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High CMRR Instrumentation Amplifier (Schematic and Layout) design for biomedical applications

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

Charge Pool Power supply Circuit Diagram

It is usually desirable to have the remote transmitter of a 4 to 20 mA current loop system powered directly from the transmission line. In some cases, this is not possible because of the high-power requirements set by the remote sensor/transmitter system. In these cases, an alternative to the separate power supply is still possible. 

If the remote transmitter can be operated in a pulsed mode where it is active only long enough to perform its function, then a charge pool power supply can still allow the transmitter to be powered directly by the current loop. In this circuit, constant current II is supplied to the charge pool capacitor, CP, ~! the HA-5141 (where II ~ 3 mA). 

The voltage VI continues to rise until the output of the HA-5141 approaches + V, or the optional voltage limiting provided by Z2. The LM2931 voltage regulator supplies the transmitter with a stable + 5 V supply from the charge collected by CP. Available power supply current is determined by the duration, allowable voltage droop on CP, and required repetition rate.

Charge Pool Power supply Circuit Diagram



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