A basic common-source potential divider JFET circuit is given with existing values, and with me calculating them with the help of another user in this forum:

\(V_{DD} = 20V\) (Power Supply)

\(I_{DSS} = 10mA\)

\(I_{DQ} = 3mA\)

\(V_G = 1.728V\)

\(V_{GSQ} = -1.357V\)

\(V_{GS(OFF)} = -3V\)

\(V_{DS} = 7V\)

\(g_m = 3.51mS\)

\(R_S = 1028\Omega\)

\(R_D = 3305\Omega\)

\(R_1 = 1585450\Omega\)

\(R_2 = 150k\Omega\)

\(R_L = 10k\Omega\)

\(r_d = \infty\) (negligible)

My objective now is to find the bypass/coupling capacitance values (C1/Cs/C2) and the signal (internal) resistance using a low-frequency small signal analysis so that I can find the cutoff frequencies:\(f_{L_{C_{i}}}, f_{L_{C_{o}}}, f_{L_{C_{s}}}\)

\(f_{L_{C_{i}}}\) = Lower cut-off frequency at capacitor Ci = \(\frac{1}{2\pi(R_{sig}+(R_1||R_2))C_i}\)

\(f_{L_{C_{o}}}\) = Lower cut-off frequency at capacitor Co = \(\frac{1}{2\pi(R_D+R_L)C_o}\)

\(f_{L_{C_{s}}}\) = Lower cut-off frequency at capacitor Cs = \(\frac{1}{2\pi(R_{eq})C_s}\), where \(R_{eq}\) = \(R_S || \frac{1}{g_m}\)

I can find the equivalent resistance from the bypass capacitor Cs at the source resistance Rs using the above formula, but then what to do next? I do not have the values of Rsig (signal resistance) and the capacitance values. The solutions I have tried are:

1. I attempted to use this online resource in finding Rsig. Though, my assignment question did not provide the value of Vsig so I am unable to use the equations provided in that resource.

2. I am unable to use the internal/stray capacitance that become available at high frequency, because I am supposed to solve this at low frequency.

3. Although I can find the voltage gain at midrange frequency, I fail to see how it can help me in finding the aforementioned values unless I am missing out on something.

Pointing me in the right direction would be very helpful. Thanks!

Mod edit: added image from link.

\(V_{DD} = 20V\) (Power Supply)

\(I_{DSS} = 10mA\)

\(I_{DQ} = 3mA\)

\(V_G = 1.728V\)

\(V_{GSQ} = -1.357V\)

\(V_{GS(OFF)} = -3V\)

\(V_{DS} = 7V\)

\(g_m = 3.51mS\)

\(R_S = 1028\Omega\)

\(R_D = 3305\Omega\)

\(R_1 = 1585450\Omega\)

\(R_2 = 150k\Omega\)

\(R_L = 10k\Omega\)

\(r_d = \infty\) (negligible)

My objective now is to find the bypass/coupling capacitance values (C1/Cs/C2) and the signal (internal) resistance using a low-frequency small signal analysis so that I can find the cutoff frequencies:\(f_{L_{C_{i}}}, f_{L_{C_{o}}}, f_{L_{C_{s}}}\)

\(f_{L_{C_{i}}}\) = Lower cut-off frequency at capacitor Ci = \(\frac{1}{2\pi(R_{sig}+(R_1||R_2))C_i}\)

\(f_{L_{C_{o}}}\) = Lower cut-off frequency at capacitor Co = \(\frac{1}{2\pi(R_D+R_L)C_o}\)

\(f_{L_{C_{s}}}\) = Lower cut-off frequency at capacitor Cs = \(\frac{1}{2\pi(R_{eq})C_s}\), where \(R_{eq}\) = \(R_S || \frac{1}{g_m}\)

I can find the equivalent resistance from the bypass capacitor Cs at the source resistance Rs using the above formula, but then what to do next? I do not have the values of Rsig (signal resistance) and the capacitance values. The solutions I have tried are:

1. I attempted to use this online resource in finding Rsig. Though, my assignment question did not provide the value of Vsig so I am unable to use the equations provided in that resource.

2. I am unable to use the internal/stray capacitance that become available at high frequency, because I am supposed to solve this at low frequency.

3. Although I can find the voltage gain at midrange frequency, I fail to see how it can help me in finding the aforementioned values unless I am missing out on something.

Pointing me in the right direction would be very helpful. Thanks!

Mod edit: added image from link.

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