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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 Battery Saving Disconnect Switch Circuit Diagram

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This is a Simple Battery Saving Disconnect Switch Circuit Diagram. At a predetermined level of declining terminal voltage, the circuit disconnects the battery from the load and halts potentially destructive battery discharge. Ql, a high-side, floating-source MOSFET, acts as the switch. The overall circuit draws about 500 when the switch is closed and about 8 when it`s open. 

 Battery Saving Disconnect Switch Circuit Diagram



Battery Saving Disconnect Switch Circuit Diagram

The values of ii, R2, and R3 set the upper and lower voltage thresholds, Vv and VL, according to the relationships For the circuit to start, V+ must exceed VO. The voltage detector IC1 then powers IC2, but only while V+ remains above VL. Otherwise, IC2 loses its power, removes gate drive from Ql, and turns it off. IC2 is a dual chaige-pump inverter that normally converts 5 V to + 10 V. Capacitors CI, C2, and the two associated diodes form a voltage tripler that generates a gate drive for Ql that is approximately equal to two times the battery voltage. 

With the values in the schematic, the circuit disconnects 3-cell Nicad battery from its load when V+ reaches a VL of 3.1 V. Approximately 0.5 V of hysteresis prevents the switch from turning on immediately when the circuit removes the load; V+ must first return to Vu, which is 3.6 V. The gate drive declines as the battery voltage declines, cause the ON-resistance of Ql to reach a maximum of approximately 0.1, just before V+ reaches its 3.1-V threshold. A 300-mA load current at that time will cause a 30-mV drop across the disconnect switch. The drop will be 2 to 3 mV less for higher battery voltages. Resistor R4 ensures that Ql can adequately turn off by providing a discharge path for C2.

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