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  1. P

    Explanation of the LOD effect

    length of diffusion lod Are you referring to Length of Diffusion effect? Well, it's a phenomenon that is causing some detrimental effects on some circuit performance in deep sub-micron process (0.13um and below). I am not a process guy, so I may not be able to explain the exact reason behind...
  2. P

    THD of Pulse Width Modulated Sine Wave in Spectre

    pulse-width modulated sine wave Hi, I read it from "The Designer's Guide to Spice and Spectre", that we are able to find the THD of a pulse-width modulated sine wave using the Fourier Integral method by Spectre. The book also mentioned that Fourier integral is not subjected to aliasing. Now...
  3. P

    question about simulation

    Well, not true. If it's an ideal THD, you should get -infinity theorectically. Try using a smaller time step to get the THD of an ideal sine wave. You will notice that the THD improves as the time step gets smaller. Try and see.
  4. P

    Matlab Script for ADC SNR Post-Processing

    adc snr matlab Hi, I have some question regarding the script I got. Part of it is as follows: . . . % Create the minimum, 4-term Blackman-Harris window for FFT pwr_win=0; for i=1:Nt %where Nt is the no. of FFT bins...
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    Stability of sample and hold circuit

    Hi, I was wondering if it is neccessary to do a stability check on the circuit in hold mode? My thinking is that since there is a holding capacitor in the feedback loop, the loop is broken (from dc point of view). And also the capacitor is there to hold the charges and there should not be any...
  6. P

    How is the crystal drive level determined?

    I am currently designing a crystal oscillator. From crystal datasheet, there is usually a specification known as drive level. Is the drive level of the crystal determined by the crystal or is it determined by the oscillator circuit design? Thank you.
  7. P

    What's wrong with this opa?

    Dear wjxcom, Could you please attach your ac and tran simulation result as well. We can't do anything without looking at the plot. Thanks!
  8. P

    Phase margin problem as circuit is unstable at 100MHz

    Re: Phase margin problem Could you please attach the complete Bode plot? I need to take a look at the gain plot as well.
  9. P

    Fast start-up crystal oscillator know-how

    Dear All, I am a new to xtal oscillator design and I hope I can find some useful tips here regarding the start-up transient simulation. I found this website quite useful: https://members.spsdialup.com/mts@spsdialup.com/spice/xtal/clapp.htm. However, when I tried to use the method in my...
  10. P

    Nature of roots of a cubic equation

    Thanks, I see your point. By the way, do you happen to know how to determine whether the complex poles reside in the LHP or RHP by looking at the relationship among the coefficients of the cubic equation?
  11. P

    Nature of roots of a cubic equation

    I have derived a transfer function containing 3 poles. All the coefficients are positive but from matlab analysis, there is one LHP real pole and a pair of RHP complex poles. Previously, I have a misconception that a cubic equation having all +ve coeff will yield all poles in the LHP. Could...
  12. P

    Loop stability question?

    Try to find a common point between the two loops, if such a point exists. Then break the loops at that particular point to analyze the loop stability. If such a analysis is too difficult, run a transient analysis. Hopefully you won't see ringings in the waveform.
  13. P

    problems about chopper amplifier analysis with pss+pnoise

    Re: problems about chopper amplifier analysis with pss+pnois Just curious about the pnoise plot. From papers I read about chopper stabilization method, the 1/f noise of the PSD of chopper amplifier should be shifted to odd harmonics of chopping frequency. But in the PSD plot, I could still see...
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    Help me decide whether I need to add another buffer to a LDO regulator

    Re: LDO question The ability to suppress the power supply noise depends on the bandwidth of the loop gain. Once the loop gain starts to drop, the loop can no longer rejects power supply noise effectively. The 3dB bandwidth of the loop is determined by the pole at the output of the error amp...
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    Help me decide whether I need to add another buffer to a LDO regulator

    Re: LDO question It really depends on how large your power transistor is. If the power MOS is large, you might need to add a buffer stage to push the non-dominant pole further. And also, adding buffer will help to improve your power supply ripple rejection.
  16. P

    Phase margin of opamp in bandgap reference

    Chopper stabilization can also reduce the offset voltage of the opamp.
  17. P

    A question about SKILL and OCEAN

    Hi wjxcom, I did not seem to find any mistakes in your script. That puzzled me too. I first learnt oceanScript from this website, http://rle-12-184.mit.edu/~homer/misc/ocean/ocean3.shtml. Look at the bottom of the page. There are some fprint statements followed by some drain(file) and...
  18. P

    A question about SKILL and OCEAN

    I did not go through your script in detail. From my experience, drwave is a wave instead of a value. Check your script to make sure that you are printing some value instead of waves. Hope that help.
  19. P

    what kind of simulation I should run for design bandgap

    When I ran a DC temp sweep, the bandgap seems to give the wrong DCOP solution. However, if I did a transient temp sweep with the start-up circuit, I got a reasonable curve. So can I conclude that the bandgap is working well? Thanks.
  20. P

    Frequency dependency of ESR value of capacitor (for LDO)

    esr for capacitor low frequency I am currently designing a LDO voltage regulator making use of the ESR value of the external compensating capacitor to make the regulator stable. It is well known that the ESR value helps to create a zero to stabilize the regulating loop. I got the impedance and...

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