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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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Digital Composite op Amplifier Circuit Diagram

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Build a Digital Composite op Amplifier Circuit Diagram. In the most general sense of the word, any additional circuitry at either the input or the output of an amplifies. A composite configuration greatly reduces de errors without compromising the high-speed, wide band characteristics of HA-2539. The HA-2540 could also be used, but with slightly lower speeds and bandwidth response. 




The HA-2539 amplifies signals above 40 kHz which are fed forward via C2; R2 and R5 set the voltage gain at -10. The slew rate of this circuit was measured at 350 V /p.s. Settling time to a 0.1 % level for a 10-V output step is under 150 ns and the gain bandwidth product is 300 MHz. The HA-5170 amplifies signals below 40kHz, as set by C1 and R1, and controls the de input characteristics such as offset voltage, drift, and bias currents of the composite amplifier. 

Therefore, it has an offset voltage ofl00 p.V, drift of 2 p.V/°C, and bias currents in the 20-pA range. The offset voltage can be externally nulled by connecting a 20-KO pot to pins 1 and 5; with the wiper tied to the negative supply. The de gains of the HA-5170 and HA-2539 are cascaded; this means that the de gain of the composite amplifier is well over 160 dB. The excellent ac and de performance of this composite amplifier is complemented by its low noise performance, 0.5-p. V rms from 0.1 Hz to 100Hz. It is very useful in high-speed data acquisition systems.

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