Noise in Cascode Stage - Amplifier Fundamentals - Analog & Mixed VLSI Design

TL;DR

This video discusses the impact of noise in the cascode stage and how it affects the output at different frequencies.

Transcript

hello everyone in this video we will study about noise in cascode stage consider the cascode stage of figure is shown below here since at low frequency the noise current of n1 and rd mostly flows through rd the noise contributed by these two devices is quantified as in common source stage okay so we can write it as dna whole square due to m1 and rd... Read More

Key Insights

• ⚾ Noise in the cascode stage is quantified based on the noise current of N1 and Rd.
• 😘 Device M2 has negligible impact on the output at low frequencies.
• ✋ The capacitance at node X affects the output noise and reduces gain at higher frequencies.
• ✋ The cascode stage can significantly increase input referred noise at high frequencies.
• ℹ️ Thermal noise is the main source of noise in the cascode stage.
• ❓ The flicker noise of M1 is neglected in the calculations.
• ⚡ The video discusses the voltage gain from the input to the output and its relation to node X capacitance.

Questions & Answers

Q: How is the noise current of N1 and Rd in the cascode stage quantified?

The noise current of N1 and Rd is quantified as dna whole square and is given by 4kt gamma by gm plus 1 upon gm 1 square r.

Q: Why does device M2 have a negligible effect on the output at low frequencies?

Device M2 has a negligible effect because when channel length modulation in M1 is neglected, the sum of noise current and drain current in M2 is equal to zero, hence not affecting Vnout.

Q: How does the capacitance at node X affect the output noise and gain at higher frequencies?

The capacitance at node X increases the output noise and reduces the gain from the main input to the output by shunting the signal current produced by M1 to ground.

Q: What is the main source of noise in the cascode stage?

The main sources of noise in the cascode stage are the thermal noise due to M1 and the resistor, while the flicker noise of M1 is neglected.

Summary & Key Takeaways

• The video explains how noise from devices N1 and Rd in the cascode stage is quantified and calculated.

• It describes the negligible effect of device M2 on the output at low frequencies.

• The video also discusses how the capacitance at node X reduces gain and increases noise at higher frequencies.