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Type: Posts; User: sutapanaki

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  1. Closed: Re: Class AB fully differential amplifier design issue

    From what I see M7/M12 are just providing level shift. M6 and M5 are most probably same or ratioed. If Vds of M6 (defined by one Vgs above gnd) is bigger than Vds of M5 (defined by the output CM...
  2. Closed: Re: Fully-Differential folded cascode amplifier with enhanced gain

    Yes. Try it and let me know what you get.
  3. Closed: Re: Fully-Differential folded cascode amplifier with enhanced gain

    I see this time it worked. So, just a clarification. The replica is there to just make sure the operating conditions for M5a and M3a are good with the cascode bias of M5a. Then, for the common-mode...
  4. Closed: Re: Fully-Differential folded cascode amplifier with enhanced gain

    Somehow, the picture didn't show. Let's try again.

    156438
  5. Closed: Re: Fully-Differential folded cascode amplifier with enhanced gain

    You need to create a voltage reference for your CMFB circuit for the aux amps that puts the main amplifier cascodes in the right operating conditions. An idea could be with a replica circuit like in ...
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    Closed: Re: DAC unit cap selection for SAR ADC

    Using the kT/C noise to calculate the unit cap is a reasonable approach. MOM caps usually used in the design of the cap dac for SARs match pretty well, maybe up to 10 bit accuracy and they keep their...
  7. Closed: Re: Fully-Differential folded cascode amplifier with enhanced gain

    You should not try to somehow fudge the common-mode voltage of the aux amplifier. Best is to create a replica circuit from similar transistors as M3 and M5, with a current that's also similar (DC...
  8. Closed: Re: Dynamic Comparator Input Referred noise

    How do you calculate the noise of that comparator?
  9. Closed: Re: Problem in saving data during DC sweep simulation in Cadence Virtuoso

    It is true that transient may exercise time behavior of the circuit but this is in case if you change you VIC too fast. If the change is slow enough, then it is pretty much like DC.
  10. Closed: Re: Transistor region of operation in operational amplifier

    It is rather the concept of threshold voltage and what really threshold means, as well as how it is defined. Because you can see that even in weak inversion there is some conduction in the...
  11. Closed: Re: Problem in saving data during DC sweep simulation in Cadence Virtuoso

    Instead of doing a DC sweep, can you do a transient sweep of your VIC and run .ac at different points (time points which you have to enter by hand) of the transient sweep?
  12. Closed: Re: Transistor region of operation in operational amplifier

    Whether the region after 0.7 on your plot represents triode, I don't know. It depend on the value of the Vds that you have. Up until Vgs=Vds+Vth the transistor is supposed to be in saturation. In...
  13. Closed: Re: Transistor region of operation in operational amplifier

    Provided your transistor is in saturation, then that Vgs voltage puts it into moderate or close to moderate inversion. In this plot it is very obvious where the weak inversion is, the flat part...
  14. Closed: Re: Transistor region of operation in operational amplifier

    Oh, that's easy. Just open a text file, write in it

    save * sigtype=all

    Then save it with any name and extension .scs. That's it.
  15. Closed: Re: Transistor region of operation in operational amplifier

    Look at this old discussion. The method of plotting gm or gm/id is summarized in reply #12


    https://www.edaboard.com/showthread.php?15832-How-to-do-this-in-IC5

    - - - Updated - - -

    That...
  16. Closed: Re: Transistor region of operation in operational amplifier

    Now, plot and show here gm/Id vs Vgs.
  17. Closed: Re: Transistor region of operation in operational amplifier

    gm/Id is just one method to use for design which is good for newer technologies but it doesn't mean it can't be used with older technologies too. What I was saying before was really related to what...
  18. Closed: Re: Transistor region of operation in operational amplifier

    They say you leave the weak inversion region at about 3 to 4x kT/q.

    However, I don't think you design exclusively based on Vov. It shouldn't be your primary design variable, although sometimes it...
  19. Closed: Re: Transistor region of operation in operational amplifier

    One approach I use (whenever I need to know the region of operation, which is actually not so often) is to plot gm/Id vs Vgs. The curve kind of saturates for small Vgs (even Vgs < Vth) and that's...
  20. Closed: Re: -3db frequency of the op-amp open loop gain

    We do design for unity GBW and DC gain and in the case of a -20db/dec roll-off the -3db frequency in the open loop transfer comes as a consequence. If you imagine your opamp as an ideal integrator,...
  21. Closed: Re: Deaign of low ON resistor CMOS transmission gate

    Why do you need to limit yourself to only using minimum L transistors? You use the L that you need for your application. Usually it is the min L, because it guarantees faster switches and smaller...
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    Closed: Re: Sooch current mirror

    Actually, even the mirror with the stacked transistors can work with a single input current but it needs a small start-up circuit and it can be done without consuming extra.
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    Closed: Re: Sooch current mirror

    I don't think you should stick to using the same size transistors in the stack as they are in the cascodes of the mirror. In your figure B both cascodes and stacked transistors are 120/1. While it is...
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    Closed: Re: Sooch current mirror

    Yes, that current mirror with resistors I have used before. The cascode voltage is then Vgs+IR. However, I still think that the version with the stack transistors should track better.
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    Closed: Re: Sooch current mirror

    Perhaps this mirror is ok with 3.3v supply. At the diode side you have 2Vgs from gnd up and this reduces the compliance voltage for the P current source. This can be a problem in technologies that...
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