Operational Amplifier Design - Coursework Example

Non-ideal Op Amps might have inputs, at the two pins, having unequal voltages; there may be current flowing out or into the two input pins. The non-ideal characteristics are responsible for circuit loading, introduced noise, and the reduced Gain and input resistance (Rin). The input offset voltage is a small voltage that is applied at the input terminals to make the output voltage zero when two inputs’ terminals are grounded.

Theory: Inverting summer amplifier 

Several signal inputs can be integrated into the inverting amplifier via the connection of individual sources with separate resistors to an Op Amp’s input; this will result in an inverted sum of all the inputs. A summing amplifier’s input combinations produce an output the reflects sum of the total inputs. Figure 1 shows a summing amplifier, a modification of an inverting amplifier; the inverting amplifier has been utilized since it can handle several or many inputs simultaneously. The summing amplifiers are practically used audio mixers and digital temperature recorders.

A prelab procedure was carried on a summing amplifier as shown in Figure 1 with the power supplies at ±10 V, choosing R1 to be 4.7 kΩ, hence VOUT= - (2 VA  + VB )  if R3 = R1 = 10kΩ. Spice was utilized in verifying both hand calculations and the circuit operation. The circuit’s plots were taken, gains compared between hand-calculations and theoretical, and the ratio of VOUT and VIN were observed using the waveform amplitudes.

The circuit was maintained as above in Figure.2, and values from the prelab were used. The dual supply was ±10 V. A 3 Pp. and 1 kHz sine was channeled at input A while a voltage of 7V from the power supply was channeled at input B. Accurate sketches of the output and input waveforms were taken: using a “DC” couple oscilloscope.

Simulation Results and Calculations

VArms=2.12 V;  VBrms=4.95V;  R1=4.7 kΩ;  R2=10 kΩ and Vout= - 7.60 V; IA=356µA; IB=449µA; and Iout=7.60pA

From the formula= = 2VA + VB it is possible to obtain the Digital to Analogue Conversion characteristics of the above Op Amp; the input VB is the Most significant Bit (the MSB), while VA is the Least Significant Bit (the LSB) since there are only 2-Bits.

The gains of individual inputs are different depending on the resistors R1 and R2. Inputs voltages to the summer configuration may add to a large value but the output of an amplifying circuit cannot surpass the rail or power supply. The Op Amp, Op-Amps incapable of pushing output voltage entirely towards the supply rails; it is evident from the voltage sums did exceed 10V; this is true since practically the output cannot reach ±10V. The output was signal of the Op Amp was inverted, Figure 2, as compared to the input signal in Figure 3.

By applying different weighting for individual voltages, the summer transforms into a digital to analogue; with the first bit having a gain of 1, then the second bit having a gain of 2. The above summing amplifier can be extended from two-bit number of input signals; since it is a two-bit digital signal that is applied at the input of the above circuit. The analog voltage appearing at the output is determined or characterized by the binary input.

The Summing Amplifier retains the advantages of an inverting amplifier, that is, it can be modified into accommodate several or multiple input signals. In addition, the circuit is linear therefore the output voltage can be found with ease via the application of the superposition principle which regards the output voltage as the weighed weighted given two input signals. The factor used in weighing is determined by using one of the input signals with the others grounded, and then analyzing the resultant circuit. Since the summer’s circuit is linear, the said analysis can be repeated for all inputs therefore easy addition of components is evident. The merit of the above approach is that it easy to recognize any effect from individual signals on the circuit’s general performance and hence the overall output can be easily extracted or obtained in each case via inspection.

Conclusion

The summer’s configuration as a converter is compromised since its performance changes with power supply and temperature variations; hence it is important to consider relevant parameters for example the offset, linearity error, gain, and monotonicity specifying over the full power supply and temperature ranges in order to have an improved or better stability performances.