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Type: Posts; User: frankrose

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  1. Replies
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    Closed: Re: Noise Source generator Circuit

    Any single resistor has thermal noise with gaussian probability density function, but noise is not a single frequency. Do you need 6HGz bandwidth for the power spectral density? What would you like...
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    Closed: Re: common mode feedback question

    yefj, you have basic problem with understanding what common mode feedback does. It has no connection to mismatch of currents, CMFB sets/tunes both currents in a way that the main OPAMP will operate...
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    Closed: Re: folded cascode with gm/id

    M1 is half of the diff.pair, so its current is half of the tail current. Thus M3,M4 have a 80uA current. You have to know the ratio of M11/M4 ratio to know how much is the current of M11, which...
  4. Closed: Re: Switch size in a resistive trim network ?

    Yes, it means. Also, no, don't place R to the top. It is more effective if you can shunt R (the samllest resistance unit value) with the lowest NMOS. The lowest NMOS can produce the lowest Ron to...
  5. Closed: Re: Switch size in a resistive trim network ?

    Use minimum L, and choose the minimal W with the following conditions:
    - lowest gate voltage applied
    - slow-slow (SS) process
    - cold temperature (but maybe the hottest temp is also recommended to...
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    Closed: Re: Fast amplifier using one stage OP AMP

    How much is the expected rising/falling time value? Why do you need 5V amplitude, what is your load? Any other specifications (consumption, delay, etc.)?
  7. Closed: Re: Optimum strategy to layout MOSFET cascoded mirror

    1. first approach is pretty good, I suggest it. Match mirrors and cascode devices separately is more effective. Cascodes and mirrors are not the same size usually, why would you match them together?...
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    [SOLVED]Closed: Re: Down-conversion Mixer

    You are not wrong, active can produce more noise, but if you don't gain at the begining of the amplifier chain, the following much more noisy circuits will have bigger contribution. Passive mixer's...
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    [SOLVED]Closed: Re: Down-conversion Mixer

    Active will give much better noise figure, that is why so popular, consumption is not a trade-off if you need -110dBm sensitivity for the receiver chain.

    Actually I don't know, but big advantage...
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    Closed: Re: Gain and Phase margin problem

    I don't want to repeat last comment, all of it is true, you have basic problems with your circuit. Never use DC sources for example to bias current generators, cascodes are ok, but I am almost sure...
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    Closed: Re: Gain and Phase margin problem

    What kind of 2nd stage do you have? Could you show more details (bode diagram, schematic)? 150° means stable operation, however it is suspicious value. Probably you did something not usual with the...
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    Closed: Re: Fast static CMOS comparator circuit

    aicdesign.org has some free courses online by P.E.Allen. Browse for it.
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    Closed: Re: Trans-impedance Amplifier using OTA.

    73dB is extreme high value for closed loop gain. It is not a surprise you reached 20kHz bandwidth with some hundred uA consumption. And with 73dB closed loop gain your output offset caused by...
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    Closed: Re: Noise analysis for diff amp in Cadence

    BW is the desired signal frequency range. It can be the OPAmp bandwidth, or if you have any filter with lower bandwidth use that value. I guess if you have low noise amplifier you want to amplify a...
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    Closed: Re: Noise analysis for diff amp in Cadence

    In OPAmp datasheets normally the input referred noise is given. You can get the value of it with simulation of the power spectral density function (PSD).
    Connect your OPAmp as unity gain buffer,...
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    Closed: Re: Noise analysis for diff amp in Cadence

    It depend on the circuit. Linear diff.pair should be checked with AC noise or pnoise analysis, for switched diff.pair pnoise or transient noise should be used. Otherwise I don't understand what are...
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    Closed: Re: current mirror diode

    Browse for common-centroid arrangement.
  18. Closed: Re: Problem of impedance matching of Gilbert cell mixer

    Firstly, is it integrated or not? Integrated mixer's input is connected to a low noise amplifier (LNA) usually, matching between them is not necessary until the frequency is not too high and...
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    [SOLVED]Closed: Re: Average vs RMS load-current for LDO design

    In my opinion RMS is a fancy average calculation. The integral symbol and the division with a time period means the average calculation in the equation. The squared signal only relates to convert...
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    [SOLVED]Closed: Re: Average vs RMS load-current for LDO design

    Digital load current is like noise, as described in #5, and noise is characterized with its RMS value.
    I agree with the difference, but SCR example is misleading now I think, or maybe it is answer...
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    [SOLVED]Closed: Re: Average vs RMS load-current for LDO design

    Hi,

    Use RMS. It is the most talkative to estimate the load current with its all DC and AC components, and some overdesign is still necessary.
    For example the voltage ripple on your LDO output...
  22. [SOLVED]Closed: Re: PWM applied to load while current limiting on load simultaneously

    If you know, that from fix DC 12V the current consumption is already too high why would you apply higher voltage?
    BUCK and BOOST generate DC voltage with relatively small AC ripple, it is not...
  23. [SOLVED]Closed: Re: PWM applied to load while current limiting on load simultaneously

    Q1 in your current limit circuit is always switched off I think, doesn't look good.
    Why don't you look for an IC? Basically you need a DCDC converter with adjustable output voltage and current...
  24. [SOLVED]Closed: Re: OTA 2 stage (folded cascode + common source)

    M3 and M4 are not cascoded. They should be. Otherwise it won't work well.
    Don't bias NMOS devices with PMOS diodes, it is a bad idea, they don't vary with process together.
    Source followers add...
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    Closed: Re: Simple CMFB using two transistors only

    It seems extremely mismatch sensitive. The size or threshold difference generated error of the added devices is amplified by the folded cascode stage, I think it is not a practically viable solution.
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