Looking for adjustable slew rate circuit

[Wenye]

Slew rate control

Hi All,

Does anyone has idea in adjustable slew rate circuit.
I need a circuit that can adjust slew rate of rising and falling edge separately. And the adjustable rate from 1ns to 100ns in 0.5 or 1ns per step.

Does anyone has any idea ?

Thank you in advance!

Wenye

 

[electronrancher]

yup - use a current source, and increase the current for faster slew. Anytime you mess with slew, you gotta know the capacitance on the output. (whatever node is slewing)

If you don't know the capacitance, you gotta add a cap big enough to be the main event (maybe 100pf if you expect to drive a bunch of logic gates, but dunno how many)

now compute slew with I=C(dV/dT). You wanna slew your 100pf from 0-5v in 100ns? -> 5mA.
10ns? 50mA
1ns? 500mA
0-1v in 1ns? 100mA
0-15v in 10ps? 150A. This gets tough up here.

 

[Wenye]

Re: Slew rate control

Hi Electronrancher,

First, thank you for your reply.

U idea is right and heuristic... Load capacitance (include pcb distributed capacitance) is around 50pF. But as my knowledge to drive a current source which is run in very high speed ( setting time of output current is lower then 1ns ) is a very difficult job.

Could u pls give me any idea how to do...

Wenye

 

[radix]

Re: Slew rate control

Wenye,

What's your application and technology(cmos, bipolar, etc...)?

Even though you say analog circuit design I've seen people call designing cmos output drivers "analog design".

Radix

 

[airace]

Re: Slew rate control

This paper may be of help to you...
it is on a idea for a o/p buffer with adaptive slew control
mechanism

regards

 

[tlbb]

Re: Slew rate control

Usually I/O circuits has slew rate requirement. Check those reference.

Basic ESD and I/O Design
by Sanjay Dabral (Author), Timothy Maloney (Author)

has some sample circuits.

Basic ESD and I/O Design

 

[mukeshk]

Re: Slew rate control

Look for source cross coupled opamp topology..
Here u can control the positive and negative slew rates seperately..

 

[alphi]

Re: Slew rate control

hi,mukeshk
can you supply some articles about"source cross coupled opamp topology"

 

[opamp741]

Re: Slew rate control

Check page no 390 of Allen Holberg..
Update me with ur status..

 

[opamp741]

Re: Slew rate control

Check page no 390 of Allen Holberg..
Update me with ur status..

 

[opamp741]

Re: Slew rate control

Check page no 390 of Allen Holberg..
Update me with ur status..

 

[alphi]

Re: Slew rate control

do you use it for electronic load?

 

[opamp741]

Re: Slew rate control

Ur question is not clear..Or may be lack of knowledge at my side..