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High CMRR Instrumentation Amplifier (Schematic and Layout) design for biomedical applications

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Instrumentation amplifiers are intended to be used whenever acquisition of a useful signal is difficult. IA’s must have extremely high input impedances because source impedances may be high and/or unbalanced. bias and offset currents are low and relatively stable so that the source impedance need not be constant. Balanced differential inputs are provided so that the signal source may be referenced to any reasonable level independent of the IA output load reference. Common mode rejection, a measure of input balance, is very high so that noise pickup and ground drops, characteristic of remote sensor applications, are minimized.Care is taken to provide high, well characterized stability of critical parameters under varying conditions, such as changing temperatures and supply voltages. Finally, all components that are critical to the performance of the IA are internal to the device. The precision of an IA is provided at the expense of flexibility. By committing to the one specific task of ...
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Diversity Techniques

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Diversity Techniques::
Fade margin on the transmitter path is not an efficient solution at all, and one alternate
solution is to take the advantage of the statistical behavior of the fading channel.
This is the basic concept of Diversity, where two or more inputs at the receiver are used
to get uncorrelated signals.

· Frequency Diversity
o Different frequencies means different wavelengths. The hope when using
frequency diversity is that the same physical multipath routes will not produce
simultaneous deep fades at two separate wavelengths.



· Space Diversity
o Deep multipath fade have unlucky occurrence when the receiving antenna is in
exactly in the ‘wrong’ place. One method of reducing the likelihood of multipath
fading is by using two receive antennas and using a switch to select the better
signal. If these are physically separated then the probability of a deep fade
occurring simultaneously at both of these antennas is significantly reduced.

· Angle Diversity
o In this case the receiving antennas are co-located but have different principal
directions.
· Polarization Diversity

o This involves simultaneously transmitting and receiving on two orthogonal
polarizations (e.g. horizontal and vertical). The hope is that one polarization
will be less severely affected when the other experiences a deep fade.
· Time Diversity

o This will transmit the desired signal in different periods of time.
o The intervals between transmissions of the same symbol should be at least the
coherence time so that different copies of the same symbol undergo
independent fading.