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Given Parameters: 1KHz 10mV sine wave as excitation(Vin) Circuit as given in the question

Specifications to be matched:

Input Resistance(Rin) = 18 KΩ,

Current gain = 33 dB,

3 dB Bandwidth = 425 KHz

We are allowed to vary R2,R3( refer 2nd figure below) and Capacitor values to meet the specifications.

My attempt: I started with Rin and to match it, I varied R2 values using LTSPICE and got it to be 31.73K enter image description here Now the problem is when I try to meet ideal current gain or 3dB bandwidth specifications by fixing this R2=(31.73K) and by varying R3 or the capacitors, my Rin is bound to deviate from given specification I just matched, so I'm not really sure as to how to go forward and match other specification after the first one.

Fresh attempt: I took a different approach and only varied R2 and kept R3 fixed. I varied R2 values to match current gain of 33dB and got 46.22Kohm. and when I tried to match Rin, I got 29.19Kohm but then I realized on changing the C2 value to say 706n the gap between the two R2 values gets bridged and I get 35.209Kohm for matching current gain and 32.92Kohm for matching Rin and 3dB bandwidth isn't affected much and is nearly 416kHz but I do not have a concrete way to vary C2 ( except randomly changing it) whereby I can simultaneously check which two R2 values gives required current gain and Rin and actually bridge the gap between the two.

EDIT: Model to be used- enter image description here As for the Voltage gain spec, we aren't required to meet any so we just have go as much closer to only the three given specs.

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    \$\begingroup\$ I like how the 1st picture has two completely useless crossing dots at the collector, but none at the base. \$\endgroup\$ – a concerned citizen Mar 7 at 22:44
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Current gain of 33 dB means 44 and current GBW becomes ~15 MHz which is easily met.

But Rin depends on hFE * (Re+Rbe) which when bypassed for AC just becomes hFE * Rbe where Rbe = 26/Ic (mA) so that won't work.

No voltage gain spec? No Attenuation spec? your emitter cap is shorting the AC input at some frequency.

Output impedance is Rsource / hFE and 1mV is small and the current gain = hFE as long as load AC current does not exceed DC emitter bias current.

Try again.

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  • \$\begingroup\$ Thanks! Please have a look at the edits and the fresh attempt as well. \$\endgroup\$ – Manan01 Mar 8 at 8:55
  • \$\begingroup\$ No. You have design that not only can be unstable with any circuit inductance, this is how not to design a signal amplifier. Why do you think this is a linear amplifier for the signal? \$\endgroup\$ – Tony Stewart EE75 Mar 8 at 13:46

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