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MOS varactors for High Frequency

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umberabbas

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I am trying to characterize MOS varactors (NMOS) to get S-parameters along with the CV-curve for this circuit. However, I am not getting a suitable result. Please have a look and point out the mistake.
MOS_vrac.pngS_para.png
 

You'd better connect NMOS substrates to GND, not to VDD. In this latter case you just generate a forward polarized pn-junction between substrate & MOS channel.
 

Also, your test-bench is wrong.Review it..
 

So I modified the test bench as shown below with the results attached. Is this the correct method for a MOS transistor to be tested as a MOS varactor?

*The inductor value is 1pH.

Here is the netlist

******************
DC Analysis `dcOp'
******************
Important parameter values:
reltol = 1e-03
abstol(V) = 1 uV
abstol(I) = 1 pA
temp = 27 C
tnom = 27 C
tempeffects = all
gmindc = 1 pS
Convergence achieved in 8 iterations.
Total time required for dc analysis `dcOp': CPU = 3 ms, elapsed = 3.39508 ms.
Time accumulated: CPU = 339.948 ms, elapsed = 2.42305 ks (40m 23.1s).
Peak resident memory used = 26.4 Mbytes.

dcOpInfo: writing operating point information to rawfile.

***********************************
DC Analysis `dc': Vtune = (-2 -> 2)
***********************************
Important parameter values:
reltol = 1e-03
abstol(V) = 1 uV
abstol(I) = 1 pA
temp = 27 C
tnom = 27 C
tempeffects = all
gmindc = 1 pS
dc: Vtune = -1.5 (12.5 %), step = 500e-03 (12.5 %)
dc: Vtune = -1 (25 %), step = 500e-03 (12.5 %)
dc: Vtune = -500e-03 (37.5 %), step = 500e-03 (12.5 %)
dc: Vtune = 0 (50 %), step = 500e-03 (12.5 %)
dc: Vtune = 500e-03 (62.5 %), step = 500e-03 (12.5 %)
dc: Vtune = 1 (75 %), step = 500e-03 (12.5 %)
dc: Vtune = 1.5 (87.5 %), step = 500e-03 (12.5 %)
dc: Vtune = 2 (100 %), step = 500e-03 (12.5 %)
Total time required for dc analysis `dc': CPU = 9.998 ms, elapsed = 10.6552 ms.
Time accumulated: CPU = 362.943 ms, elapsed = 2.42308 ks (40m 23.1s).
Peak resident memory used = 26.4 Mbytes.


