Experiment EE01: Differential Amplifier.
Test of differential amplifier gain.
Test of common mode voltage rejection ratio as a function of the frequency.
Result:.
Section 1:.
The input voltage (peak-to-peak) = .
The output voltage v01 = .
The output voltage v02 = .
The outage voltage v03 is approximately zero.
Section 2:.
Input voltage (peak-to-peak) =.
Signal source frequency 100Hz 1kHz 10kHz 100kHz.
Output voltage .
Table 1: Signal source frequency against Output voltage.
Section 3:.
The output voltage v04 = .
The output voltage v05 = .
Calculations: .
The gain of the differential amplifier from the values recorded in Section 1.
= .
The Common Mode Voltage Gain in dB from the values recorded in Section 2:.
= .
Input Voltage Common mode rejection ratio in dB.
= .
Similarly,.
Signal source frequency 100Hz 1kHz 10kHz 100kHz.
Output voltage .
Common Mode Voltage Gain in dB .
Common mode rejection ratio in dB .
The graph that common mode voltage rejection ratio as a function of the frequency is attached in the appendix.
Discussion:.
The differential amplifier gain is found to be .
When the same input voltage is applied to both input terminal of an-amp, the op-amp is said to be operating in a common-mode configuration. Since the input voltage applied is common to both inputs, it is referred to as a common-mode voltage vcm. A common-mode voltage vcm can be ac, dc, or a combination of ac and ac.
Because ideally an-amp amplifies only differential input voltages, no common-mode output voltage vocm should appear at the output. However, due to imperfections within an actual op-amp, some common-mode voltage vocm will appear at the output. The amplitude of this vocm is very small and often insignificant compared common Cmode voltage vcm.
The higher the value of common-mode rejection ratio CMRR, the smaller will be the amplitudes of the output common-mode voltage vocm. Generally, the CMRR value is very large and is therefore usually specified in decibels (dB), where.