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BME305 Coursework Aassignment (with O

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BME305 Coursework Aassignment (with O. Escalona, 2022)

Analysis Practice Assignment for Group B only

Title: Basic op-amp circuitry for recording the electrocardiogram (ECG).

Learning outcome

Gain hands-on experience in analysing basic biopotential amplifiers electronics circuitry.

Background

Sequences of rhythmic contractions and relaxations of the cardiac muscle (also known as heartbeats) are the driving force behind the circulation of blood in the human body. The mechanical activity of the cardiac muscle generates a time varying dipole electric field that extends throughout the human body. The presence of such electric field on the torso gives rise

to electrical potential differences on the surface (skin) of the chest and limbs. A small potential difference (the peak value is typically 1mV) between two points on the chest may be recorded using ECG electrodes that are adhered to the skin. An ECG is a recording of such a dynamic potential difference between two distant electrodes on the chest. ECG recordings are utilised by clinical personnel for the non-invasive check of the heart rhythm.

The differential input terminals of ECG recorders typically contain a biopotential amplifier

Stage (to account for the low magnitudes of the recorded potential differences) and a filtering stage. In this circuit analysis practice, we will study a basic ECG front-end by

utilising a 3-Op-Amp instrumentation amplifier stage and a band-pass filter stage. The

circuit diagram of the ECG recording system is depicted in Figure 1.

The ECG amplifier circuit diagram

A A

100 nF

 

aa LA 10k >

 

RA PX it § 2MQ 1MQ

 

> 100k > Oscilloscope

 

END it oF | Vout

 

Figure 1. ECG front-end circuitry. 3-Op-Amp Instrumentation amplifier (green) and band-pass filter build-up using high-pass filter stage (red) cascaded by a low-pass filter (yellow) stage.

Analytical Practice Study

In the ECG amplifier circuit of Fig. 2, consider a differential input signal between terminals LA and RA (LA-RA)

having a peak-to-peak (p-p) amplitude of 1 mV, as provided by an ECG simulator signal generator.

1) Analysis of the p-p amplitude of output waveforms: calculate the expected p-p amplitude of the waveforms

at Vout, Vo1 and Vo2 (with respect to ground), at the circuit points shown in Fig. 2.

2) Now change the value of R2 to 20kΩ and repeat the calculations indicated in (1).

3) Restore the value of R2 to 10kΩ, as it was originally set in (1). Now change the value of the two R4 resistors

to 200kΩ and repeat the measurements indicated in (1).

Figure 2. The ECG amplifier circuit indicating waveform amplitude analysis points (Vo1, Vo2 & Vout).

Assignment Report structure parts to work and respective marks (Total = 100 marks)

a) Cover page with title and name. An introduction page; on the topic of the analysis practice and about

related op-amp circuit analysis theory used. (10 marks)

b) Provide a summary account about the ECG amplifier stages of voltage gain expressions for the

particular 3-Op-Amp Instrumentation amplifier configuration use (green block in Fig. 2), and present

worked calculations for voltage gain at the different stages: dual input stage with the various values of

R2 used, the differential stage with the various values of R4 used and the band-pass filter stage gain.

(20 marks)

c) Present the calculated values of output waveforms p-p amplitude in activity (1), assuming a p-p

amplitude of 1 mV for the differential input signal (LA – RA). (15 marks)

d) Present the calculated values of output waveforms p-p amplitude in activity (2), assuming a p-p

amplitude of 1 mV for the differential input signal, and discuss the results in comparison to the results obtained in (c), and comment on the effect of the R2 change with regard to waveforms p-p amplitude changes with respect to values calculated in (c). (15 marks)

e) Present the calculated values of output waveforms p-p amplitude in activity (3), assuming a p-p amplitude of 1 mV for the differential input signal, and now discuss the results in comparison to the results obtained in (c), and comment on the effect of the R4 change with regard to waveforms p-p

amplitude changes with respect to values calculated in (c). (15 marks)

f) Calculate the high-pass (fCH) and low-pass (fCL) cut-off frequencies of the passive, 1st order, band

pass filter used in the ECG amplifier circuit of Fig. 2. (15 marks)

g) Conclusion paragraph. (10 marks)

Submission: All analytical practice reports are individual. Submit this assignment report in the module’s Bb

Assignments area, by Thursday of Week-12, 14/April/2022, before 6:00 pm.

Marks scheme: As indicated on each part of the report structure. Maximum mark is 100%