Calculate Ro for CS MOSFET Amp using V'A, L, and ID | Homework Solution

A.In summary, the question is asking for the Ro value of a CS MOSFET amplifier given V'A, L, and ID. The formula for Ro is V'A*L/ID. After plugging in the values, the result is 4*10^-8. However, the book gives a different answer of 40kΩ. After further examination, it is discovered that V'A is in units of V/μm, so the correct calculation is (10*V/μm)*(0.4*μm)/(100*μA), which simplifies to 40,000 ohm or 40kΩ.
  • #1
vermin
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Homework Statement


Supposed to find Ro for a CS MOSFET amp given V'A=10V/μm, L=0.4μm, and ID=100μA.

Homework Equations



Ro=ro=V'A*L/ID

The Attempt at a Solution



I say that ro=10μ*0.4μ/100μ=
10*10^-6*0.4*10^-6/100*10^-6
= 4*10^-8

Book says "10x0.4/.1=40kΩ"

.. what exactly went into that? for one thing (10*0.4)/.1 does not = 40,000.

also if you multiply something in micrometers by something in micrometers, then divide by something in microamps, you should end up with a very small number, I think.

I'm sure 40kΩ makes sense somehow but they're doing a bad job of explaining it.
 
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  • #2
Nevermind, I got it. V'A was in units of V/um, so really 10*(V/um)

[(10*(V/um))(0.4*um)]/(100*uA)=(10*V*0.4)/(100*uA)=40,000 ohm

^ because the um cancels out in numerator, ^ becomes just 4 V
 

Related to Calculate Ro for CS MOSFET Amp using V'A, L, and ID | Homework Solution

1. What is the formula for calculating Ro in a CS MOSFET Amp using V'A, L, and ID?

The formula for calculating Ro in a CS MOSFET Amp is Ro = V'A / (L * ID), where V'A is the Early voltage, L is the channel length, and ID is the drain current.

2. What are the units for V'A, L, and ID in the formula for calculating Ro?

V'A is typically measured in volts (V), L is measured in meters (m), and ID is measured in amperes (A).

3. How can I determine the values for V'A, L, and ID in order to calculate Ro?

V'A can be determined from the datasheet of the MOSFET you are using. L can also be found in the datasheet or can be measured directly using a ruler. ID can be calculated using Ohm's Law (ID = VD / RD) or can be found in the datasheet.

4. Can I use the same formula to calculate Ro for other types of MOSFET amplifiers?

No, the formula for calculating Ro in a CS MOSFET Amp is specific to that type of amplifier. Different types of MOSFET amplifiers may have different formulas for calculating Ro.

5. How important is it to calculate Ro in a CS MOSFET Amp?

Calculating Ro is essential in understanding the performance of a CS MOSFET Amp. It helps determine the amount of voltage and current drop in the circuit, and can also affect the stability and gain of the amplifier. It is important to accurately calculate Ro in order to design a reliable and efficient circuit.

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