bio-amplifiers-basics.pptx

What is Amplifiers?
 A n a m p l i f i e r, e l e c t r o n i c a m p l i f i e r o r
( i n f o r m a l l y ) a m p i s a n e l e c t r o n i c
d e v i c e t h a t c a n i n c r e a s e t h e p o w e r
o f a s i g n a l ( a t i m e - v a r y i n g v o l t a g e
o r c u r r e n t ) .
 B i o p o t e n t i a l A m p l i f i e r s a l s o c a l l e d B i o -
A m p l i f i e r s a r e s p e c i f i c a l l y d e s i g n e d f o r
p r o c e s s i n g o f B i o - e l e c t r i c s i g n a l s a s t h e y
a r e l o w i n a m p l i t u d e .

WHAT IS BIO-AMPLIFIERS?
It is an electrophysiological device, a variation of the
instrumentation amplifier, used to gather and increase the signal
integrityof physiologic electrical activity for output to various
sources. It may be an independent unit, or integrated into the
electrodes.

What is Bio-potential
Amplifier?
Amplifiers are an integral part of Electronic
devices and modern Instrumentation for
measuring Bio-potentials. As the name indicates,
Amplifiers are used to increase the signal
strength while maintaining high fidelity.
The measurements include voltages that are at
low levels and high source impedance.

Introduction
Bio-electric signals are generally low in amplitude.
Amplifiers that are specifically designed for
processing this type of Bio-potentials are known as
Biopotential Amplifiers.
The outputs from such amplifiers are used for
analysis and they show up as ECG, EMG or other Bio-
electric waveforms. These amplifiers typically process
voltages but in some cases they process current.

Introduction
The amplifier provides high impedance, high
CMRR and thereby minimizes loading effects.
This is the vital functionality of Biopotential
Amplifiers. For Biomedical applications, Bio-
amplifiers must meet the below mentioned
requirements in order to work incessantly.

Introduction
To measure Biopotential, electrodes are placed
on Human skin as shown in the Fig. 2. The
signals from the Electrodes pass on to the
Amplifier stage. Amplifier helps in minimizing,
eliminating most of the signals interfering with
the measurement of Bio-potentials and final
readout is obtained.

Fig. 2 – Schematic Representation of Biopotential Measurement

Basic Requirements for
Biopotential Amplifier
High input impedance. Typically, they range between 2
MΩ to 10 MΩ. Greater the impedance value, lower the
distortion of the signal.
Every Bio-amplifier must contain Isolation and
Protection circuits for safety purposes especially to
prevent patients from macro and micro-electric shocks.
Output impedance should be low to drive an external
load with minimal distortion.
Most Biopotential Amplifiers are differential.

Basic Requirements for
Signals are recorded using bipolar electrodes that are
symmetrically allocated.
CMRR (Common Mode Rejection Ratio) must be high as
they ride on a large offset signal and to reduce
interference from common-mode signals.
The gain must be calibrated for each measurement.
An ideal Bio-amplifier must be free from noise and
distortion.
A constant gain must be maintained throughout the
entire bandwidth range.

1..Thebio lo g ica l a m plifier sho uld ha ve a hig h input
impedance value.
2. .The range of value lies between 2 MΩ and 10 MΩ
depending o n the a pplica tio ns. Hig her im peda nce
value reduces distortion of the signal.
3. .When electrodes pick up biopotentials from the
hum a n bo dy, the input circuit sho uld be pro tected.
4.Every bio- amplifier should consist of isolation and
pro tectio n circuits, to prevent the pa tients
from electrical shocks.
BASIC REQUIREMENTS FOR
BIOLOGICAL AMPLIFIERS

WHY IS BIO AMPLIFIER
REQUIRED?
Generally, biological/bioelectric signals have low
amplitude and low frequency. Therefore, to
increase the amplitude level of biosignals
amplifiers are designed.

Types of Bio-
Amplifiers
1.Differential Amplifier
2.Operational Amplifier
3.Instrumentation
Amplifier
4.Chopper Amplifier
5.Isolation Amplifier

Mostly used bio-Amplifiers
1.Instrumentation
Amplifier
2.Isolation Amplifier

Differential Amplifier
These are used to amplify the
difference between the voltages
applied to its inputs. The circuits are
of two types.
Amplifiers built using Op-Amps.
Amplifiers built using either FET’s
(Field Effect Transistors) or BJT’s
(Bipolar Junction Transistors).

Differential Amplifier
Fig. 3 – Differential Amplifier Circuit

Operational Amplifier
These are multistage amplifiers
which are interconnected and
occupies minimal space even
though it consists of many
Transistors, Resistors, and FET’s.
They are available in the form of an
Integrated Circuit (IC).

Operational Amplifier
Fig. 4 – Symbol of Operational Amplifier

Instrumentation Amplifier
It consists of 3-amplifiers in the circuit. The
input to the amplifier is the output from the
Transducer.
A non-inverting amplifier is connected to
each of the input of the Differential Amplifier.
Non-inverting amplifiers are the ones on the
left side of the diagram.
The non-inverting amplifiers together form
the input of the instrumentation amplifier.

