Principles of Bioelectronics Design Lecture #1

Transcription

1 Principles of Bioelectronics Design Lecture #1

2 3.5- יסודות תכן ביו-חשמלי נקודות זיקוי מרצה: פרופסור ראמז דאניאל בניין אמרסון קומה 7 שעות קבלה:לפי תיאום מראש ramizda@bm.technion.ac.il מתרגל : ירון רם בודק תרגילים: לונא ריזק עבודות בית : 8 -הגשה חובה 10% תרגיל מחשב: 2- הגשה חובה 10% בוחן מגן 20% בחינה- 60% אתר הקורס: מקצועות קדם: תורת המעגלים החשמליים מקצועות מקביל: אותות ומערכות חומרי לימוד: Medical Instrumentation Application and Design, 4th Edition, John G. Webster 2009 Foundations of Analog and Digital Electronic Circuits, 1st Edition, Agarwal & Lang Physics of Semiconductor Devices by S.M. Sze

3 3.5- יסודות תכן ביו-חשמלי נקודות זיקוי Syllabus: 1. General introduction 2. Introduction to semiconductor 3. PN Junction 4. Diode 5. MOS capacitor 6. MOS Transistor 7. Circuits - Small signal analysis 7. Circuits MOSFET amplifier 8. Circuits - MOSFET advanced 9. Differential amplifier 10.Negative feedback 11.Digital circuits Devices Analog Design Digital Design

4 Why should we study electronic devices and circuits imaging capsule Electroencephalography (EEG) Glucose biosensor Electrocardiogram potential (EKG) Ultrasound

5 Why should we study electronic devices and circuits Simply it is the best way to measure and display biological signals Biological Signals are often analog continues in time Computation and signal processing in computers are often digital discrete in time OFF State 0 ON State 0

6 Analog and Digital Biological Signals are often analog continues in time Frequency Response Every signal can be represented as a Sum of periodic signals with different frequency and amplitude (linear operation). The amplitude value is Fourier Transform

7 Sampling the analog signal (f s BW) Analog and Digital Digitized signal sequence of numbers that represents the magnitudes of signal samples Computation and signal processing in computers are often digital discrete in time

8 Biosenors Converts Biological signal to electrical signal. Requirements: 1. Specificity 2. Can track the changes in the biological signals, faster than the biological signal (BW Biosen >BW Signal ) 3. Sensitivity 4. linearity 5. Noise Transfer function of sensor

9 Biosenors Linearization - Small Signal Analysis V = f x v = df dx XD X For example: V = V 0 e x/x 0 V = 1 X 0 V 0 e X D/X 0 X Slope = V X = V D X 0

10 First Order Biosensor: Biosenors R and C are patristic I R = V R, I B = I R + I C I B = f x C dv dt + V R I C = C dv dt = f x dv dt = f(x) C V RC τ = RC For constant I B : V t = I B R(1 e t τ ) V t = τ = I B R 1 e 1 = 0.63I B R

11 Biosenors First Order Biosensor: Frequency response For constant I B : dv dt = I B C V τ Fourier transform jωv = i B C v τ v jωτ + 1 = R i B v(ω) = R i B(ω) (jωτ + 1) v(ω = 0) = R I B v(ω = ω c ) = R I B 2 v(ω ) = 0 v(ω) = R I B ω ω c ω c = 1/τ

12 Biosenors First Order Biosensor: Frequency response v(ω) = R I B ω ω c ω c = 1/RC v(ω = 0) = R I B v(ω = ω c ) = R I B 2 v(ω ) = 0 Low pass filter: every input signal with frequency higher ω C will be cut-off log 1/

13 Low pass filter v(ω) = R i B(ω) (jωτ + 1) Biosenors v ω = i B (ω) H LPF (ω) sin ω b t Fourier transform δ(ω ω b ) ω b > ω c V=0 ω b < ω c V=Biological Signal Therefore it is important to design the biosensor physical parameters to set the value of RC (e.g., dimensions )

