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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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Simple Switch-Mode Voltage Regulator Circuit Diagram

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This is a Simple Switch-Mode Voltage Regulator Circuit Diagram. This Simple Switch-Mode Voltage Regulator Circuit Diagram power supplies offer the benefit of a much greater efficiency than obtainable with a traditional power supply. The Simple Switch-Mode Voltage Regulator Circuit Diagram presented here has an efficiency of around 85%. An input voltage of 12 to 16 Vdc is converted into a direct voltage of exactly 5 V. 


Simple Switch-Mode Voltage Regulator Circuit Diagram



The use of a MAX638CPA enables the design and construction of the regulator to be kept fairly simple: only nine additional components are needed to complete the circuit. Resistors RI and R2 are used to indicate when the battery voltage becomes low: as soon as the voltage on pin 3 becomes lower than 1.3 V, D1 lights. With values as shown for the potential divider, this corresponds to the supply voltage getting lower than about 6.5 V. 

The output of the IC is shunted by a simple LC filter formed by LI, C3 and D2. The oscillator on board the IC generates a clock frequency of around 65 kHz and drives the output transistor via two NOR gates. The built-in error detector, the `battery low` indicator or the voltage comparator can block the clock frequency, which causes the transistor to switch off. The IC compares the output voltage of 5 V with a built-in reference (FET). Depending on the load, the FET will be switched on for longer or shorter periods. The maximum current through the FET is 375 mA, which corresponds with a maximum output current of 80 mA.

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