THD from Spice simluation

[sam244]

Hi Elvee,


Its very glad to hear from you......Our output expression is Iout=Id(M12)-Id(M13)....so how to see the thd for this output.....because .four does not support this expression....

[jcx]

a few things

this is a multiplier circuit so the appropriate freq for the .four is the fundamental of the output - which is 2x the input

.tran should have step size Tstep and max step dTmax much smaller than the period of anything going on in the circuit to give good resolution and "realistic" distortion # - I changed them to 10nS

an Arbitrary Behavioral source can be used for waveform arithmetic

after you Simulate you can rt click in the plot area
add trace - shows available vars
or even fft - shows the very low 1 MHz "leakage" in the output

modded lines:

.Tran 10ns 100us 0ms 10ns
BI1 0 0 I=(Id(M12)-Id(M13))
.Four 2Meghz I(BI1)

Error Log:

Circuit: ** Gilbert Cell **

Ignoring BSIM parameter XL
Ignoring BSIM parameter XW
Ignoring BSIM parameter XL
Ignoring BSIM parameter XW
Warning: Pd = 0 is less than W.
Warning: Ps = 0 is less than W.
Warning: Pd = 0 is less than W.
Warning: Ps = 0 is less than W.
Warning: Pd = 0 is less than W.
Warning: Ps = 0 is less than W.
.step a=1
Direct Newton iteration for .op point succeeded.
Fourier components of I(bi1)
DC component:-0.00022244

Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 2.000e+06 5.348e-05 1.000e+00 58.06° 0.00°
2 4.000e+06 1.002e-06 1.873e-02 50.24° -7.81°
3 6.000e+06 2.637e-07 4.930e-03 -81.36° -139.42°
4 8.000e+06 1.029e-07 1.924e-03 83.78° 25.72°
5 1.000e+07 8.911e-08 1.666e-03 153.70° 95.64°
6 1.200e+07 1.154e-07 2.158e-03 -57.77° -115.82°
7 1.400e+07 1.058e-07 1.979e-03 82.26° 24.20°
8 1.600e+07 3.886e-08 7.267e-04 133.01° 74.95°
9 1.800e+07 4.831e-08 9.033e-04 -116.79° -174.85°
Total Harmonic Distortion: 1.979001%


.step a=2
Fourier components of I(bi1)
DC component:-0.000237197

Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 2.000e+06 6.595e-05 1.000e+00 61.12° 0.00°
2 4.000e+06 2.791e-06 4.232e-02 58.87° -2.25°
3 6.000e+06 6.872e-07 1.042e-02 -136.65° -197.77°
4 8.000e+06 3.385e-07 5.132e-03 -55.22° -116.35°
5 1.000e+07 7.404e-08 1.123e-03 4.35° -56.78°
6 1.200e+07 2.470e-07 3.745e-03 118.76° 57.64°
7 1.400e+07 7.445e-08 1.129e-03 -128.27° -189.39°
8 1.600e+07 9.548e-08 1.448e-03 -95.52° -156.64°
9 1.800e+07 3.556e-08 5.392e-04 -0.71° -61.83°
Total Harmonic Distortion: 4.409884%

.step a=3
Fourier components of I(bi1)
DC component:-0.000260279

Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 2.000e+06 8.517e-05 1.000e+00 63.18° 0.00°
2 4.000e+06 5.828e-06 6.842e-02 56.42° -6.76°
3 6.000e+06 9.696e-07 1.138e-02 -158.36° -221.55°
4 8.000e+06 4.044e-07 4.748e-03 -118.82° -182.01°
5 1.000e+07 3.679e-07 4.320e-03 -49.24° -112.43°
6 1.200e+07 6.515e-08 7.650e-04 -66.15° -129.33°
7 1.400e+07 1.986e-07 2.331e-03 92.63° 29.45°
8 1.600e+07 1.101e-07 1.293e-03 127.05° 63.86°
9 1.800e+07 6.230e-08 7.315e-04 -144.66° -207.85°
Total Harmonic Distortion: 6.972069%

.step a=4
Fourier components of I(bi1)
DC component:-0.00029115

Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 2.000e+06 1.106e-04 1.000e+00 63.98° 0.00°
2 4.000e+06 1.020e-05 9.228e-02 56.00° -7.98°
3 6.000e+06 1.204e-06 1.089e-02 -176.98° -240.97°
4 8.000e+06 7.661e-07 6.928e-03 -146.62° -210.60°
5 1.000e+07 2.604e-07 2.355e-03 -70.50° -134.48°
6 1.200e+07 3.601e-07 3.256e-03 -60.43° -124.41°
7 1.400e+07 5.367e-08 4.853e-04 -4.16° -68.15°
8 1.600e+07 1.433e-07 1.296e-03 81.93° 17.95°
9 1.800e+07 1.311e-07 1.186e-03 112.34° 48.36°
Total Harmonic Distortion: 9.327891%


Date: Thu Mar 19 16:45:49 2009
Total elapsed time: 17.004 seconds.

tnom = 27
temp = 27
method = modified trap
totiter = 37041
traniter = 37032
tranpoints = 13916
accept = 12375
rejected = 1541
matrix size = 28
fillins = 8
solver = Normal
Matrix Compiler1: 1.72 KB object code size 2.2/1.8/[1.4]
Matrix Compiler2: off [1.9]/2.0/2.1

[sam244]

Hi JcX,

Thanks for all that useful points...I am not aware of these things....One more point.....after simulating with these conditions i am getting THD of around 12% ......so i want to know.....what are the limits on the input voltage and frequency.....for simulating THD......and also what are the ways to reduce it......??I am attaching the IEEE paper which i am going to simulate....hope to see ur reply soon...

[sam244]

Hi all,


I want to perform pole zero analysis of my circuit....which is having two voltage inputs(differential) and current output(single ended)...in LTSpice...what are the commands.. please help.....


Thanks in advance...

[d1983]

So, I have the THD simulations working for a frequency sweep and I have two questions:

1. Is it possible to add in a spice operative so that the transient plot doesn't graph? It's nice to see the multiple sine waves float across the screen, but I think it'd be faster without them.....

2. Is it possible to add a spice operative for windowing functions? I think that the fourier would be more accurate if there was a way to window the transient graph. I guess I could always increase the number of points of the FFT, or only do analysis on frequencies that would have harmonics that lie in a complete cycle within the transient, but it'd be nice to window it so I didn't have to worry as much.

Thanks all. This is a very clever group of people and I learn a lot from here.

[tiefbassuebertr]

in this case this thread could be of interest:
Transistor modeling - how do I generate P-Spice Parameter ?

[keantoken]

We have a wiki for this...

Common Issues Encountered By New Users - diyAudio

- keantoken