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17th September 2019, 16:29 #1
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deviding Y value by X values in Cadence Virtuoso calculator
Hello,
I need to calcultae the input capacitance of the amplifier from
Cin_diff=imag(Yin_diff)/(2*pi*freq)
the frequency is the sweeping parameter comes by running the AC simulation in the xaxsis. How can I put in the formula of Cin ?
Thank you

17th September 2019, 17:15 #2
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Re: deviding Y value by X values in Cadence Virtuoso calculator
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17th September 2019, 18:23 #3
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Re: deviding Y value by X values in Cadence Virtuoso calculator
Dear Pancho,
Thank you for your help,
I used the xval function as shown below
where i7 represent imag_Y which is measured at d from balun for CMOS fully differential amplifier.
the differential input capacitance is given below
I wondering why input capacitance is decreasing at a higher frequency, I was expecting it to increase as the parasitics starts to appear at high frequency
Thank you

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17th September 2019, 18:28 #4
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Re: deviding Y value by X values in Cadence Virtuoso calculator
Simply your equation is wrong.
You have to apply imag() for numerator.
Generally Capacitance is nearly constant over frequency.Last edited by pancho_hideboo; 17th September 2019 at 18:43.
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17th September 2019, 18:49 #5
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Re: deviding Y value by X values in Cadence Virtuoso calculator

17th September 2019, 19:00 #6

18th September 2019, 09:01 #7
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Re: deviding Y value by X values in Cadence Virtuoso calculator
Dear Pancho,
it will be nice and very kind of you if you could then tell me the right procedure,
do you mean I first plot the current (which represent the admittance) in Magnitude, then I send this value to calculator and use the function "imag" ?
Thank you very much

18th September 2019, 11:30 #8
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Re: deviding Y value by X values in Cadence Virtuoso calculator
Surely see legend of ViVA.
imag() is not applied.
Simply apply imag() in numerator.
If you plot complex value without applying any function, Cadence ViVA plots absolute value.Last edited by pancho_hideboo; 18th September 2019 at 11:37.
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18th September 2019, 13:03 #9
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Re: deviding Y value by X values in Cadence Virtuoso calculator
Dear Pancho,
Thank you again for your kind answer
I am applying the "imag" function to the magnitude signal and the result are the same, it shows both have the exact value as you see from the third image (result signal is the one with image fucntion applied)
below is the admitance in magnitude
here I sent the signal to calculator
here is the result after calculator
Thank you very much

19th September 2019, 14:40 #10
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Re: deviding Y value by X values in Cadence Virtuoso calculator
See attached figure.
Rather I suspect your test bench, since you still can not understand linear circut basics such as differentail mode, common mode, ideal transfomer and etc. at all.
https://www.edaboard.com/showthread.php?386628
Show me netlist regarding signal sources, loads, balun and analysis statements.
"test_Junus2012.scs"Code:// Generated for: spectre // Generated on: Sep 19 09:28:54 2019 // Design library name: My_RFDE_Test // Design cell name: test_Junus2012 // Design view name: schematic simulator lang=spectre global 0 // Library name: My_RFDE_Test // Cell name: test_Junus2012 // View name: schematic V0 (net2 0) vsource dc=1 mag=1 type=dc IPRB0 (net2 net1) iprobe R0 (net1 0) resistor r=10 C0 (net1 0) capacitor c=100p simulatorOptions options psfversion="1.1.0" reltol=1e3 vabstol=1e6 \ iabstol=1e12 temp=25.0 tnom=25.0 scalem=1.0 scale=1.0 gmin=1e12 \ rforce=1 maxnotes=5 maxwarns=5 digits=5 cols=80 pivrel=1e3 \ sensfile="../psf/sens.output" checklimitdest=psf ac ac start=10M stop=1G dec=50 annotate=status save IPRB0:in saveOptions options save=selected
Last edited by pancho_hideboo; 19th September 2019 at 14:53.
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23rd September 2019, 16:53 #11
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Re: deviding Y value by X values in Cadence Virtuoso calculator
Dear Pancho thank you for your reply and sorry to make you upset,
here is the netlist
Code:// Library name: analogLib // Cell name: ideal_balun // View name: schematic subckt ideal_balun d c p n K0 (d 0 p c) transformer n1=2 K1 (d 0 c n) transformer n1=2 ends ideal_balun // End of subcircuit definition. // Library name: sen_In_Amp_fully_11_layout2 // Cell name: In_Amp_fully_11_layout_AC3_test // View name: schematic V3 (net4 0) vsource dc=1.65 type=dc V4 (net17 0) vsource dc=VCM type=dc V1 (net018 0) vsource dc=1.65 type=dc V0 (vdd! 0) vsource dc=3.3 type=dc PD_S (PD 0) vsource dc=PD type=dc XPD_S (XPD 0) vsource dc=XPD type=dc R5 (Vout_diff 0) resistor r=200k R1 (Vout\+ net33) resistor r=100 R2 (net33 net32) resistor r=100k R3 (net32 Vout\) resistor r=100 C1 (Vout_diff 0) capacitor c=2.5p V11 (VID 0) vsource mag=1 type=sine ampl=1.6 freq=1K I6 (0 PD net17 vdd! XPD net28 Vin\+ net4 Vout\+ Vout\ net4 vin\) \ In_Amp_fully2 I10 (vdd! net28) isource dc=Ibias type=dc I7 (VID net018 Vin\+ vin\) ideal_balun I19 (Vout_diff VOC Vout\+ Vout\) ideal_balun simulatorOptions options reltol=100e6 vabstol=1e6 iabstol=1e12 temp=27 \ tnom=27 homotopy=all limit=delta scalem=1.0 scale=1.0 \ compatible=spice2 gmin=1e12 rforce=1 maxnotes=5 maxwarns=5 digits=5 \ cols=80 pivrel=1e3 sensfile="../psf/sens.output" checklimitdest=psf dcOp dc write="spectre.dc" maxiters=150 maxsteps=10000 annotate=status dcOpInfo info what=oppoint where=rawfile ac ac start=1 stop=100M dec=100 annotate=status designParamVals info what=parameters where=rawfile primitives info what=primitives where=rawfile subckts info what=subckts where=rawfile save I7:1 saveOptions options save=allpub
The circuit about is fully differential instrumentatin amplifier, it employes the same concept of fully differential amplifire where I want to test Cin
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