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Recent content by monsoon

  1. M

    Feedback circuit analysis

    If you consider the feedback as a voltage signal (i.e output of the source follower), then the input must also be a voltage. To implement the feedback, the input voltage and the feedback voltage must be added. Two voltages cannot be added by connecting them together (as in this circuit), instead...
  2. M

    how to do dc mismatch analysis in virtuoso spectre(IC615)

    In ADE (or ADEXL) there should be a menu "Variables" => Edit. Give the variable name as sigma and value as 3.
  3. M

    Feedback circuit analysis

    Loop gain is 1+gm3*R. Input impedance is (1/gm2) /(1+gm3*R). Output impedance is R/(1+gm3*R). The circuit is a current controlled voltage source. Voltage is sensed at the output and current is fedback at the input. You can also find the impedances by usual methods of KVL/KCL. But while...
  4. M

    how to do dc mismatch analysis in virtuoso spectre(IC615)

    Just include the MC model files and define a variable sigma=3 in spectre.
  5. M

    [SOLVED] fully differential opamp veriloga

    The code seems to be right ( except perhaps a typo in the first line in Output stage- (vcm) instead of V(vcm) ). With resistive feedback, there should not be any problem. However you cannot use an opamp as in your test bench, without any feedback for DC. However, if you just want to see the...
  6. M

    Transfer function & high cutoff frequency

    In addition to the condition,Gm*R2>>C1*CL/(C2*C2), the other condition for the expression to be valid is that both C1 and CL >> C2. Examples you have taken do not satisfy these. If you do not want the constraint on CL (as in your examples), the approx transfer function has to be modified.(...
  7. M

    Transfer function & high cutoff frequency

    An approximate transfer function gives an intuitive understanding of the location of poles and zeros. Thus there location can be found by just looking at the circuit , without doing much maths. To have reasonable passband fh>>fl gives Gm*R2>>C1*CL/(C2*C2). Also under the condition C1 and CL >>...
  8. M

    Transfer function & high cutoff frequency

    The given transfer function is valid only under certain condition. Some observations 1) Even though there are three capacitances C1 ,C2 and CL, it will be a second order system (as pointed earlier) as the the capacitances are in series and hence only two independent conditions can be...
  9. M

    Digital design puzzle

    First see how an inverter can be implemented. With this XOR can be implemented as shown.
  10. M

    [SOLVED] Quad Cross couple PTAT bandgap reference generatorworking principle

    If you neglect the base currents, PTAT current expression comes as follows: Same current I flows through Q1 and Q2, So Vbe1 - Vbe2= Vt ln(A3/A1) , where Vbe1 is the base -emitter voltage of Q1 and like wise. or Vb1 -Ve1 -Vb2+Ve2=Vt ln(A3/A1) or Vb1-Ve1-Vb2=Vt ln (A3/A1) Similarly for Q3 and...
  11. M

    Continous Sigma Delta ADC- Choosing the proper DAC

    You may try the following things 1) Chose the test input signal bin such that the third harmonic also lies in the signal bandwidth. 2) Now verify with ideal DAC that you get the SNDR. 3) In the real DAC, replace the two mirrors with ideal current sources. Does the SNDR degrade? 4) In the real...
  12. M

    Continous Sigma Delta ADC- Choosing the proper DAC

    I had some questions , am not sure you have mentioned earlier. 1) What is the modulator order? 2) have you used optimized zeros? 3) What is the OSR?
  13. M

    Continous Sigma Delta ADC- Choosing the proper DAC

    If you can show both the spectrum in semi-log scale, it would be little more meaningful. Also mark if there are any harmonics in the spectrum.
  14. M

    About sampling instant of S/H

    Sampling instant is determined by Φ1p only. The reason being after Φ1p goes down, voltage across the sampling capacitor Cs cannot change because one of its terminal is floating. This is also the reason why there is no charge injection from the sampling switch.
  15. M

    Pre-Amplifier + Latch Overall Input-Referred Offset

    You refer to Razavi book. (chapter on noise and mismatch). Its not "more" precise. Random variables are characterized by both mean and variance. You can also search about gaussian random variables.

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