That's obvious, isn't it? You've got a 'multiply' solution. You have A, B, want A/B, then connect a multiplier to make X*B, and feed it to the (-) input of an op amp. Put A on (+) input of the op amp. The op amp output, of course, is X :=3D=3D A/B
The PWM approach works when the multiplier is a positive number; how does one handle multiplication by a negative value?
use the identity a 1 ----- = a ( --- ) b b input voltage -> length of PWM pulse
1/carrier voltage -> voltage of PWM pulse.you should howver start with some sample data in a spreadsheet and see if dividing gives results that are useful.
How do you get the reciprocal of a voltage?
If the voltage would between 0.25 and 1 the reciprocal would vary between 4 and 1.
If the pulse has a constant duration, say 1 ms and if the period increases as the voltage decreases with the period =3D the pulse width for full scale then the period is proportional to the reciprocal.
A resistor - capacitor takes longer to charge to some set level at lower voltage. Maybe over a narrow range the RC could be linear enough.
Then only the period needs to be measured to get the reciprocal.
Bret Cahill
Your application would be well-suited for a microprocessor - like a PIC from Microchip. Some of them even come with one or more ADCs. The ADC can handle frequencies up to 20 kHz. Here in South Africa, PICs will cost equivalent to USD5.
I wish I had known about that earlier. Is it possible to do matched filtering with them?
Bret Cahill
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Sorry guys she is still a little buggy, but I'm working on 'er....
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