A few good circuits.
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The transresistance amplifier or current-voltage converter has the transfer function
So it takes an input current and outputs a voltage. Note that the input point is always at 0V, the same potential as ground. Unlike ground, however, the current flowing into the input is not lost back to the power supply. We call this point Virtual Ground or Virtual Earth. |
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A circuit that can be seen as an extension of the transresitance amplifier is the summing amplifier or mixer. It has the transfer function
You can extend this to as many inputs as you like. It has the property that it adds the inputs together but does not allow one input to affect any other. |
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The opposite of a summing amplifier is a difference amplifier or differential amplifier. It has the transfer function
For this to work properly the resistors with the same name must be well matched, that is of very nearly identical value. This circuit is usually built with 1% or better precision resistors. |
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