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.

How to calculate the value of a capacitor to maintain VCCOUT

Status
Not open for further replies.

snoop835

Advanced Member level 4
Joined
Feb 7, 2005
Messages
102
Helped
6
Reputation
12
Reaction score
3
Trophy points
1,298
Location
Penang, Malaysia
Activity points
1,370
Capacitor

Hi all,

As you can see in the attachment file, I tried to main the VCCOUT dc level when the input VCC droop to 0.5V and stay for few us and rise again to 1.8V. I used diode connected NMOS and capacitor so the VCCOUT = VCC - Vth. Can somebody tell me what is the equation to be used to calculate the value of the capacitor in order to maintain VCCOUT even when VCC has a droop?

Is there any other circuit that can perform the same function if not better since my circuit will have voltage drop because of the diode connected transistor.

I hope you guys can throw me some light on this.

appreciate any comments!

thanks

-snoop835-
 

alenhan

Junior Member level 1
Joined
Feb 27, 2006
Messages
17
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,410
Capacitor

Hi,
I think the drop is due to the charge sharing to the parasitic cap. from the diode connected NMOS, in
one clock cycle
C*(1.8-0.5)=(C+Cpar)*VCCOUT_min
so if the C is much larger than Cpar, the VCCOUT
can be more close to VCC-Vthn.
 

Syukri

Full Member level 5
Joined
Aug 9, 2005
Messages
252
Helped
24
Reputation
48
Reaction score
10
Trophy points
1,298
Location
Malaysia
Activity points
3,954
Re: Capacitor

try to use tansmission gate raher than nMOS switched
 

snoop835

Advanced Member level 4
Joined
Feb 7, 2005
Messages
102
Helped
6
Reputation
12
Reaction score
3
Trophy points
1,298
Location
Penang, Malaysia
Activity points
1,370
Re: Capacitor

Hi syukri,

Do you mean replacing the diode with transmission gate...How to use transmission gate to replace the nmos diode connected? Pls elaborate....

appreciate your help.

thanks
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top