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This is a high gain, simple Bjt replica of an OP AMP. It also closely resembles a long tailed pair differential amp.
The simplest form of this circuit (having lower gain) would be taking the output from the ORANGE Trace, and removing the far right resistor and PNP & NPN transistor. No current limiting resistors are necessary on the inputs, as long as the emitter resistor isn’t too low of a value. Adjusting this resistance value will control the current consumption, including the input current, which can go very low.
THE OUTPUTS:
1. High gain: RED Trace
2. Medium gain: ORANGE Trace
The INPUTS:
1. Positive/ non-inverting (+) : GREEN Trace
2. Negative/ inverting (-) : BLUE Trace
The outputs will go high any time the left input is higher than the right. So the left input is the non-inverting (Positive) input, while the right is the inverting (Negative) input.
*** Notable differences from an OP AMP: ***
1. The output cannot sink as much current as it can source. This is because the output pulls LOW through a single pull-down resistor, but pulls HIGH through the PNP transistor.
2. The output does not go negative or require a split power supply like some other OP Amps. The floor is a minimum of 0v.
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