Improving Zipper Noise for AD5280

Please share the schematic. 

There are certain application notes or details available here related to zipper noise.

https://www.analog.com/media/en/reference-design-documentation/reference-designs/CN0226.pdf

https://www.analog.com/media/en/technical-documentation/application-notes/AN-1209.pdf

https://www.analog.com/media/en/technical-documentation/data-sheets/AD5290.pdf -- Figure 35

https://www.analog.com/media/en/technical-documentation/data-sheets/AD7376.pdf - Figure 35

Hello, 

Here's the relevant part of the schematic.

thanks, 

G.

What is the issue with single supply option?

I have requested for the block diagram of the schematic to understand where you wants to have the digipot.

Block diagram shown above does not correlate with the schematic as it does not convey the information that you are seeking here.

Hello, 

The block diagram below (I hope it is clear now) represents the part of schematic I'm interested in

the digipot is DC decoupled and is supplied with a dual rail.

I can exploit a window comparator in order to intercept the zero crossing for a jump in the pot wiper: (E.G jumping from 10 to 100!

My other question is about the effect of a continuous modification of the wiper ( e.g ) if the wiper is linked to the ADC's input voltage which is generated by a variable resistor (e.g: Volume control)

Do you believe there's going to be any unwanted perceived noise?

In this case the effect of the wiper's update should be manageable (small steps) because the resistor's voltage variation is continuous, but I imagine there d be some interaction with the I2C activity. 

Is there any best practice I can follow?

thanks

G.

There will be small transition glitch as the wiper position is changed for small steps.

Additionally, there will be digital feedthrough noise due to activity on the I2C bus. 

You can check the figures 52, 53 in the datasheet. Both are shown for the worst case conditions.

You can add an appropriate low pass or high pass or bandpass filter at the output stage if that is not tolerable in your system.

Thank you!!!

Other question: I am exploiting the AD5280 because of the I2C interface and because it is low cost; unfortunately this device does not implement the SYNC function as in AD5291.

This means that, in order to get rid of any bumps during abrupt changes in the wiper configuration, I  can mimic the SYNC function by means of SHDN pin. 

My idea is to sync the SHDN pin with the signal's zero crossing event.

The sequence would be as follow:

1. Assert SHDN at the first zero crossing 

2. Program the wiper with SHDN asserted

2. Deassert SHDN at the next zero-crossing event after the register program.

The delay would be reasonable and I would get the same effect of the AD5291's SYNC with a less expensive I2C device.

Do you believe this solution can work?

Bear in mind that this condition will be very frequent, so I need to be sure that the device can be frequently put in shutdown.

Thanks for your valuable support, 

Regards

G.

I do not think that is the right step in using SHDN to mimic as SYNC.

A SHDN assertion will connect W-B terminals and open A terminal making it behave like a rheostat. This will create large steps in the output stage.

Yes, W should be grounded, so no output available,  while A would be opened.

The connection of A to the circuit would happen when the signal crosses zero, so I expect an overall improvement.

What do you suggest in alternative considering the  AD5291 as last option?

Does that mean that you want to keep only the +ve signal through digipot and clip the negative signal.

If yes, I do not see any issue in that case.

I can accept to silence the digipot's out  right before an  abrupt transition, update the wiper and then enabling the output ireleasing the wiper to the new value right in the very istant in which the signal crosses zero.

This is compatible with shorting W and B. 

I expect this solution almost bump free... 

does that make sense?

I do not see any issues in this. 

Great! thank you. 

Great! thank you.