Differential-Amp Circuits - Lab Report Example

From figure 2, the input signal was equal to the output signal (unity amplification), and in the same phase (the non-inverting amplifier); both the upper and lower Op Amps were buffer circuits. The value of output was 19.9V because the Op Amp was not ideal. V1a = V1d = 0.2V; V1b= 0V; V3a = 1.16V; V3b = -0.96V; V3d = 2.12V; Afd = 10.6; Afd % Error = 4.4%; R4 = 0.97kΩ; R5 = 0.97kΩ; Average of R5 and R4= 0.97kΩ; R6 = 9.80kΩ; R7 = 9.84kΩ; Average of R7 and R6 = 9.82kΩ For better suppression or reduction of common mode gain, there was a potentiometer connected to the LM1458C op amps.

The potentiometer maintained output voltage at OV when differential input voltage is not applied. The nulling potentiometer improved common-mode gain of small input voltage by availing even smaller input voltages, V1a=0.2V was suppressed to V3a=1.16V as seen in figure 3. A bridge was made for the generation of two different voltages. There was a difference in between measured and calculated voltages due to tolerance or level of uncertainty. The differential gain was obtained through the connection of bridge to respective inputs of the amplifier.

The output voltages at the connected bridge were nearly similar to the unconnected bridge; this is because they are connected to the Op Amp inputs that have input resistance of not less than several hundred kΩ (LM1458C has 2MΩ); V1a was equal to V1b with voltage of 0.197V which corresponded to output 21.3V. The measured differential gain was 107.878. There was minimal signal picked as observed from the oscilloscope, this was due to drifting and DC offset. This problem was caused by low-frequency DC signal; since DC is zero frequency.

We could have constructed a high pass filter with very low cutoff frequency so that the Electro Cardiogram’s signal not to degrade. So both large capacitor of more than 1µF and large resistor of more than 1MΩ should have been put in place. The instrumentation