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Difference amplifier
The purpose of this section is to introduce precision amplifiers and to learn
to distinguish differential and common mode signals.
Ref: Simpson, Ch. 9-10, esp. Sec. 9.8.7, 10.4; Faissler, Ch. 31 (review); Malmstadt et al., Ch. 8.1.
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- Calculate the average gain of the amplifier. In this measurement, which
components determine the gain of the amplifier? How does the measured value
compare with the theoretical one?
- Connect to a constant +1V source and repeat the above two steps.
- Connect both and to the same variable voltage source;
measure for several values of between V and V.
- Plot vs. and determine the value of the common mode
gain from the plot.
- Interpret your data in terms of the imbalance of the resistance ratios of the
two pairs of resistors determining the gain, for the inverting and for the
non-inverting input. Which pair has the higher gain and by how much?
How could this common mode gain be reduced?
- Calculate the common-mode rejection ratio (CMRR) for your difference
amplifier. Calculate the maximum common-mode signal the amplifier can accept
if a 100 mV signal is to be amplified with an error of less than 0.1%.
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Up: Advanced op-amp designs
Previous: Op-amp differentiator
For info, write to: physics@brocku.ca
Last revised: 2007-01-05