Powered by Invision Power Board


Forum Rules Forum Rules (Please read before posting)
  Reply to this topicStart new topicStart Poll

> Double Integrator?, HOWWWWWW????
cuallito
Posted: May 07, 2010 07:49 pm
Reply to this postQuote Post


Newbie
*

Group: Members+
Posts: 6
Member No.: 29,340
Joined: May 05, 2010




I'm trying to design a double integrator circuit, but I'm having trouble. Chaining two opamp integrators together doesn't work, even with an opamp buffer between them. How can I make one?


--------------------
Say: "qui-YEE-toe"! It's spanish!
PMEmail Poster
Top
cuallito
Posted: May 07, 2010 11:13 pm
Reply to this postQuote Post


Newbie
*

Group: Members+
Posts: 6
Member No.: 29,340
Joined: May 05, 2010




Okay, came up with this

user posted image

Have two problems with it though:

1) It's unstable, even with a signal that has no DC component.
2) How would you implement the current "drain" on the second OPAMP using actual parts?

Thanks for any help...

This is the code if you want to plug it into the falstad circuit sim:

CODE

$ 1 5.0E-6 10.20027730826997 55 5.0 50
r 112 208 176 208 0 1000.0
c 176 144 272 144 0 1.0E-5 -1.1296343561459452
w 176 208 208 208 0
w 176 144 176 208 0
w 272 144 272 224 0
v 112 208 112 272 0 2 40.0 5.0 0.0 0.0 0.5
R 80 272 64 272 0 0 40.0 1.0 0.0 0.0 0.5
w 80 272 112 272 0
w 112 272 208 272 0
w 208 272 208 240 0
w 272 224 288 224 0
a 208 224 272 224 0 15.0 -15.0 1000000.0
t 288 224 352 224 0 1 -7.412061529358775 0.5864899872935012 100.0
R 352 128 352 112 0 0 40.0 10.0 0.0 0.0 0.5
r 352 128 352 208 0 300.0
r 352 240 432 240 0 1000.0
a 448 256 528 256 0 15.0 -15.0 1000000.0
w 432 240 432 192 0
w 528 192 528 256 0
w 608 320 608 304 0
w 432 240 448 240 0
R 448 272 448 336 0 0 40.0 0.0 0.0 0.0 0.5
c 432 192 528 192 0 1.0E-6 9.419127428052535
i 432 240 432 320 0 0.0035
g 432 320 432 336 0
o 18 64 0 35 16.36695303948071 0.005114672824837722 0 -1
o 4 64 0 35 10.0 0.05 1 -1


--------------------
Say: "qui-YEE-toe"! It's spanish!
PMEmail Poster
Top
Sch3mat1c
Posted: May 08, 2010 01:25 am
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 19,534
Member No.: 73
Joined: July 24, 2002




If the op-amp models have ideal outputs and no voltage limts, two chained integrators will indeed produce the correct result. You may not be able to see this if the result runs away.

Without global feedback, integrators have a nasty habit of running away due to very small offsets. For this reason, a low frequency pole is always present, e.g., a very large resistor across the integration capacitors, or a long time constant from output to input (or a "bias servo" which does the same thing).

Tim


--------------------
Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.
PMEmail PosterUsers Website
Top
cdstahl
Posted: May 08, 2010 01:54 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Trusted Members
Posts: 1,009
Member No.: 11,808
Joined: November 04, 2007




keep in mind that sim, with no initial values, can decide that the initial voltage on C1 is 4BV, and C2 is -700MV.


anyways, if this is in relation to the DAC thread, I'll restate my post -- you're trying to force what you want into something that works well. For a sim, it can work, but its not a good practical design. As such, the more you force this to work with real parts, the more time (and maybe money) you'll waste with expensive parts and such.

Others have thought for many years on good ways filter things using opamps. They've also stepped past the math part to the part where the topology is analyzed for the practical limitations of the parts. nuhertz's website has some of the most straightforward descriptions of why you would choose one 3-opamp topology over another 3-opamp topology over a 1-opamp one.
PMEmail Poster
Top
0 User(s) are reading this topic (0 Guests and 0 Anonymous Users)
0 Members:

Topic Options Reply to this topicStart new topicStart Poll

 


:: support us ::




ElectronicsSkin by DutchDork & The-Force