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Recent content by calculus_cuthbert

  1. C

    Difference between LDO and opamp

    Hi, I have some basic questions regarding LDO and opamp based amplifiers: 1. When is a LDO used and why can't an opamp based amplifier be used? For e.g. I came across a sensor analog front end system. A bandgap was designed to generate a reference voltage of ~1.2V. But the ADC needed a 2.4V...
  2. C

    What is the correct way of simulating input offset voltage

    I am actually simulating the input offset voltage of a comparator. Do you think I should use the first method for comparators because comparators are not connected in unity gain configuration? thanks a lot!
  3. C

    What is the correct way of simulating input offset voltage

    So according to your post: With my first method I got 7.11mV and my gain is 1590 so my input referred offset will be (7.11m/1590) = 4.46uV But this does not match the 600uV I am getting with the second method. This is why I am confused. I thought with the first method we get the output offset...
  4. C

    What is the correct way of simulating input offset voltage

    Hi Milad-D, Thanks for your reply. Right now I am measuring systematic offset. How do you say both ways are correct. My answers don't match up. With the first method do i need to divide it by the open loop gain? Even by doing that my answers don't match.. So I am not sure which method to use..
  5. C

    What is the correct way of simulating input offset voltage

    Hi all, I have a deadline to meet and I really need some help. What is the correct way of simulating input offset voltage. I referred two books: First Method says: ground the inverting terminal and make a dc sweep on the non-inverting terminal and check the DC transfer characteristic. The...
  6. C

    [SOLVED] Problem designing Opamp

    Is there a reason why you have designed the two stages separately? What kind of second stage are you using? and is your first stage a diff pair with current mirror load?
  7. C

    Differential gain of a diff pair

    Hi, I had a very basic question: For a MOS diff pair: two input NMOS transistors with equal gm and with load resistor Rd what is the differential gain: so is (vout1-vout2)/(vin1-vin2) = 2(gmRd) ? this leads to my next question: For a fully differential amplifier is the gain twice the single...
  8. C

    Differential signaling, Common mode rejection , matching

    Hi, I had a couple of questions of differential signaling and calculations for common mode rejection ratio. How do I calculate how much of the common mode noise is seen as a differential signal on the two inputs because of mismatch in the input resistance and capacitance? Please help!
  9. C

    How much CMRR is required

    Hi, I am trying to some initial calculations for requirements of a receiver. For a pre-amp (differential) the input signal voltage is 0.2V (voltage spike) and the width of the spike is ~ 500ps. The common mode noise signal is 0.5V (voltage spike) and the width of this spike is also 500ps. How...
  10. C

    How to calculate power consumed by an IC

    Hi, I had a very simple question regarding power consumption calculations of an amplifier. When the power consumption of an amplifier is stated in a data sheet how is it calculated? Is it Irms ( drawn by the circuit) multiplied by supply voltage? Thanks
  11. C

    Montecelli class AB output stage

    I have seen it but i don't quite understand it. Could you please explain in more detail?
  12. C

    Montecelli class AB output stage

    Hi, I am trying to understand the Montecelli class AB output stage. Can someone please explain it to me and how to design it. thanks
  13. C

    Startup circuit for PTAT current reference

    Thanks Palmeiras, Yes I think the aspect ratios were different. I guess my understanding was the the temperature coefficient should be same no matter what the aspect ratios were. So they would just be parallel lines having the same slope. So I had another question regarding the slope of the...
  14. C

    Startup circuit for PTAT current reference

    Thanks everyone for the suggestions and comments. I have attached a schematic of the PTAT current reference and start up circuit that I designing. One problem that I am facing is that the positive slope of the currents ID1 and ID2 are different. Shouldn't the slopes be the same? The current...
  15. C

    Startup circuit for PTAT current reference

    Hi, Could someone please explain why start up circuit is needed for a seld biased (bootstrapped) PTAT current reference? And I would really appreciate it if someone could give me a schematic of a start up circuit for the above. Thanks.
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