The circuit shown below is a prototype 4^th - order low-pass filter which is required to meet the specification given. However the specification is not met due to inadequate attenuation in both the pass-band and the stop-band.

You are required to first identify and correct the problem, giving theoretical explanations, and then redesign the circuit to give a unique response which will be specified by your birthdate.

i) Use ORCAD to analyse the circuit confirming that the response does not meet the required specification. In addition to the ORCAD output which should clearly show the frequencies/gains where the response is not met you must also provide a brief report to confirm your analysis.

ii) Use ORCAD to determine which components need to be changed to enable the specification to be met. You are advised to systematically change the circuit components and then comment on the effects of these changes on the circuit response. Note that theoretical calculations are not required here.

iii) Give a theoretical explanation, based on a model for the operational amplifiers and the behaviour of capacitors at high frequencies, why the changes made in part (ii) are successful. (There are many texts on PSPICE which contain appropriate operational amplifier models used by ORCAD. Do not forget to include the reference for the model you use).