Wednesday, December 24, 2008

ANALOGY FOR DIVIDED FEEDBACK

We know that the voltage gain of a noninverting amplifier configuration can never be less than unity (1).

The "output" point will move twice as far as the "input" point, and in the same direction. The output voltage will equal twice the input, with the same polarity. Applying a negative input voltage is analogous to moving downward from its level "zero" position, resulting in an amplified output displacement that is also negative.
If we alter the resistor ratio R2/R1, we change the gain of the op-amp circuit. This means moving the input point, which similarly changes the displacement "gain" of the circuit. Now, any input signal will become amplified by a factor of four instead of by a factor of two.
With the inverting configuration, the ground point of the feedback voltage divider is the op-amp's inverting input. With equal-value resistors, the output voltage will be equal in magnitude to the input voltage, but of the opposite polarity. A positive input results in a negative output. Changing the resistor ratio R2/R1 changes the gain of the amplifier circuit.
With the inverting amplifier configuration, gains of less than 1 are possible,. Reversing R2 and R1 values the output displacement will be one-half the input displacement.

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