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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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Role of the Power Supply within the System and Design Program

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The three major power supply technologies that can be considered within a power supply system are:
1. Linear regulators.
2. Pulsewidth modulated (PWM) switching power supplies.
3. High efficiency resonant technology switching power supplies.
Each of these technologies excels in one or more of the system considerationsmentioned above and must be weighed against the other considerationsto determine the optimum mixture of technologies that meet the needs ofthe final product. The power supply industry has chosen to utilize each of the technologies within certain areas of product applications as detailed in thefollowing.

Linear
Linear regulators are used predominantly in ground-based equipments where
the generation of heat and low efficiency are not of major concern and also where
low cost and a short design period are desired. They are very popular as boardlevel
regulators in distributed power systems where the distributed voltage is less
than 40VDC. For off-line (plug into the wall) products, a power supply stage
ahead of the linear regulator must be provided for safety in order to produce
dielectric isolation from the ac power line. Linear regulators can only produce
output voltages lower than their input voltages and each linear regulator can
produce only one output voltage. Each linear regulator has an average efficiency
of between 35 and 50 percent. The losses are dissipated as heat.
PWM switching power supplies 
PWM switching power supplies are much more efficient and flexible in their use than linear regulators. One commonly finds them used within portable products, aircraft and automotive products, small instruments, off-line applications, and generally those applications where high efficiency and multiple output voltages are required. Their weight is much less than that of linear regulators since they require less heatsinking for the same output ratings. They do, however, cost more to produce and require more engineering
development time.
High efficiency resonant technology switching power supplies
This variation on the basic PWM switching power supply finds its place in applications where still lighter weight and smaller size are desired, and most importantly, where a reduced amount of radiated noise (interference) is desired. The common products where these power supplies are utilized are aircraft avionics, spacecraft electronics, and lightweight portable equipment and modules. The drawbacks are that this power supply technology requires the greatest amount of engineering design time and usually costs more than the other two technologies.
The trends within the industry are away from linear regulators (except for board-level regulators) towards PWM switching power supplies. Resonant and quasi-resonant switching power supplies are emerging slowly as the technology matures and their designs are made easier.

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