****************************************************
S-Parameter Analysis `sp': freq = (40 GHz -> 80 GHz)
****************************************************
sp: freq = 41 GHz (2.5 %), step = 1 GHz (2.5 %)
sp: freq = 42 GHz (5 %), step = 1 GHz (2.5 %)
sp: freq = 43 GHz (7.5 %), step = 1 GHz (2.5 %)
sp: freq = 44 GHz (10 %), step = 1 GHz (2.5 %)
sp: freq = 45 GHz (12.5 %), step = 1 GHz (2.5 %)
sp: freq = 46 GHz (15 %), step = 1 GHz (2.5 %)
sp: freq = 47 GHz (17.5 %), step = 1 GHz (2.5 %)
sp: freq = 48 GHz (20 %), step = 1 GHz (2.5 %)
sp: freq = 49 GHz (22.5 %), step = 1 GHz (2.5 %)
sp: freq = 50 GHz (25 %), step = 1 GHz (2.5 %)
sp: freq = 51 GHz (27.5 %), step = 1 GHz (2.5 %)
sp: freq = 52 GHz (30 %), step = 1 GHz (2.5 %)
sp: freq = 53 GHz (32.5 %), step = 1 GHz (2.5 %)
sp: freq = 54 GHz (35 %), step = 1 GHz (2.5 %)
sp: freq = 55 GHz (37.5 %), step = 1 GHz (2.5 %)
sp: freq = 56 GHz (40 %), step = 1 GHz (2.5 %)
sp: freq = 57 GHz (42.5 %), step = 1 GHz (2.5 %)
sp: freq = 58 GHz (45 %), step = 1 GHz (2.5 %)
sp: freq = 59 GHz (47.5 %), step = 1 GHz (2.5 %)
sp: freq = 60 GHz (50 %), step = 1 GHz (2.5 %)
sp: freq = 61 GHz (52.5 %), step = 1 GHz (2.5 %)
sp: freq = 62 GHz (55 %), step = 1 GHz (2.5 %)
sp: freq = 63 GHz (57.5 %), step = 1 GHz (2.5 %)
sp: freq = 64 GHz (60 %), step = 1 GHz (2.5 %)
sp: freq = 65 GHz (62.5 %), step = 1 GHz (2.5 %)
sp: freq = 66 GHz (65 %), step = 1 GHz (2.5 %)
sp: freq = 67 GHz (67.5 %), step = 1 GHz (2.5 %)
sp: freq = 68 GHz (70 %), step = 1 GHz (2.5 %)
sp: freq = 69 GHz (72.5 %), step = 1 GHz (2.5 %)
sp: freq = 70 GHz (75 %), step = 1 GHz (2.5 %)
sp: freq = 71 GHz (77.5 %), step = 1 GHz (2.5 %)
sp: freq = 72 GHz (80 %), step = 1 GHz (2.5 %)
sp: freq = 73 GHz (82.5 %), step = 1 GHz (2.5 %)
sp: freq = 74 GHz (85 %), step = 1 GHz (2.5 %)
sp: freq = 75 GHz (87.5 %), step = 1 GHz (2.5 %)
sp: freq = 76 GHz (90 %), step = 1 GHz (2.5 %)
sp: freq = 77 GHz (92.5 %), step = 1 GHz (2.5 %)
sp: freq = 78 GHz (95 %), step = 1 GHz (2.5 %)
sp: freq = 79 GHz (97.5 %), step = 1 GHz (2.5 %)
sp: freq = 80 GHz (100 %), step = 1 GHz (2.5 %)
Accumulated DC solution time = 0 s.
Intrinsic sp analysis time = 0 s.
Total time required for sp analysis `sp': CPU = 3 ms, elapsed = 3.77607 ms.
Time accumulated: CPU = 365.943 ms, elapsed = 2.42308 ks (40m 23.1s).
Peak resident memory used = 26.4 Mbytes.


**************************************************
AC Analysis `ac': freq = 60 GHz, Vtune = (-2 -> 2)
**************************************************
ac: Vtune = -1.84 (4 %), step = 80e-03 (2 %)
ac: Vtune = -1.76 (6 %), step = 80e-03 (2 %)
ac: Vtune = -1.68 (8 %), step = 80e-03 (2 %)
ac: Vtune = -1.6 (10 %), step = 80e-03 (2 %)
ac: Vtune = -1.52 (12 %), step = 80e-03 (2 %)
ac: Vtune = -1.44 (14 %), step = 80e-03 (2 %)
ac: Vtune = -1.36 (16 %), step = 80e-03 (2 %)
ac: Vtune = -1.28 (18 %), step = 80e-03 (2 %)
ac: Vtune = -1.2 (20 %), step = 80e-03 (2 %)
ac: Vtune = -1.12 (22 %), step = 80e-03 (2 %)
ac: Vtune = -1.04 (24 %), step = 80e-03 (2 %)
ac: Vtune = -960e-03 (26 %), step = 80e-03 (2 %)
ac: Vtune = -880e-03 (28 %), step = 80e-03 (2 %)
ac: Vtune = -800e-03 (30 %), step = 80e-03 (2 %)
ac: Vtune = -720e-03 (32 %), step = 80e-03 (2 %)
ac: Vtune = -640e-03 (34 %), step = 80e-03 (2 %)
ac: Vtune = -560e-03 (36 %), step = 80e-03 (2 %)
ac: Vtune = -480e-03 (38 %), step = 80e-03 (2 %)
ac: Vtune = -400e-03 (40 %), step = 80e-03 (2 %)
ac: Vtune = -320e-03 (42 %), step = 80e-03 (2 %)
ac: Vtune = -240e-03 (44 %), step = 80e-03 (2 %)
ac: Vtune = -160e-03 (46 %), step = 80e-03 (2 %)
ac: Vtune = -80e-03 (48 %), step = 80e-03 (2 %)
ac: Vtune = 0 (50 %), step = 80e-03 (2 %)
ac: Vtune = 80e-03 (52 %), step = 80e-03 (2 %)
ac: Vtune = 160e-03 (54 %), step = 80e-03 (2 %)
ac: Vtune = 240e-03 (56 %), step = 80e-03 (2 %)
ac: Vtune = 320e-03 (58 %), step = 80e-03 (2 %)
ac: Vtune = 400e-03 (60 %), step = 80e-03 (2 %)
ac: Vtune = 480e-03 (62 %), step = 80e-03 (2 %)
ac: Vtune = 560e-03 (64 %), step = 80e-03 (2 %)
ac: Vtune = 640e-03 (66 %), step = 80e-03 (2 %)
ac: Vtune = 720e-03 (68 %), step = 80e-03 (2 %)
ac: Vtune = 800e-03 (70 %), step = 80e-03 (2 %)
ac: Vtune = 880e-03 (72 %), step = 80e-03 (2 %)
ac: Vtune = 960e-03 (74 %), step = 80e-03 (2 %)
ac: Vtune = 1.04 (76 %), step = 80e-03 (2 %)
ac: Vtune = 1.12 (78 %), step = 80e-03 (2 %)
ac: Vtune = 1.2 (80 %), step = 80e-03 (2 %)
ac: Vtune = 1.28 (82 %), step = 80e-03 (2 %)
ac: Vtune = 1.36 (84 %), step = 80e-03 (2 %)
ac: Vtune = 1.44 (86 %), step = 80e-03 (2 %)
ac: Vtune = 1.52 (88 %), step = 80e-03 (2 %)
ac: Vtune = 1.6 (90 %), step = 80e-03 (2 %)
ac: Vtune = 1.68 (92 %), step = 80e-03 (2 %)
ac: Vtune = 1.76 (94 %), step = 80e-03 (2 %)
ac: Vtune = 1.84 (96 %), step = 80e-03 (2 %)
ac: Vtune = 1.92 (98 %), step = 80e-03 (2 %)
ac: Vtune = 2 (100 %), step = 80e-03 (2 %)
Accumulated DC solution time = 0 s.
Intrinsic ac analysis time = 40 ms.
Total time required for ac analysis `ac': CPU = 35.994 ms, elapsed = 36.0401 ms.
Time accumulated: CPU = 401.937 ms, elapsed = 2.42312 ks (40m 23.1s).
Peak resident memory used = 26.4 Mbytes.

