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I have the following Operational Transconductance Amplifier that I need to implement in LTSpice. I need to choose a value for \$R_2\$ and \$C_{inf}\$ in order to have a (theoretical)gain value \$A_v=1500\$.

What I found is that:

\$I_{C5}=I_{C6}=I_{C7}=I_{C8}=(V_{cc} - V_{be})/R_2\$;

\$I_{C1}=I_{C2} = (I_{C7} / 2 ) \cdot (\beta /(\beta+1))\$; \$I_{C4}=I_{C2}-I_{C5}\$;

\$I_{C3}=I_{C1}-I_{C3}-I_{C4}\$;

β in my case it's ~180 because I'm using an BC847A transistor. \$A=V_o/V_g = g_{m_{_{Q2}}} \cdot \beta_{q5} \cdot R_1\$ \$g_{m_{_{Q2}}}=I_{C2} / V_t\$ that it's aprox \$40\cdot I_{C2}\$.

I need to implement the following circuit in LTSpice but I don't know if my schematic is ok and what values \$C_{inf}\$ and \$R_2\$ should be.

The following constraints are imposed:

  • \$V_{CC}=10V\$
  • \$V_{CM} = 1.5V\$
  • \$R_1= 15k\Omega\$
  • \$Vg\$ is a sine wave with a frequency of 1 kHz, whose amplitude will be chosen so as to ensure minimal distortion of the output signal (i.e. \$v_0\$ should also be a sine wave);

The first picture is the schematic and the second one the LTSpice implementation.

Did I did something wrong here? enter image description here enter image description here

Math Keeps Me Busy
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bicanul123
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    How is this different from your previous question? Like I mentioned there, you need to do the small signal analysis. I suggest you take a couple of steps back. Start with a common emitter circuit and do small signal analysis on that one. I see you messing with \$\beta\$ and that tells me you're quite unfamiliar with the method you need to apply here to get to the solution. – Bimpelrekkie May 12 '20 at 11:30
  • @Bimpelrekkie And with what should I ,,mess" if it's the only info that I get?Do you have a much simpler solution for this problem? – bicanul123 May 12 '20 at 11:33
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    There is no "much simpler". To someone with experience it is all quite simple, just draw the small signal equivalent circuit and in a few steps you have an expression for the small signal gain. **Learning how to do that** is the hard part and cannot be explained "in a simple way". You're asking for shortcuts where there are none. What have **you** done to learn how to do small signal analysis? – Bimpelrekkie May 12 '20 at 11:50

1 Answers1

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I need to implement the following circuit in LTSpice but I don't know if my schematic is ok

and...

Did I did something wrong here?

enter image description here

Andy aka
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