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Message started by niloun on Aug 9th, 2017, 12:25am

Title: SAR ADC Power Consumption
Post by niloun on Aug 9th, 2017, 12:25am

Hello everyone,

I need to simulate the power consumption of an SAR ADC to compare it with other existing SAR ADCs. Should I simulate the dynamic power for just one bit conversion, or just one sample (any specific input? e.g Vmid), or the whole period of a sine wave?

Basically, what is the standard way of reporting the power consumption of an SAR ADC?

Thank you,

Title: Re: SAR ADC Power Consumption
Post by DanielLam on Aug 9th, 2017, 4:20pm


I'll try to help by making a few points. There isn't really a standard way of reporting power. People will just state what is included in their power measurements, and you have to filter those results to compare ADCs.

1) It is usually tricky to compare power against other SAR ADCs because you it might be hard to figure out what is included and not included. For example, some papers do not include input buffer or reference buffer power, which could be higher than the ADC power itself. Another example might be an ADC with digital calibration, and the big DSP power is not included. To add onto this, some chips might have such a big bypass capacitor on-chip such that they do not require reference buffers. So their design would consume less power, but takes a ton of area.

2) Higher sampling frequency and higher resolution ADCs typically use more power. So you might try to compare using a figure-of-merit (FOM). If the ADCs are distortion limited, use the Walden. If the ADCs are noise limited, use the Schreier. The cutoff point is about 10 ENOB, but you can calculate both and see.

3) There has been extensive work comparing the switching energy of different SAR ADCs. I think these are fair comparisons in terms of DAC swtching power. Although, in some switching schemes you may need Vref and Vcm, and require two reference buffers instead of one. So the power calculation can get tricky here as well.

4) If you want a rough estimate, go through all the digital codes (full sine wave) and average. If possible, include reference and input buffer power. Also, use extracted layouts if you have them.

5) Different codes will use different amounts of energy. So you cannot just use one bit conversion or one sample.

Title: Re: SAR ADC Power Consumption
Post by niloun on Aug 10th, 2017, 12:30am

Thanks so much for the perfect answer. So to measure the total dynamic power consumption I clip supply current (including currents from every block in the SAR ADC) for one period of the input sine wave (from the first sample to the last bit of last sample) and take an average of it then multiply the result with supply voltage value, I do the same for Vcm.

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