Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

What is the purpose of this "VD=VS=GND" MOSFET in the circuit

Status
Not open for further replies.

bhl777

Full Member level 6
Full Member level 6
Joined
Sep 30, 2008
Messages
363
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,296
Activity points
5,140
Hi All, when I read some circuit, I often saw one block like the picture below. Can anyone teach me what is the purpose of this "VD=VS=GND" MOS? Thank you!
VDS=0.PNG
 

as far as i understand the circuit, i will try to explain things:
1. by Vd = Vs = GND means, drian voltage = source voltage = 0V i.e. GND, as seen from circuit, its pretty straight forward.
2. now replacing mosfet with its equivalent circuit, the significant thing is gate to channel capacitance i.e. a mosfet based variable capacitance is prominant at that circuit point.
3. the equivalent circuit for mosfet, between drain and source is transresistance and stray capacitance, where both will decrease when applied i/p voltage gate is higher, so in case if ground has high amount of surges or induced high freq emf, the lower stray capacitance and transresistance will keep it in GND.
I cant see any other significance of mosfet but i still try to analyse it.

hope that helps.
 
  • Like
Reactions: bhl777

    bhl777

    Points: 2
    Helpful Answer Positive Rating
Hi
Its a MOSCAP: The transistor is used as a capaciatance
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top