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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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Basic Test Equipment Needed

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Power supplies, especially switching power supplies, require the designer to viewparameters not commonly encountered in the other fields of electronics. Aside from ac and dc voltage, the designer must also look at ac and dc current measurements and waveforms, and RF spectrum analysis. Although the vision of large capital expenditures flashes through your mind when this is mentioned, the basic equipment can be obtained for under US $3000. The equipment can be classified as necessary and optional, but somewhere along the line, all the equipment will have to be used whether one buys the items or rents them.

Necessary test equipment
1. A 100MHz or higher bandwidth, time-based oscilloscope. The bandwidth is especially needed for switching power supply design. A digital oscilloscope may miss important transients on some of the key waveforms, so evaluate any digital oscilloscope carefully.
2. 10 : 1 voltage probes for the oscilloscope.
3. A dc/ac volt and ampere multimeter. A true RMS reading meter is optional.
4. An ac and/or dc current probe for the oscilloscope. Especially needed for switching power supply design. Some appropriate models are Tektronics P6021 or P6022 and A6302 or A6303, or better.
5. A bench-top power supply that can simulate the input power source. This will be a large dc power supply with voltage and current ratings in excess of what is needed. For off-line power supplies, use a variac with a current rating in excess of what is needed.
Note: Please isolate all test equipment from earth ground when testing.
Optional test equipment
1. Spectrum analyzer. This can be used to view the RFI and EMI performance of the power supply prior to submission to a regulatory agency. It would be too costly to set up a full testing laboratory, so I would recommend using an third-party testing house.
2. A true RMS wattmeter for conveniently measuring efficiency and power factor. This is needed for off-line power supplies.

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