The three measured ECG signals, on Figure , are respectively from the Instrumentation Amp, opto-coupler, and filter. The circuits function very well so that the three signals are almost identical to each other. Measuring different region of the heart will obtain different ECG signals.

1. DEPARMENT OF ELECTRONICS ENGINEERING
SUBJECT:-ANALOG SYSTEM DESIGN
ELECTROCARDIOGRAM
(ECG)
PREPARED BY:-
Himanshu.v.Gawande-55
GUIDED BY:- 5th semester SEC-A
BRANCH-ELECTRONICS
PROF. S.N JOSHI

2. INTRODUCTION
• WHAT IS ECG?
 A technique of recording bioelectric currents generated by the heart.
 It records any problems with the heart’s rhythm, and the conduction
of the heart beat through the heart which may be affected by
underlying heart disease.
• WHY IS ECG USED?
To check how well medicines are working and whether they are causing
side effects that affect the heart.
-To check the health of the heart when other diseases or conditions are
present such as high B.P., high cholestrol, diabetes, etc..
-To assess if the patient has had a heart attack or evidence of a
previous heart attack.
-To observe the effects of medicines used for coronary heart disease.
-To see if there are too few minerals in the blood.
-To diagnose poor blood flow to the heart, heart attack and
abnormalities of the heart.

3. CHARACTERISTICS
• The ECG signal consists of low amplitude voltages in the presence of
high amplitude offsets and noise.
• The large offsets present in the system are due to halfcell potential
developed at the electrodes
• Ag/AgCl(Silver-silverchloride) is the common electrode used in ECG
systems and has a maximum offset voltage of +/- 300 mV.
• -The actual desired signal is +/- 0.5 mV superimposed on the
electrode offset.
• In addition, the system also picks up the 50/60 Hz noise from the
power lines which forms the common mode signal.
• The amplitude of the power line noise may be very high . So, it has to
be filtered.

4. PRINCIPLE OF ECG
• The ECG device detects and amplifies the tiny electrical changes on
the skin that are caused when the heart muscle depolarizes during
each heartbeat.
• It can give information regarding the rhythm of the heart (whether or
not the electrical impulse consistently arises from the part of the heart
where it should and at what rate), whether that impulse is conducted
normally throughout the heart,
• It can also give information regarding the balance of salts
(electrolytes) in the blood (e.g. hyperkalaemia) or even reveal
problems with sodium channels within the heart muscle cells .
• It is one of the key tests performed when a heart attack (myocardial
infarction or MI) is suspected; the ECG can identify if the heart muscle
has been damaged in specific areas, though not all areas of the heart
are covered.

5. AMPLIFIERS IN ECG
• ECG signals vary from the microvolt to the millivolt range. Due to this
small range, the signals measured need to be amplified in order to
be better interpreted.
• Typical biopotential amplifiers have high input impedance and are
designed for safety first. This is due to the fact that the signal
amplified is being drawn from a living organism so precautions must
be taken in order to prevent macro and micro shock.
• Isolation and protection circuitry are used to limit current through
electrodes to safe levels.
• The output impedance of the amplifier should be very low to drive
any external load with minimal distortion. Again, due to the small size
of the signal, the gain should be large.

6. •The amplifiers should have a high common mode rejection ratio to
eliminate large offset signals. Finally, most biopotential amplifiers are
differential.
•Differential amplifiers are used to make sure that noise are not amplified
thus yielding . Thus combinations of differential amplifiers are used to
construct what is called an instrumentation amplifier.
Basic Instrumentation Amplifier

7. FILTERING
ECGs are subject to many different kinds of noise internally and externally.
These artifacts can be filtered digitally
as well as through analog practices.
For example, the analog band stop filter
shown in figure can be used to
modulate 60 Hz noise from power lines
based on what resistor,
capacitor, and inductor values
are chosen.
Different types of noises are:-
•Baseline wander(low frequency noise)
• Power line interference(50Hz or 60 Hz noise
• Muscle noise
Second order band stop
filter

8. ECG artifacts

9. • An ECG can show damage to the heart.
• How fast your heart is beating and the beating in normal rhythm .ECG
helps to Show the effects of drugs or devices used to control the heart.
• An ECG can show the size and position of your heart chambers.
LIMITATIONS
• A good ECG reading does not preclude having the underlying heart
disease and other symptoms, such as chest pain, must be taken into
account and further evaluation may be required.
• Not all heart problems will show up on an ECG. A prime example is
vulnerable plaque (a form of atheroma). which is a major cause of
heart attacks.
• False positives and false negatives are common among clinical tests. A
doctor has to weight all the evidence prior to making a diagnosis.
APPLICATIONS

10. WORKING OF ECG
• ECG machines use electrodes to convert the ionic signals from the
body into electrical signals to be displayed and used for data analysis.
However, due to the size of the signals and outside noise, ECG requires
amplification and filtering to produce high quality signals.
• An ECG’s job is to amplify the small signal measured from the heart as
well as to filter outside and internal noise. The amplification is mainly
implemented through a differential amplifier whereas filtering is
completed through common and differential mode filtering.
•

11. The heart is one of the most vital organs within the human body.
It acts as a pump that circulates oxygen and nutrient carrying blood around the body in order to
keep it functioning.
When the body is exerted the rate at which the heart beats will vary proportional to the amount
of effort being exerted.
By detecting the voltage created by the beating of the heart, its rate can be easily observed and
used for a number of health purposes .

12. A typical heart signal

13. Functional blocks of the ECG system

14. THE MEASURED
TRANSFER
FUNCTION OF
BAND PASS FILTER
ECG signals
CARDIAC cycle