Operational Amplifier Fundamentals Unit 1 – The Operational Amplifier
Closed-loop mode operation is established by a resistor connected between the op amp output
and inverting input terminals. The resistor allows a portion of the output voltage to be fed back
as negative, or degenerative, feedback.
Negative, or degenerative, feedback reduces the gain (from the open-loop value) of an op amp.
Although circuit gain is reduced, negative feedback improves circuit stability by preventing
unwanted oscillation and distortion.
NEW TERMS AND WORDS
operational amplifier (op amp) - a linear device used to generate an output voltage proportional
to the differential input voltage.
integrated circuit (IC) - an interconnected array of components (resistors, transistors, etc.)
contained on a single chip of a host substrate material.
Inverting (-) - the input terminal of an op amp which reverses the polarity of the applied input
voltage.
noninverting (+) - the input terminal of an op amp which does not reverse the polarity of the
applied input voltage.
open loop mode - an op amp configuration without external feedback between output
and input.
Closed-loop mode - an op amp configuration that feeds back a portion of the output voltage to
the inverting input.
input bias current - the current entering into both inputs of an op amp.
output-offset voltage - the output error voltage present when the input voltage is 0 Vdc.
drift - the change in offset current
and offset voltage generated
by a change in temperature.
input-offset current - the difference between the two input bias currents when the output
voltage is zero.
input-offset voltage - the voltage that must be applied to the two inputs of an op amp in order to
produce an output voltage of zero.
offset nulling - the process of balancing an op amp and adjusting its output voltage to zero.