comparing CS and Cascode frequency response

Matteo · 2007-05-02T22:43:59+00:00

hi all,I calculated the frequency response of the CS and Cascode amplifiers using the time constants method. Here they are:CSf = ( 2*PI*( Rs*Cgs + Rs*Cgs*(1+Av) + Rd*(Cdb+Cl)) )-1Cascodef = ( 2*PI*(Rs*Cgs1 + Cds1*2*Rs + Rd*(Cgd2+Cdb2*Cl) + 1/gm2*(Cdb1+Cgs2) )-1where:Rs = resistance of the imput signalRd = resistance under VddCl = load capacity Vdd | Rd |----------o Vout --- |Vcost--|| = --> | | ground | --- ----|| | --> Rs | | | Vin ground | groundI calculated f usingRs = 50ohmRd = 600ohmW = 592 micronand I obtainedCS => f = 1.98EE+08Cascode => 2.08EE+08and I think that's a really little difference! where did I make the mistake?thank you very much!

May 02, 2007 21 Replies

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Matteo 19 years ago

gosh ..the right expression is:

f = ( 2*PI*(Rs*Cgs1 + Cgd1*2*Rs + Rd*(Cgd2+Cdb2+Cl) + 1/gm2*(Cdb1+Cgs2) )-1

and with the values f = 2.08EE+08 Hz.. very similar to the CS's one

you sad that you got a corner frequency of 315 MHz for the CS amplifier, and a corner frequency of 984 MHz for the cascode.

did you get these values using the simulator? they are really very different from the values obtained from manual calculations...

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Rodger Rosenbaum 19 years ago

Yes.

Yes, especially the cascode.

If you'll email me at r_o_d_g_e_r_r_o_s AT yahoo.com (take out the underlines in the name), I'll send you the results of the simulations.

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