14 Biosenors First Order Biosensor: Frequency response We can arrive to the same results by KCL and KVL The impedance of R does not depend on the frequency (Z R =R) The impedance of C depends on the frequency (Z C =1/jωC) V = I B (Z R Z C ) V = I B Z R Z C Z R + Z C 1 R jωc V = I B R + 1 jωc V = I B V = I B R jωrc + 1 R (ωrc) 2 +1 V = I B 1 R jωc jωcr + 1 jωc

15 Biosenors -Photodiode Biosensor converts one type of energy to electrical energy Photodiode: is pn junction that converts light to electrical energy Light increases the dark current C dv dt + V R = I Light I Diode I Diode = I dark (e qv KT 1) Low pass filter R = dv di = KT q I C is the junction capacitance

16 Biosenors - Piezoelectricity Biosensor converts one type of energy to electrical energy Piezoelectricity: convert mechanical energy to electrical energy Measure pressure and ultrasound waves It is reversbile: an applied mechanical stress will generate a voltage and an applied voltage will change the shape of the solid by a small amount (up to a 4% change in volume). Convert deflection/displacement to charge generator: q Kx K is a constant depends on the material X is a deflection R Sensor leakage resistance C Sensor capacitance C 0 r A x Piezoelectric crystal (quartz)

17 Biosenors - Piezoelectricity Changes in x cause to change in the charge and producing a current. Convert charge generator to current generator: I B = dq dt = K dx dt C dv dt + V R = K dx dt dv dt = K dx S dt V τ K s = K/C, sensitivity, V/m = RC, time constant Fourier transform jωv = K S jωx(ω) v τ v(ω) = K Sjωτ 1 + jωτ x(ω)

18 Biosenors - Piezoelectricity v(ω) = K S ω ω c ω ω 2 c + 1 x(ω) High Pass filter (HPF) ω b < ω c V=0 ω b > ω c V ~ x K s = K/C, sensitivity, V/m = RC, time constant

19 Electrochemical Biosenors Convert biochemical reactions to electrical signal Electrochemistry: interfacing electrode with electrolyte Oxidation: Ions that lose their electrons Reduction: Ions that gain new electrons

20 LPF Electrochemical Biosenors Equivalent electrical circuit of electrochemical cells R ct : Charge transfer resistance due to transfer of electrons from ions to electrode C dl : Double layer capacitor accumulation of charge in the interface between the electrolyte and electrode R S : series resistance electrolyte solution resistance Z eq = R s + R ct 1 + j ω R ct C dl

21 Amplifier An input signals (current/voltage) is amplified to a larger output signals (current/voltage) Features: 1. Linearity (wide linear range) 2. High Gain 3. Vin=0 Vout=0 4. High signal to noise ratio 5. Stability at time (One dominant half time) 6. Stable gain (not depend on circuit parameters, VDD, temperature )

22 Amplifier

23 Amplifier Voltage amplifier v out = A v v in V in input V out output Av voltage gain [db] R i is input resistance R o output resistance R S source resistance R L Load Resistance v in = v s R i R i + R S v out = A v v in R L R L +R O v out = A v v s A veff = v out v s R i R i +R S = A v R L R L +R O R i R i +R S 20 log A v [db] decibels R L R L +R O

24 Differential amplifier Amplifier V out = A (V in1 V in2 ) Reject common noise: V in = V in1 V in2 = V in1 + V in2 V in = V in1 V in2

25 Negative feedback Negative feedback loop: when the output of the system feed it back to control and reduce his activity Open loop equation: V out = A (V in1 V in2 ) Negative feedback loop equation: V in2 = β V out V out = A V in1 β V out V out = V in1 A 1 + β A Black s Formula β A>>1 V out =V in1 /β Negative feedback can increase the stability

26 Analog-to-digital converts

27 Noise accumulated in analog circuits noise hampers our ability to distinguish between small differences in value e.g. between 3.1V and 3.2V. Solution : Digital circuit

28 Digital circuits 1. Device of two states (OFF/ON) or (0/1) V out = V ON V off V in > V th V in < V th 2. Computation arises from logic functions (Boolean algebra) using basic logic gates: