EE220 2024 Noise Analysis and Simulation: Difference between revisions

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(Created page with "* '''Instructions''': This activity is structured as a tutorial with an activity at the end. Should you have any questions, clarifications, or issues, please contact your instructor as soon as possible. * At the end of this activity, the student should be able to: # Perform noise simulations using NGSPICE. == Activity 1: NMOS Noise == Bias a 0.8V SLVT NMOS transistor with <math>V_{GS}=0.4\mathrm{V}</math> and <math>V_{DS}=0.4\mathrm{V}</math>. For a width of <math>1\ma...")
 
 
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* '''Instructions''': This activity is structured as a tutorial with an activity at the end. Should you have any questions, clarifications, or issues, please contact your instructor as soon as possible.  
* '''Instructions''': This activity is structured as a tutorial with an activity at the end. Should you have any questions, clarifications, or issues, please contact your instructor as soon as possible.  
* At the end of this activity, the student should be able to:
* At the end of this activity, the student should be able to:
# Perform noise simulations using NGSPICE.
# Perform noise simulations using Cadence Spectre using the GlobalFoundries 22nm FDSOI design kit.


== Activity 1: NMOS Noise ==
== Activity 1: NMOS Noise ==
Bias a 0.8V SLVT NMOS transistor with <math>V_{GS}=0.4\mathrm{V}</math> and <math>V_{DS}=0.4\mathrm{V}</math>. For a width of <math>1\mathrm{\mu m}</math> and a length of <math>L_{\min}</math>:
Bias a 0.8V SLVT NMOS transistor with <math>V_{GS}=0.4\mathrm{V}</math> and <math>V_{DS}=0.4\mathrm{V}</math>. For a width of <math>1\mathrm{\mu m}</math> and a length of <math>L_{\min}</math>:
* What is the resulting DC drain current?
* What is the resulting DC drain current?
* What is the transistor's <math>g_m</math> and <math>V^*=\frac{2I_D}{g_m}</math>?
Run a noise analysis from <math>1\mathrm{Hz}</math> to <math>1\mathrm{THz}</math>.
* Plot the drain current noise power spectral density, <math>\frac{\overline{i_{dn}^2\left(f\right)}}{\Delta f}</math>.
** Identify the regions where thermal noise and flicker noise dominates.
** What is the flicker noise corner?
** Estimate the value of <math>\gamma</math>.
** Estimate the value of <math>\frac{K_f}{C_{ox}}</math>
* What is the total integrated drain current noise power? 
Recall that the MOSFET drain current noise can be modeled as:
::<math>\overline{i_{dn}^2} = \frac{K_f I_D}{C_{ox} L^2}\frac{\Delta f}{f} + 4kT\gamma g_m \Delta f</math>
Change the length of the transistor to <math>2L_{\min}</math> and <math>3L_{\min}</math>. Identify and explain any changes in the drain current noise power spectral density.
* Repeat for the LVT and regular-VT NMOS transistors. Did you notice any differences in noise behavior?
== Activity 2: PMOS Noise ==
Repeat Activity 1 but with 0.8V PMOS transistors with the same sizes, and with <math>V_{GS}=-0.4\mathrm{V}</math> and <math>V_{DS}=-0.4\mathrm{V}</math>.
== Activity 3: Cascode Amplifier Noise Analysis ==
Consider the cascoded NMOS amplifier (biased with an ideal current source) shown in Fig. 1. Ignoring all other capacitances except <math>C_L</math>, and given the small-signal parameters <math>g_{m1}</math>, <math>g_{m2}</math>, <math>r_{o1}</math> and <math>r_{o2}</math>:
{|
| [[File:Cascode-noise.png|thumb|225px|Figure 1: A cascode amplifier.]]
|-
|}
# Calculate the small-signal gain of the cascode amplifier, <math>A_v\!\left(s\right) = \frac{v_{out}}{v_{in}}</math>. Assume <math>g_{m1}r_{o1}\gg 1</math> and <math>g_{m2}r_{o2}\gg 1</math>.
# Calculate the noise spectral density, <math>\overline{v^2_{out}\left(f\right)}</math>, and the total integrated output noise, <math>\overline{v^2_{out,T}}</math>. Assuming that <math>r_{o1}\rightarrow \infty</math> and <math>r_{o2}\rightarrow \infty</math>, and that the flicker noise is zero.
# Repeat (2) but with finite <math>r_{o1}</math> and <math>r_{o2}</math>. How does this affect the output noise?
== Activity 4: Input-Referred Noise ==
Given the gate-source capacitance, <math>C_{GS}</math>, of transistor <math>M_1</math> of the cascode amplifier in Fig. 1, calculate:
* The input equivalent voltage noise generator, <math>\overline{v^2_{i,eq}\left(f\right)}</math>.
* The input equivalent current noise generator, <math>\overline{i^2_{i,eq}\left(f\right)}</math>.
Note that when calculating the output noise, you can assume that <math>r_{o1}\rightarrow\infty</math> and <math>r_{o2}\rightarrow\infty</math>, but when calculating the gains, assume finite <math>r_{o1}</math> and <math>r_{o2}</math>.
== Report Guide ==
Write up a report (maximum of 5 pages including figures) answering the questions above. Include annotated graphs if needed.

Latest revision as of 06:52, 9 October 2024

  • Instructions: This activity is structured as a tutorial with an activity at the end. Should you have any questions, clarifications, or issues, please contact your instructor as soon as possible.
  • At the end of this activity, the student should be able to:
  1. Perform noise simulations using Cadence Spectre using the GlobalFoundries 22nm FDSOI design kit.

Activity 1: NMOS Noise

Bias a 0.8V SLVT NMOS transistor with and . For a width of and a length of :

  • What is the resulting DC drain current?
  • What is the transistor's and ?

Run a noise analysis from to .

  • Plot the drain current noise power spectral density, .
    • Identify the regions where thermal noise and flicker noise dominates.
    • What is the flicker noise corner?
    • Estimate the value of .
    • Estimate the value of
  • What is the total integrated drain current noise power?

Recall that the MOSFET drain current noise can be modeled as:

Change the length of the transistor to and . Identify and explain any changes in the drain current noise power spectral density.

  • Repeat for the LVT and regular-VT NMOS transistors. Did you notice any differences in noise behavior?

Activity 2: PMOS Noise

Repeat Activity 1 but with 0.8V PMOS transistors with the same sizes, and with and .

Activity 3: Cascode Amplifier Noise Analysis

Consider the cascoded NMOS amplifier (biased with an ideal current source) shown in Fig. 1. Ignoring all other capacitances except , and given the small-signal parameters , , and :

Figure 1: A cascode amplifier.
  1. Calculate the small-signal gain of the cascode amplifier, . Assume and .
  2. Calculate the noise spectral density, , and the total integrated output noise, . Assuming that and , and that the flicker noise is zero.
  3. Repeat (2) but with finite and . How does this affect the output noise?

Activity 4: Input-Referred Noise

Given the gate-source capacitance, , of transistor of the cascode amplifier in Fig. 1, calculate:

  • The input equivalent voltage noise generator, .
  • The input equivalent current noise generator, .

Note that when calculating the output noise, you can assume that and , but when calculating the gains, assume finite and .

Report Guide

Write up a report (maximum of 5 pages including figures) answering the questions above. Include annotated graphs if needed.