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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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Filter Characteristics

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 FilterCharacteristics

If an ideal low-pass filter existed, it would completely eliminate signals above the cutoff
frequency, and perfectly pass signals below the cutoff frequency. In real filters, various trade-offs
are made to get optimum performance for a given application.
Butterworth filters are termed maximally-flat-magnitude-response filters, optimized for gain
flatness in the pass-band. the attenuation is –3 dB at the cutoff frequency. Above the cutoff
frequency the attenuation is –20 dB/decade/order. The transient response of a Butterworth filter
to a pulse input shows moderate overshoot and ringing.
Bessel filters are optimized for maximally-flat time delay (or constant-group delay). This means
that they have linear phase response and excellent transient response to a pulse input. This
comes at the expense of flatness in the pass-band and rate of rolloff. The cutoff frequency is
defined as the –3-dB point.
Chebyshev filters are designed to have ripple in the pass-band, but steeper rolloff after the
cutoff frequency. Cutoff frequency is defined as the frequency at which the response falls below
the ripple band. For a given filter order, a steeper cutoff can be achieved by allowing more
pass-band ripple. The transient response of a Chebyshev filter to a pulse input shows more
overshoot and ringing than a Butterworth filter

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