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7th January 2017, 23:54 #1
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Integrator for dual slope ADC
Hello,
I have designed an integrator with 15 M resistance and 40 PF. The input is a single pulse with a width of 409Us and higher value is 700 mv and lower value is 100mv. The deintegration curve is exponential. How to make it linear?

7th January 2017, 23:54

8th January 2017, 10:07 #2
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Re: Integrator for dual slope ADC
The deintegration curve is exponential. How to make it linear?

8th January 2017, 18:29 #3
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Re: Integrator for dual slope ADC
To make the discharge curve linear you need a circuit to generate a constant current such as a current mirror.
Here's another article of interest.Zapper
Curmudgeon Elektroniker
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9th January 2017, 13:16 #4
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Re: Integrator for dual slope ADC
Hello,
Can you please elaborate a little constant current source should be added where in the circuit?

9th January 2017, 13:16

9th January 2017, 13:21 #5
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Re: Integrator for dual slope ADC
Can you please elaborate a little constant current source should be added where in the circuit?
The commonly used dual slope ADC circuit (as in the above linked Wikipedia article) is based on an active integrator and won't need a current source, just switches the reference voltage to the integrator.

9th January 2017, 14:55 #6
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9th January 2017, 14:55

9th January 2017, 15:00 #7
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Re: Integrator for dual slope ADC
I'm unable to recognize a dualslope topology in your schematic. It looks more like single slope.

9th January 2017, 16:30 #8
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Re: Integrator for dual slope ADC
It is a dual slope topology instead of the control circuit I have given a PWL input. Integration time is 409 Us. I am initially doing the simulation for only one period as I will design the digital part later on.

9th January 2017, 17:00 #9
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Re: Integrator for dual slope ADC
O.K. we can't see the waveforms. To achieve correct integrator behavior, there should be no resistor R1 permantly connected parallel to the integration capacitor.

9th January 2017, 17:00

9th January 2017, 18:47 #10
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9th January 2017, 18:55 #11
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9th January 2017, 19:46 #12
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Re: Integrator for dual slope ADC
You might need a reset switch in place of the resistor.

9th January 2017, 22:51 #13
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Re: Integrator for dual slope ADC

10th January 2017, 08:59 #14
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Re: Integrator for dual slope ADC
In principle, a dualslope circuit doesn't need a reset switch if it performs integration and deintegration phase alternatingly. Deintegration would stop when the integrator output voltage is exactly zero.
Practical dualslope circuits implement an additional reset or autozero phase after deintegration. In this phase, a reset switch or equivalent reset circuit removes residual integrator charge and provides clean initial conditions for the succeeding integrator phase.
It seems to me that you are more guessing about dualslope operation than clearly understanding the principle. You may get more clarity by studying existing dualslope ADC implementations, e.g. ICs like Intersil ICL7106 or Microchip TC500.
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