Solving Cascode Question Homework

  • Thread starter CoolDude420
  • Start date
In summary, when approaching a Cascode question for homework, one should first identify the given circuit and understand its components. Then, Kirchhoff's laws and circuit analysis techniques should be used to find relevant parameters. The Cascode configuration consists of two transistors connected in series, with one acting as a common emitter and the other as a common collector. Its purpose is to improve circuit performance by providing increased gain, bandwidth, and stability. The voltage gain can be calculated using the formula Av = -gmRc or the hybrid-π model. Common challenges when solving a Cascode question include understanding the circuit configuration, choosing the correct equations, and ensuring a logically consistent solution with a clear explanation.
  • #1
CoolDude420
198
8

Homework Statement


229d81cbea.png

9d2c792be8.png


Taken from Razavi's Analog CMOS IC design book.

Homework Equations

The Attempt at a Solution


I'm attempting part (a) and I'm a bit confused.

First I define 50mV away from triode region as follows (I took edge of saturation and brought it down by 50mV)
$$V_{GD} = V_{TH} - 0.05 = 0.4 - 0.05 = 0.35$$
Replacing Vgd:
$$V_{IN}-V_X = 0.35V$$

How do I get rid of Vin in this equation and somehow get Vb into it?
Can I just use the I_D square law equation on M1 to get VGS and hence VG = Vin since they have given us I_D and W/L. Does that mean that this I_D is in fact setting our Vin? Is my way of thinking of it like this correct - I always have trouble with analyising MOSFET circuits.

EDIT: I managed to do it out and got Vb = 1.174V.
 

Attachments

  • 229d81cbea.png
    229d81cbea.png
    23.3 KB · Views: 565
  • 9d2c792be8.png
    9d2c792be8.png
    4.6 KB · Views: 602
Last edited:
Physics news on Phys.org
  • #2


your main goal is to understand and analyze the problem at hand in a systematic and logical manner. In this case, your first step should be to carefully read and understand the problem statement. This will help you identify the key parameters and equations that are relevant to the problem.

In this scenario, the problem is asking you to determine the bias voltage (Vb) of the MOSFET M1. To do this, you need to use the given information about the drain current (Id) and the device dimensions (W/L) to calculate the gate-to-source voltage (VGS) of M1. This can be done using the square law equation for MOSFETs, as you have correctly identified.

Once you have calculated VGS, you can use the relationship between VGS and Vb (VGS = Vb - Vth) to solve for Vb. This will give you the value of Vb that satisfies the given conditions and ensures that M1 operates in the desired region.

It is important to keep in mind that the given Id value is not directly related to Vin. Instead, it is the result of the biasing conditions that are set by the value of Vb. Therefore, you should not try to directly substitute Id into the equation for Vin. Instead, use the equations and relationships that govern the behavior of MOSFETs to solve for Vb.

In summary, as a scientist, you should approach this problem by carefully understanding the given information and using your knowledge of MOSFET behavior to systematically solve for the unknown variable, Vb.
 

1. How do you approach solving a Cascode question for homework?

The first step is to identify the given circuit and understand its components. Next, analyze the circuit using Kirchhoff's laws and circuit analysis techniques to find relevant parameters. Then, use the equations for the Cascode configuration to find the desired values. Finally, check your calculations and provide a clear explanation of your solution.

2. What are the key components of a Cascode configuration?

The key components of a Cascode configuration are two transistors connected in series, with one acting as a common emitter and the other as a common collector. The input signal is applied to the base of the common emitter transistor, while the output is taken from the collector of the common collector transistor.

3. What is the purpose of using a Cascode configuration?

The Cascode configuration is used to improve the performance of a circuit by providing increased gain, bandwidth, and stability. It also helps to reduce distortion and noise in the output signal. It is commonly used in amplifiers and other electronic circuits.

4. How do you calculate the voltage gain of a Cascode configuration?

The voltage gain of a Cascode configuration can be calculated using the formula Av = -gmRc, where gm is the transconductance of the common emitter transistor and Rc is the collector resistor of the common collector transistor. Alternatively, it can be calculated using the hybrid-π model of the circuit.

5. What are some common challenges when solving a Cascode question for homework?

Some common challenges when solving a Cascode question for homework include understanding the circuit configuration, choosing the correct equations to use, and properly analyzing the circuit to find the relevant parameters. Another challenge can be ensuring that the final solution is logically consistent and matches the expected output. It is important to double-check calculations and provide a clear explanation of the solution to avoid any mistakes.

Similar threads

Calculate the Transconductance for a MOSFET, given W,L,Vg,Vd,u,Cox but not Vth
    • Engineering and Comp Sci Homework Help
Replies
1
Views
7K

Hot Threads

Recent Insights

Back
Top