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Mar 24th, 2019, 5:55am
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 blue111 Community Member Offline Posts: 43 Question about gyrator implementation of active inductor Mar 29th, 2018, 2:28am   I am working on a gyrator-based active inductor as described in http://www.seas.ucla.edu/brweb/papers/Conferences/LK_ISSCC15.pdfI have done a more detailed analytical analysis on Gm2 circuit block as attached with help from others.For the gyrator-based active inductor, I still have problem obtaining inductor-based behaviour, with unexpected frequency response for a series LC filter.With S11 measurement result, I am getting NEGATIVE inductance value for https://github.com/promach/frequency_trap/blob/development/test_active_inductor....Besides, I have also measured transconductance (using AC method, please see https://github.com/promach/frequency_trap/blob/development/Makefile#L19-L23) of both Gm2 circuit block and CMOS_Inverter circuit block.By using the obtained transconductance measurement results with the equation below to calculate the active inductor value, the calculation result (which is not negative) does not really match what I have for S11 measurement.Inductance = load_capacitance / [(transconductance of Gm2 circuit block) * (transconductance of CMOS inverter circuit block)]Could anyone advise ? Back to top « Last Edit: Mar 30th, 2018, 2:14am by blue111 »     IP Logged
 danmc Community Member Offline Posts: 34 Boston Re: Question about gyrator implementation of active inductor Reply #1 - Mar 30th, 2018, 7:09am   You should verify that the gm stages are in the correct operating point not only in the real circuit but especially your gm test bench.  The DC gain is high so the output of either gm stage could be railed in the gm sims.Other things that come to mind are:- bugs in the post processing (make sure an actual inductor gives the correct result)- transistor capacitances swamp out the 70 fF load- 500k degeneration gives very small gm- double check the dc operating point in the sim of the real ckt.I'll attach a sketch of what I might do for simulating the gm stages alone. Back to top IP Logged
 danmc Community Member Offline Posts: 34 Boston Re: Question about gyrator implementation of active inductor Reply #2 - Mar 30th, 2018, 7:11am   and the 2nd picture (why didn't it let me attach both?) Back to top IP Logged
 blue111 Community Member Offline Posts: 43 Re: Question about gyrator implementation of active inductor Reply #3 - Mar 30th, 2018, 8:48am   Quote:double check the dc operating point in the sim of the real ckt. The transistors are in saturation mode. Note that X1 is referring to the CMOS inverter. Back to top IP Logged
 danmc Community Member Offline Posts: 34 Boston Re: Question about gyrator implementation of active inductor Reply #4 - Apr 3rd, 2018, 12:37pm   What happens if you replace your two transconductance stages with vccs (i.e. ideal transconductance) with gms that match your simulated gms?  If that gives expected results then capacitances and maybe output resistance on your transistors is the problem.  If the vccs version matches the transistor simulation then the error is in your calculations.  I'd tend to blame capacitances and output resistance of the transistors. Back to top IP Logged
 blue111 Community Member Offline Posts: 43 Re: Question about gyrator implementation of active inductor Reply #5 - Apr 10th, 2018, 8:55am   I just found the time to continue with this circuit. Is the following vccs gyrator circuitry correct ?Adapted from https://www.edaboard.com/showthread.php?t=369072&page=2&p=1586054&viewfull=1#pos... Back to top IP Logged
 danmc Community Member Offline Posts: 34 Boston Re: Question about gyrator implementation of active inductor Reply #6 - Apr 10th, 2018, 9:45am   Apply a test voltage to IN, call it Vin.  Vout = -gm1 * Vin * (1/(CL*s)).The current you get back is Iin = gm2*Vout = gm2*(-gm1)*Vin/(CL*s)Now solve for Zin = Vin/Iin = Cl*s / (gm2*(-gm1)) and in your case this becomesZin = (0.07pF/(-20mS*-20mS)) * s  = L*sthis gives L = 175 pH.so is that what you get via simulation? Back to top IP Logged
 blue111 Community Member Offline Posts: 43 Re: Question about gyrator implementation of active inductor Reply #7 - Apr 13th, 2018, 9:06am   I have updated the test circuit accordingly.However, in order to obtain the simulated inductance, Vin/Iin , do I use DC sweep analysis on Vin in this case ? or some other analysis type ? Back to top IP Logged