Hi,

    I want to fix some architecture for a Thermometric DAC.
    I want to add a Δ-Σ Randomizer for selection of Thermometric Current Cells at a given code.
   
    Can someone Indicate Pros vs. Cons for this scheme ??

    What i can think of,
    Advantage -- Distributes & Randomizes Mismatch in Current Cells, thus improving SFDR, SNDR & DNL spikes over the entire range.
    Dis-Advantage -- More Switching in Current Cells. Introduces more Glitches at the Output. Hence, more noise.

How to outweigh one of them ?? Which one will dominate ?? How to determine whether Randomizer will improve or degrade my performance ??

What is the Industry Standard ?? Do people often use Randomizers in their design ?

--
Mayank.

Hopefully, you ae speaking of an oversampling DAC when you propose to use data-directed scrambling etc. I would think that it would be obvious that you don't want data-dependent noise if you are building a Nyquist-rate DAC.

As to checking the effectiveness of your techniques, simulations using MATLAB might be helpful and reasonably fast, although you should only use this to verify static effects such as mismatch. The full spectrum of nonidealities that impact DAC performance cannot be captured like this.

And yes, randomization is used fairly often in DACs to improve SFDR. PRBS-based dithering is quite popular in most cases as the spurs are removed from the entire spectrum, albeit at the cost of a raised noise floor (so if you can afford the higher noise floor). In oversampling DACs, there are various methods used for data-dependent scrambling, although I am not sure if there is any industry standard so to speak.

Vivek

Thanks for your replies.

& Vivek, yes i am talking about Oversampled DACs.

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Could you guys provide me some references on PRBS ??



Quote:
 Dither can be introduced in SDM also along with Randomization. Based on your experiences, you are saying PRBS should give better SFDR than Δ-Σ Randomization/Chopping of current cells as you say. ??