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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

NE555 SQUARE WAVE OSCILLATOR




The NE555 is connected in the astable mode and uses only three timing components (RA, RB, and Ct). A 0.01mF bypass capacitor is used on pin 5 for noise immunity. The operating restrictions of the astable mode are few. The upper frequency limit is about 100kHz for reliable operation, as a result of internal storage times. Theoretically, it has no lower frequency limit, only that which is imposed by Rt and Ct limitations. The frequency for the circuit can be calculated as:

f=   1.44____
                (RA+2RB)Ct

          =   1.44_______________
              (4.7kW+2MW)(0.0047mF)

          =   1.44________
              9.42209 x 10e-3

          =   152.8 Hz