Re: Summing integrator circuit?
From: lemonjuice (exskimos_at_anonymous.to)
Date: 03/14/05
- Next message: Winfield Hill: "Re: Current source design (tricky?)"
- Previous message: Mark Jones: "Re: "white" LED and osc. current source question"
- In reply to: Len Thomas: "Summing integrator circuit?"
- Messages sorted by: [ date ] [ thread ]
Date: 14 Mar 2005 06:33:33 -0800
On Sat, 12 Mar 2005 10:35:33 +1100, Len Thomas <lenthomas102@aol.com>
wrote:
>I know what a summing amp and integrator are as separate circuits, but
>can someone please explain the design criteria for a "summing
>integrator". IOW one op amp doing both tasks.
>
>The integrators I have used in the past have a feedback resistor in
>the MegOhms and cap in parallel. If used with 10K series for each of
>the several summed inputs, this would affect the gain and seemingly
>limit options in this regard.
>
>The frequencies involved are 10-40Hz, subaudio and I am looking for
>unity gain. Input is 6V.
>
>Any suggestions please?
>
>Len
As far as I know an integrator IS one of the many possible Low pass
filters. Compare the transfer functions or frequency response curves of
the 2 and you'll see they are identical.
A resistor put in parallel with the capacitor as someone explained
helps against saturation but it should be noted that it also limits
the integrability of the integrator as its easily shown that
Vout = 1/exp (t/R1*C) * Integral( Vin(t) /R2C) dt) + Vo. Vo is voltage
on capacitor at t=0 ... integration is done between t=0 and a defined
time. R2 is capacitor in parallel with C.
If you use the configuration you mentioned then Fourier transforming
the expression above you'll see that for a unity gain R2 = R1 and for
a cut off frequency fo at 10Hz put fo = 1/2*pi*R2*C.
BTW To get a summing integrator you have to eliminate R and place a
capacitor there. you'd have to add other capacitors to the summing
junction at the Opamp input. Normally they are switched on with FETS .
The advantage of these is mostly in ICs where IC resistors are plagued
by large tolerances , large size and so on. You also get progammability
of the transfer function determined by your FET switch time frequency.
- Next message: Winfield Hill: "Re: Current source design (tricky?)"
- Previous message: Mark Jones: "Re: "white" LED and osc. current source question"
- In reply to: Len Thomas: "Summing integrator circuit?"
- Messages sorted by: [ date ] [ thread ]
Relevant Pages
|
