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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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Direct Current Theory

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BULB & BATTERY If we take a light bulb and connect it to a battery, the bulb will light up. The lamp lights up because current flows through it.

The current leaves the battery at the negative terminal, flows through the bulb, and returns to the positive terminal of the battery *(see note 1). The electrons flow in one direction. This is known in electronics as DIRECT CURRENT flow because the electrons flow only in one direction.

The arrows in the figure show the direction that the current would flow in this circuit. As long as we can follow the current from the negative terminal of the battery throughout the entire circuit, and back to the positive terminal, we have a COMPLETE CIRCUIT PATH . It is very important to remember that current will ONLY flow if the circuit path is complete. If we were to remove the light bulb from the circuit, the circuit path would not be complete, and while voltage would still exist on the battery, no current would flow through the circuit.

In order to have any complete circuit, you are required to have at least 3 parts:
    (1) The SOURCE or SUPPLY of Voltage.
    (2) The LOAD which uses the source Voltage.
    (3) A complete path of connecting wires.

*Note 1: There are schools that teach that electric current flows from positive to negative (mostly Engineering schools) and schools that teach that electricity moves from negative to positive (mostly tech schools). Neither are truly wrong - a point which I will divulge later on in the text. The direction of travel is not as important at this point as the concept that it MUST form a complete ciruit in order to have current.