modelParameter: writing model parameter values to rawfile.
element: writing instance parameter values to rawfile.
outputParameter: writing output parameter values to rawfile.
designParamVals: writing netlist parameters to rawfile.
primitives: writing primitives to rawfile.
subckts: writing subcircuits to rawfile.

Spara2.pngvaractor2.png
 

umberabbas said:
So I modified the test bench as shown below with the results attached.
Is this the correct method for a MOS transistor to be tested as a MOS varactor?
Click to expand...
Needless to say, Wrong.

There is no response due to too wrong.
https://www.designers-guide.org/Forum/YaBB.pl?num=1519187411

I think you use this sets of MOS Varactors for differential VCO.

Surely consider polarity and bias.

And can you understand mode of S-parameters ?
https://www.edaboard.com/showthread.php?t=367048
https://www.edaboard.com/showthread.php?t=365152

Also surely understand following.
https://www.edaboard.com/showthread.php?t=373118
 
Last edited:

pancho_hideboo said:
Needless to say, Wrong.

There is no response due to too wrong.
https://www.designers-guide.org/Forum/YaBB.pl?num=1519187411

I think you use this sets of MOS Varactors for differential VCO.

Surely consider polarity and bias.

And can you understand mode of S-parameters ?
https://www.edaboard.com/showthread.php?t=367048
https://www.edaboard.com/showthread.php?t=365152

Also surely understand following.
https://www.edaboard.com/showthread.php?t=373118
Click to expand...

Yes it is for the differential VCO.
I need to use these transistors as varactors in my VCO design.
What changes need to be done to get certain results as mentioned. It's urgent :(
 

umberabbas said:
Yes it is for the differential VCO.
I need to use these transistors as varactors in my VCO design.
What changes need to be done to get certain results as mentioned. It's urgent :(
Click to expand...
It is impossible to make corrections since it is too wrong.
 

umberabbas said:
These MOS transistors can be tested like this or not?
https://www.edaboard.com/showthread.php?t=373118
Click to expand...
You can not understand anything at all.

First of all, polarity of MOSFETs are wrong.
Learn very basic hardly.

Use dc_feed instead of 1kohm.
Use dc_block instead of 94fF.

Evaluate Sdd, Scc, Sdc.
If you need only half value for differential drive, evaluate s11 with center node as AC ground.

Center node is a cold node for differential mode.
 

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