AnsweredAssumed Answered

Advanced 'mux' application problem

Question asked by eden-chen2012 on Oct 30, 2012
Latest reply on Jan 2, 2013 by KJBob

Hi All,
There is a problem in my ADAU1701 project. It paining me for several days.Please help me out...
My project is working in selfboot mode. ADC_RES connect to GND by a 18Kohm resistor.
As the hardware schematic attached,there is only 1 signal come to ADC0 & scaling down the same signal

xdB to ADC1. In this way we can improve the SNR and dynamic range.That is why our design like this.
My problem is, I can't find a good way to switch from one ADC to another.
Please allow me to describe my problem in detail.
Let me assume the experiment condition below.
1)Input a sine tone(1KHz) from the hardware input path.
2)When the input level raised to 0dBV,the distortion immediately raise to 1% or higher in ADC0.
But the signal in ADC1 won't distort untill the input level raise to 20dBV.
3)The input signal level is -10dBV(small signal) & 5dBV(big signal). The signal input to hardware

path jump from one to another(-10dBV <--> 5dBV).

If this system switch the signal from one ADC to another automatically,maybe I can get a good

performance result. Right,if I could find a good way to switch them!
I have did experiment.In the end I can't find a best way.
The experiment was.
Please take a look at the Sigma code attached,there are 3 ways to switch the path in the code.
1)Using 'Slew Mux' cell. It is too slow to switch the signal. We can hear a heavy distorted signal

for a short time(about 1 second). That is come from ADC0 before switching to ADC1 complitely when

signal jump from -10dBV to 5dBV.
2)Using 'MX'(no software slew action). This cell can switch immediately,no distored signal come out.
But 'POP' noise come out clearly when switching.
3)Using 'Slew Mux'&'Mux' together. This is the better way till now I found. Please take a look at the

attached code. In this way, there is no distorted signal come out and the 'POP' noise reduce to next

to nothing to my ears. I was very happy that day. A bad feedback from our acoustic engineer the next

morning. The acoustic guy said he heard a very very little 'POP' noise when playing music. We moved a

wave sweeping equipment to do the testing. Too bad, this problem was enlarged in this equipment. I

tried to modify the parameters of RMS Table3,in the pic attached is the best ones in my experiment.
We can't accept the noise.
What can I do? There is a way to solve this problem in SigmaStudio?
Looking forware to your response.
Thank you very much!

By the way,when I use signal detection cell,it doesn't work(no any status indicating from the output

PIN) in the newest version SigmaStudio 3.7.
There is no problem in version 3.6.