Analog Circuit Design Laboratory Report - MyWeb at WIT ...

Through the use of negative feedback, the op amp can be configured so that VO is
not always in a state of saturation, but rather equal to the value in Equation 5. In the
inverting configuration the closed loop gain, given in Equation 7 as the negative ratio of
the feedback and input resistances, was proven correct as the gain -2.97 was within 2% of
the calculated value. Also for the non-inverting and voltage follower configurations, the
closed loop gains were within 1% of the calculated values. Knowing that the op amps so
closely perform according to the theoretical relationships allows for easy design of signal
conditioning circuits. To design the proper circuit, given the desired voltage gain, one
may simply choose the feedback resistor value and solve for the input resistance. For
example, to achieve a gain of -5 the designer chooses an inverting configuration and
feedback resistor of 100-kΩ. The necessary input resistance would be 20-kΩ.
The ADIFF describes the amplification amount of the detected voltage difference
between input terminals. This gain results in an output voltage of the difference amplifier
ready for application. This gain value can be controlled by the four resistors, matching
resistor pair combination at the differential amplifier inputs. For both the differential and
instrumentation amplifiers the calculated and measured values for ADIFF were within
3%.
The ACM is ideally zero since any VCM should have no amplification. This is a
tool used to help portray a real difference amplifier’s accuracy. It is responsible in
determining the CMRR, which for an ideal circumstance is infinite. Therefore, as ACM
becomes finite, the CMRR will decrease from the ideal value. For the differential
amplifier the ACM can be regulated better by using resistor values with much higher
precision. If the CMRR is too low, the differential amplifier will be ineffective since the
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