A very good ADC for the future ?
Hi @Roby, the QA402 is a solid architecture for future converter experiments and is used for a lot of converter evaluations. The change isn’t so much just dropping in another converter–there are a lot of things that come with the converter change that are required to get the expected performance and that includes the attenuation network, the variable gain stage design, the protection circuitry. Usually, and this is true in the case of the converters from ESS and AKM and Cirrus, they provide a simple input (or output) reference schematic that let’s them achieve their performance metrics. But the utility of the circuits is low. For example, this is in the sample input circuit of the AK5397 that lets them meet the published spec:
This circuit as shown is of limited utility. Note the input impedance is 1k (~500 ohms in single-ended mode!) and it has a lot of attenuation (which makes things a bit easier than a lot of gain). There is no attenuator, there are no other gain ranges, and there is no input protection. The challenge comes from an input stage with 100k impedance that is protected from overload, handling multiple gain stages, etc.
Some boards have been built with ES9822 and other converters, and I agree the ESS stuff is nice but whatever the final direction, a next product will be some time away (and is made worse by the silicon shortage).
I added this graph to my post on the silicon shortage issue here. This plot shows the % of TI DCDC converters at Digikey that are in stock. And every day it is getting worse. What this shows is that in early June about 60% of Digikey’s “normally stocked products” were in stock. And at the beginning of July, that had fallen to 54%. The exact numbers are unimportant–it’s the trend. And currently we are watching worldwide suppliers selling out of stock and not getting it replenished. This is very serious. Now, presumably TI is still making parts at their current rate of 2019 (and likely a good bit higher). So it’s the world wide demand that is soaking things up.
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