULP.
Transistor Modeling.
Design Methodology.
III. Circuit Techniques: Implementation of AIMDs blocks
IV. Conclusions and Prospects
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 61 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 61
Prospects: Digital vs. Analog
• Theoretical limits of power consumption for Analog and Digital Signal Processing
• Analog better for low S/N, but the border is moving ...
• “Digital” pacemaker already present in marketing
Scaling
Source: E. Vittoz
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 62
Prospects: Analog ULP and AIMD
• Intense growth of applications / therapies on development and reaching the market
• Broad Analog / Circuit research area:
• Sensing
• Stimulation, Power Management / Battery Recharge, Communication, …
• Once very specific area, now wider (wireless sensor networks, body area networks, portable devices, energy scavenging devices, RFID, ...).
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 63 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 63
Prospects: AIMDs Brain Computer Interface
Set. 2000, Nicolelis, Duke University
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 64 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 64
Prospects: AIMDs Brain Computer Interface
Mar. 2002, M. Serruya, J. Donoghue, Brown University
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 65 F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 65
Prospects AIMDs: Brain Computer Interface
July 2004: Pilot FDA trial started by spin/off company of Brown Univ., several tetraplegic patients implanted.
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 66
Some Conclusions
•ULP ICs for AIMDs: Each nA counts => Methodology and Optimization
•AIMDs: Very broad field in strong expansion Many R & D opportunities Microtechnology is often the enabling factor.
•AIMDs: Price is not the main concern, but application and performance Suitable for developments with lower volume
productions than in other areas High investment associated with long
development cycles, qualification, clinical testing and regulatory aspects.
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 67
Microelectronics Group – IIE Universidad de la República
More Information
iie.fing.edu.uy/vlsi
Acknowledgements
• IEEE CASS
• CCC Medical Devices, NanoWattICs
• Members (present and past) of Microelectronics Group, UR
F. Silveira, Univ. de la República, Montevideo, Uruguay IEEE CASS DLP 68
Thank you !