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Answer quest 7 a | an - i | lon PUrpose of cach Oar, ste Made

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Answer quest 7 a | an - i |
lon
PUrpose of cach Oar, ste
Made. Als ach Step made Pby-step, Presenting i
Simply antwenn Indicate the unis the Solution of the four Working out and briefly stati
ng Questions without ®SSOciated with any variabhe neon Indicate any assumptions
Gy Presenting the Working out will Not be aces cotutions.
gical tissues are th ,
and reactive components = Complex, anisotropic conductors with resistive
Such a tissue with all the FI9.Q.A3.a below shows the distribution of cells in
(CM), extra cellul relevant components shown including cell membrane
ular fluid (RE) and intra-cellular fluid (RI),
C©) Cy Membrane
‘ Extra-Cellular
Fluld (ECF)
OC
Intra-Celfular
Fluid (1CF)
Fig. Q.A3.a: Schematic of cell distribution inside a
tissue
(i) For such as tissue, utilising the concepts of impedance, describe and
draw the equivalent electrical circuit showing the series, parallel combination of
components described by CM, RE and RI. (2 marks)
(ii) |§ What path the low frequency current will take and why? (2 marks)
(ili) | What path the high frequency current will take and why? (2 marks)
=) how that the voltage output (VO) of the circuit shown in Fig. Q.A3.b may be
expressed as, Vo =k. Vin where VO is the output voltage, k is a constant and
Vin refers to the input voltage. Note: block X symbolises a multiplier circuit.
R “
__ x fe
V. R
0 _{ Vo
Vs
Fig. Q.A3.b (10 marks)
(Question A3 continues, please turn the page)
TS

nswer questions cle
surpose Of each step mac Pby-step, Presenting in detail
made. Also, clearly indicate the units ine Solution of the given questin’ saat and briefly stating the
ssoci ; t
Simply answering questions without presenting they aiables Involved in you an aon
6.A3 g out will not be accepted.
(c) or the com ici; |
te parator circuit shown below (Fig. Q.A3.c), a sinusoidal input signal
Ww - ,
a peak-to-peak voltage (Vp) of 10 V and a frequency of 1 Hz is applied to
the non-inverting terminal of an op-amp. Assuming that the input signal
frequency is well below the slew rate limit, describe and draw what the
comparator output be for the following situations.
(i) Vref = 0V (2 ne
. 2 marks
(ii) Vref = 5 V , in
Assume values of +VCC as +12V and -VCC as -12 V, with the corresponding
output saturation voltages of +Vsat of +11 V and -Vsat of -11 V.
e +Vec
8V Min Vs
, — t
V,
Veet Vo
° 48 —Vi¢
Fig. Q.A3.c
ion values £12 V, and a
A Schmitt trigger circuit is required to have saturation v lacey circuit
” hing thresholds (UTP and LTP) of #2.7 V. For ine Schmitt ngs th
itchin hat the
“ . Figure Q.A3.d determine the values of Rx and Ry such t
wn in —_— tput
e tioned conditions are fulfilled. Also, sketch the input-oulp
above- ment et-triqaer
characteristic of such an inverting Schmitt-trgger.
+Vec
Vin M Vo
-_
Rxl
(5 marks)
Fig. QA3(4)
° [Total 25 marks]
8/13

; oe, =
, enting in detall your work
Answer ques en 5 a Hae eatey ‘solution he the given ‘question Indicate any devunng ne
purposs ° nearty indi cate the units associated with any variables involved in your solutions ptions
oa ply 3 nowe ring questions without presenting the working out will not be accepted. .
Q.A2
(c) (i) The circuit shown below is intended to act like a cascade in which the leftmost
portion of the circuit produces the natural log (In) of the input voltage (Vin). In
the inverting logarithmic amplifier shown in Fig.Q.A2.c, the bipolar junction
transistor (BJT) collector current ic is a function of the base-emitter voltage
(Vee) and reverse saturation current (leo) which is given by:
V pg = 0.0257 Ln)
beo
_
Ri ‘ 2 le
—_
— R2
@ In
Vo V,_final
7 =
Fig. Q.A2.c
if the parameter feo has value of 0.1 pA , determine the value of the resistance
R14 in order that Vo = - 0.0257 Ln(Vin). Note: Ln represents natural log.
(6 marks)
(il) Design (i.e. calculate the values of R2 and R3) the following inverting
amplifier stage to be cascaded after the natural logarithm amplifier, as shown
above in Fig.Q.A2(c), in order to correct the final output to be Vo_final = 2-L{(Vin),
where Ln is the natural log.
(6 marks)
[Total 25 marks]
6/13

Th ookl
7 ” on me circuit of Figure Q.A3a Vit) is a co
nstant j
/ alculate values of R and c for Volt) to be " meu Of 1.5 V, starting at t = 0,
while the capacitor CUTTent, ict), is a & ramp with a slope of - 0.6 Vims,
(= 15 mA). Assuming that the ca eee current of 15 MA (ie.,
and that the sa turated val Pacitor C is initially discharged, V,(; « 0) = OV.
a, Values of Vo(t) are +Ves = +14V draw a sk
indicating the time he sketch of Vo/t)
wnen the output reaches the saturation level.
Cc
re
R +> -
Ve
ot
V.{t)
Figure Q.A3a
(9 marks)
s (b) The generation of a single pulse waveform (Vo) of 8 ms duration is required to
trigger a defibrillator using the circuit below. Assuming R = 15 kQ, Ri = 10 kO
and R2 = 5 kQ and supply limit voltage +Vsar = +14 V, calculate the value of C.
Ve
D C
R,
Ry
(8 marks)
6
es on the next page, please turn the pag
n A3 continu
(Questo 6st

Before the digitisation process of a recorded ECG signal, high-frequency
signal components above 150 Hz must be eliminated, and the filtered ECG
signal requires amplification at a voltage gain of -8 V/V. To achieve this signal
conditioning process, the first order active low-pass filter circuit below is used.
if the value of R2 is set to 30 kQ, determine the required values of Ri and C for
the above proposed signa! conditioning process.
Signal conditioning
process R,
Ry aie Digitisation
Sek a process
ECG Seer one:
woe
(8 marks)
WM