Q B1 (a) In the op-amp based amplifier shown in Fig

Q B1 (a) In the op-amp based amplifier shown in Fig. Q•B1(a), the values of  and R4 are as indicated Ri, R2, R3 .

witn any variables involved in your solutions. ,...atiuris without presenting the working out will not be accepted. „sun. Indicate any assumptions SECTION B Answer TWO questions from this section

If Vi = 1.2V and V2 = 3.2V, determine the value of Vo, and hence, specify the differential voltage gain, ADM. If V1 = V2 = Vcm = 5.0V, determine the value of Vo, and hence, specify the common mode voltage gain, ACK

= 20 kl) R2= 100 kO R3 = 20 kO R4= 120 kC)

Fig. Q.B1(a)

vo

(9 marks)

(b) It is required to generate a single pulse waveform (Vtrigg) of 8 Volts amplitude (peak-to peak) and 12 ms duration to trigger a defibrillator using the circuit in Fig. Q.B1(b). Assuming R = 100 kO and of R2 = 3 kO calculate values of Ri and C. Also assume +/- VsAT = +1- 12 V.

Fig. Q.B1(b)

9/13

Ri Vtrigg

(c) High-frequency ECG analysis in the ST-T segment of an ECG signal recording

requires the analysis of signal components above 80 Hz and below 500 Hz. Design a first order band pass passive filter to accommodate this specified frequency bandwidth. Sketch the circuit configuration. You may use an op-amp buffer stage in your circuit design.

(8 marks)

Total 25 marks

Q.B2 (a) The 3-0pAmp Instrumentations Amplifier in Fig. Q.B2(a) is the front-end stage of an ECG amplifier, having the indicated values of resistors. Briefly explain the role of op-amps Ai and A2 and determine the voltage gain at this Stage-1: AStage-1 t (V02 — V01) I (V2 - V1)1; assuming all resistors and op-amps are ideal and the resistors in the circuit have the exact values as indicated. Also, determine the voltage gain of the difference amplifier stage (Stage-2): AStage-2 Vo I (Vo2 - Vol ), implemented by A3. Then, specify the total differential voltage gain of the 3-0pAmp amplifier (cascaded Stage-I and Stage-2): ATotal = [ Vo I (V2-1/1)1.

R1 = 60 ko ; R2 = 20 k0 ; R3 = 10 ; R4 = 80 kn

Al vi RI

R1

VO I

R3

R3

V02

R4

A3

—0

77-

Fig. Q.B2(a)

Vo

(8 marks)
(b)

The 50Hz interference current (lo) pickup by capacitive coupling (Ci and C2) in the two input leads of an ECG amplifier is 5 nA(that is, ID= IDi= ID2= 5 nA) and the two skin-electrode (ZSE) impedances imbalance (AZsE) is 20 kn. Estimate the differential noise signal that would appear at the input of the ECG amplifier, due to the electrodes impedance imbalance.

(5 marks)

(c) In an ECG amplifier, the 50Hz interference current component, IDB, due to body capacitive coupling (CB), is 0.3 pA (i.e., IDB= 0.3 pA), the electrodes impedance imbalance (LZE) is 30 kn and the right-leg electrode impedance (ZRL), connected to the ECG amplifier ground terminal, is 80 kQ (that is, ZRL = ZG = 80k n). Estimate the common mode noise voltage in the body (Vcm), and the differential noise signal that would appear at the input of the ECG amplifier if the amplifier input impedance (Z1N) presented at each input terminal is 8 M. (6 marks)

(d) If in an ECG amplifier the 50 Hz interference current (IDB) pickup by capacitive coupling (CB) of the body is 0.6 pA, and the right leg electrode impedance is 50k0. Determine the equivalent value of the right leg electrode impedance (RRL) if in Fig. Q.B2(d) the driven right leg noise reduction circuit, with Ra =20 kn and Rb =20M0, is used. (6 marks)

1 

Rg

IDB RRL Right Leg

Fig. Q.B2(d)

R A3

Vo

Total 25 marks