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sigma delta adc vs VFC

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garimella

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For dc applications, if inputs are less noisy, would it be better to simply use a VFC instead of ADC? What determines the choice?
 

Hi,

I'm a bit confused.
* in your headline you speak about "delta sigma ADC" but in the text only of "ADC". So is your concern about ADC in general or only "delta sigma ADC"?
* you speak about "simply use VFC". I don't think a VFC solution is more simple than an ADC solution. It is not cheaper either and by far not as linear as a delta sigma ADC.
* then you speak about "better". But "better" without additional information is useless in a technical discussion. Better can be combined with: low cost, linearity, noise, part count, low power, PCB area....and a lot of other..

So I'm a bit lost what answer you expect.

Klaus
 

Suppose my accuracy requirement is .02% ( for 0-10V FSR), would it not be wise to choose VFC. This is because it requires no additional processing except for the gate period and a counter. ADC(sigma delta type) may require additional SPI interface ( assuming for space saving applications), which may in-cur additional hardware logics (in case we wish to implement interface logic in FPGA).
 

.02% linearity isn't easy to achieve with VFC but worse than mainstream performance for SD ADC.
 

Hi FvM, I am surprised when you say VFC cannot offer linearity better than 0.02%. You may please refer to AD650 or AD7741, which offers excellent linearity (and 14 bits resolution)
 

Hi,

AD650 is extremely expensive compared to an ADC.
And for the given linearity you need very good foil capacitors (MKS) and you need to be a very good PCB layout designer.
It by far more difficult than with an ADC.

Processing:
Here I don't see a benefit, either. SPI or I2C is really easy.

Klaus
 

Hi FvM, I am surprised when you say VFC cannot offer linearity better than 0.02%. You may please refer to AD650 or AD7741, which offers excellent linearity (and 14 bits resolution)
Click to expand...
Read answers exactly. I said "not easy to achieve". KlausST mentioned capacitor loss angle as an important reason beyond VFC chip performance. The same problem also affects the linearity of old style integrating ADC, by the way.

I haven't seen VFC for analog signal acquisition in new designs since at least 20 years.
 

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