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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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Build a 5V Supply Circuit Diagram

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This 5V Supply Circuit Diagram protects microprocessor systems from `brownouts` without the expense of an uninterpretable power supply. Designed around a small 9-V nickel cadmium battery the circuit continues to provide a constant 5-V output during brownouts of up to a few seconds. Load currents of up to 500 mA may be drawn using the components shown. 

With this mains-derived supply present, D5 is forward biased so that the stabilized supply powers the 5-V regulator and hence the circuitry to be protected. FET Tj is held on by Dl, its drain current being provided from the dc supply via Rb and D2. Diode D3 is reverse-biased so that T2 is off, and the battery is isolated from D6. RCH and D4 serve to trickle charge the battery with approximately 1.2 mA. 

 5V Supply Circuit Diagram

5V Supply Circuit Diagram


When the 12-V supply is removed, Rl and Cl initially keep Tl switched on. D3 is now forward biased, so that Tl drain current is drawn via Rb, D3 and T2 from the battery. This switches T2 on, allowing the load circuitry to draw current from the battery via D6 and the 5-V regulator. After a few seconds Cl has discharged (via Rl) such that Vgs falls below the threshold value for the FET, and Tl switches off. There is then no path for T2 base current, so that it also switches off, isolating the battery.

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