Type: Posts; User: frankrose

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  1. 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...
  2. [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...
  3. [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...
  4. [SOLVED]Closed: Re: Average vs RMS load-current for LDO design


    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...
  5. [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...
  6. [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...
  7. [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...
  8. Replies

    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.
  9. Closed: Re: Current Reference in Sub-Threshold region

    Extra circuitry doesn't need big consumption, rather area. And it is more effective.
  10. Closed: Re: Current Reference in Sub-Threshold region

    Probably it is possible to operate at the edge of the threshold voltage, but deep sub-threshold is not recommended becasue of worse matching between the circuit and the output current mirror....
  11. Closed: Re: Determining output impedance in LT SPICE

    LTSpice is freeware, Cadence Spectre is the high-end, operating point reading of DC sweep is a luxury comfort I guess. Like AC stability analysis.
    But with some struggling you can characterise...
  12. Closed: Re: Charge Pump with unity gain amplifier (Bootstrapping Charge Pump)

    I don't see attachments...
  13. Replies

    Closed: Re: What are biasing circuits?

    Bias circuit sets DC operating points of devices. It is necessary to reach good linearity, or fast operating speed. A simple base resistor can be bias circuit. And all above are true, if you use the...
  14. Closed: Re: Biasing an array of current steering DACs

    You can mirror the current with 128 branches. It won't be worse from mismatch and start-up viewpoints and actually the area will be smaller compared to cascaded NMOS/PMOS mirror stages.
    If you want...
  15. Replies

    Closed: Re: "Ideal" differential amplifier in SPICE

    With ideal source don't care about common mode voltage. Common mode DC is normally used to set operating point for input/output transistors, without devices it will increase the complexity. If you...
  16. Closed: Re: Fully-Differential folded cascode amplifier with enhanced gain

    Imagine that M5-M8 are simple cascode transistors, and the AUX-N/AUX-P set now the cascode bias voltages, which should be a Vgs+Vdsat for a folded-cascode amp with not enhanced gain to reach the...
  17. Closed: Re: Noise Figure budget analysis for power combiner & divider

    for every passive device the NF equals its own attenuation, so splitters have 3dB, and at combiners are not guaranteed the input signals are the same, thus they should have 0dB in that case I guess.
  18. Replies

    Closed: Re: DAC unit cap selection for SAR ADC

    I am sad I don't have knowledge about it, it sounds interesting, but your equation seems vague in terms of left side / right side units.
    I guess there are some extra behind them, which you...
  19. Closed: Re: How to take ESD and pad capacitances into consideration during design

    Connect them to ground, it is enough. ESD is normally at the direct input of the chip and builded into the pad between input & VDD/VSS, sometimes secondary ESD is implemented at the gates which are...
  20. Replies

    Closed: Re: Analog Layout - Sharing source/drain

    1) not exactly true, useage of fingers has the advantage they need less area and the parasitics are smaller. disadvantage can occour when matching is the main viewpoint, with odd and small number...
  21. Closed: Re: [Cadence ADE XL] Optimize a Common Source Amplifier to 15dB gain via Corner Analy

    I recommended you the section a) of below picture. The bias circuit is M3(diode connected) + the current source, the DC coupling device is R, and the AC coupling device is C. You should replace (or...
  22. Closed: Re: [Cadence ADE XL] Optimize a Common Source Amplifier to 15dB gain via Corner Analy

    If you need 15dB DC gain above circuit is pretty useless, only at the ouput transition you have gain (derivate of your curves), which is input gate threshold voltage dependent, thus corner dependent....
  23. Closed: Re: Modelling power supply for cadence simulations

    VDC is ideal, through big part of the the full design phase it is should be enough. However if you know that your supply will be poor from any standpoint or your circuit is too sensitive it is...
  24. Closed: Re: Modelling power supply for cadence simulations

    These are package parasitics, not source model components. Source is not depending on the package, it should depend on what are you using as a source (LDO,battery,SMPS). And in the package the model...
  25. Replies

    Closed: Re: Ring Oscillator Phase Margin Question

    I guees you set wrong operation point for the stability analysis where the gain is negligible. Without more info hard to say correct answer...
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