Fig. 5 – Instrumentation Amplifier Circuit

The third op-amp is called the difference amplifier and
is the output of the instrumentation amplifier. The
difference between the two input signals forms the
output Vout. V1 and V2 are the inputs to Op-amp 1 and
Op-amp 2 respectively.
A typical application of these amplifiers includes
Biomedical applications such as Biopotential Amplifier.
High gain and high impedance are attained using these
amplifiers which are crucial in medical instruments to
determine the health condition of an individual.

INSTRUMENTATION
AMPLIFIER
1.In biomedical applications, high gain and the
high input impedance are attained with an
instrumentation amplifier.
2.Usually, a 3-amplifier setup forms
the instrumentation amplifier circuit.
3.The output from the transducer is given as input
to the instrumentation amplifier.
4.Before the signal goes to the next stage, a
special amplifier is required with high CMRR, high
input
impedance and to avoid loading effects. Such a
special amplifier is an instrumentation amplifier,

CHOPPER
AMPLIFIER
Noise and drift are the two major
issues encountered when recording Bio-
potentials. Noise is caused by the
movement of the patient or due to the
recording device.
A DC Amplifier hits a sudden peak in
the output when the input is zero. A
Chopper Amplifier samples the problem
of drift in DC amplifiers.

CHOPPER
AMPLIFIER
Fig. 6 – Chopper Amplifier Circuit

ISOLATION
AMPLIFIER
These are also known as Pre-amplifier isolation circuits. It
provides electrical isolation for the safety of the patient. It
prevents accidental shocks and increases the input impedance
of the patient’s monitoring system.

hospital.
1.Isolation amplifiers are known as Pre-
amplifier isolation circuits.
2.An isolation amplifier increases the input
impedance of a patient monitoring system.
3.It also helps to isolate the patient from the
device.
4.Using the isolation amplifier prevents
accidental internal cardiac shock.
5.It provides up to 1012Ω insulation between
the patient and the power line in the
ISOLATION
AMPLIFIER

The electrical signals are
obtained with electrodes.
The signals received goes to
the amplifier block, where
signals amplification occurs.
After amplification, the signal
enters the modulation block.
When either it goes to the
isolation barrier, optical cable
or transformer can be used.
Isolation Amplifier

If in case of optical cable, modulator output
travels to LED.
The LED converts electrical signals into light
energy.
If the transformer acts an isolation barrier,
modulator output connects the primary winding of
the transformer.
Energy from primary transfers to the secondary
winding based on the mutual induction principle.
At the next stage, secondary output enters the
demodulation block.
Finally, the amplified demodulated signal is
obtained.
Isolation Amplifier

Various stages which represents Biopotential Amplifier
is shown in the Fig. 8. The Electrodes (Bipolar) are placed
on the patients skin which provide transition between the
ionic flow of currents in biological tissue and electronic
flow of current in the Amplifier.
The measurement of Bio-potentials is critical and due to
relative movements of electrode and tissue, it gives rise to
electrode offset potential and electrode/tissue
impedance.
Thus, two interference signals are generated which are
successfully eliminated at later stages of the amplification.
How does Biopotential Amplifier Work

The signal from the electrodes pass on to the pre-
amplifier stage which helps in minimizing,
eliminating most of the signals interfering with the
measurement of Bio-potentials.
High Pass Filter and Low Pass Filter eliminates
interference signals like electrode Half-cell potentials
and Pre-amplifier offset potentials. It also reduces
noise amplitude. Bio-signal should not be distorted
or attenuated and hence Filters are used.
How does Biopotential
Amplifier Work

Fig. 8 – Block Diagram of Stages of

In the Isolation Amplifier stage, galvanic decoupling of the patient from
the measuring equipment is served. It prevents Galvanic currents from
deteriorating Signal to Noise Ratio and provides safety to the patient from
electrical hazards. Transformer, Optical or Capacitive Couplers are used in
Analog Isolation Amplifiers, to transmit signal through the isolation
barrier. On the other hand, Digital Isolation Amplifiers use Voltage and
frequency converter to digitize the signal before it is transmitted.
Recording of the Bio-potentials in the last stage is done with electrical
systems which produce strong electrical and magnetic fields. Hence the
system is capacitively coupled and the current flows to the ground
electrode.
How does Biopotential
Amplifier Work

They are majorly used in medical
instrumentation systems such as ECG, EMG, CT
scan equipment, Patient hospital monitor.
They are also used in Electromyogram
integrator’s, Cardio tachometers, Vector
Cardiograph.
They are used in Bio-telemetry, Holter
Recorder and other devices to determine the
specific health condition of a patient.
Applications of Biopotential Amplifier

Monitored to understand heart health.
Displays ECG waveform.
Instrumentation amplifiers give accurate testing and measurement. They do
not require input impedance to be matched. This is the reason for using these
amplifiers for testing and measuring a wide variety of equipment.
Biopotential Amplifiers are very easy to use and stable. These are ideal for
long term usage.
They don’t necessarily depend too much on various factors that influence
the output at the later stages. The Instrumentation Amplifiers work with just
input.
The Biopotential Amplifiers are highly scalable.
Even a small input can be amplified to a greater extent at the input level.
Advantages of Biopotential Amplifier

Sometimes, there could be minor
distortion or noise in the output.
The system often depends on
special cables to remove the noise.
Superimposing of original is the only
concern when the noise gets
transmitted for a long-range.
Disadvantages of Biopotential Amplifier

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