Asynchronous I2S FIFO project, an ultimate weapon to fight the jitter

[iancanada]

Originally Posted by qusp

you need to be more specific, quoting a random new years greeting made by someone else is not giving very good context for your question. for example the LFCSP package of the ADP151 has pin 4 as the enable pin.

but i'm not sure which ADP151 you are referring to. also I believe Ian allowed for the alternative use of TPS series regs on some boards

Thanks qusp .

Originally Posted by roender

Hi Ian,

Why are you putting .1uF ceramic capacitor between an unconnected (pin4) pin of ADP151 and ground?

Kind regards,
Mihai

qusp gave correct answer. That cap was reserved for other LDOs such as TPS79333 or TPS79933 . Just keep it open for ADP151.

Rember? my boss may change his mind on BOM at last minute .

Ian

[iancanada]

Originally Posted by 1audio

At this performance level the options for measuring jitter are limited. You can spend a bundle on one of the fancy measuring systems and that makes sense if you need to measure a variety of different sources. However for specific sources you can get very good results using a reference oscillator and a double balanced mixer. If you need to go well below the noise of your reference oscillator there are techniques using two reference oscillators and correlation to extract the phase noise that is common. More here: Techniques for Measuring Phase Noise . Phase noise above the sample rate won't affect the output because its conversion is above the system bandpass. This makes it harder to convert from the cycle to cycle measurements (with an effective bandwidth of 1/2 the sample rate I think) to the final audio output.

You can get a Wavecrest with a 2 pS noise floor, and for less that $700. But it still won't tell you what you want to know as well as either the above method or looking at the output of the dac, which is what matters. Looking at the raw clock is a good analytic tool for seeing how much it has been degraded. The phase noise measurements are the best way to make the measurements.

Main Page has added the ability to make the cross correlation measurement using a sound card. You still need two reference oscillators and double balanced mixers. You can get a noise floor of -170 dBC with care. The minicircuits mixers are certainly good enough to start with. The Crystek oscillators may be good enough but you really need a voltage control input to phase lock the oscillators.

Thanks Demian,

I know there is limitation measuring jitter in time domain. But it would be much more difficult in frequency domain. I'll go through the link to see if I could. BTW, do you have any recommendation on mixers for this kind of audio f XO measurement?

Regards,

Ian

[andrea_mori]

a double balanced mixer like this
WJ WATKINS JOHNSON RF Mixer M1A DC-1000 MHz 7dBm SMA | eBay
an audio spectrum analyzer
a low noise preamplifier like in the Wenzel document (not be necessary if the analyzer noise floor is sufficiently low)
a reference oscillator (like the HCD661 OCXO)

[iancanada]

Originally Posted by Nazar_lv

Hi Ian!
First you measures period jitter not phase, correct you post.
To measure with better accuracy and lower minimum jitter values with you lecroy osc (because of not perfect timing for interliving adc, amplitude-time distirtion conversion etc.) you need to
1. Apply ERES (3bit) function
2. Apply SinX interpolation before eres function if you sampling rate is lower than 4Gs
3. You signal must have maximim amplitude, just before clipping of ADC, use variable attenuator of you scope to maximize signal level.
4. Rise time of you signal should be 3-4ns for lowest osc jitter

regards, Nazar

Thanks Nazar for finding my typing mistake, already have them corrected.

1. Apply ERES (3bit) function -- could you give a bit more details?

2. Apply SinX interpolation before eres function if you sampling rate is lower than 4Gs -- mine already at 8GS/s

3. You signal must have maximim amplitude, just before clipping of ADC, use variable attenuator of you scope to maximize signal level. --- Yes it is, you are right. Did this way

4. Rise time of you signal should be 3-4ns for lowest osc jitter -- Now is around 0.9ns, too small?

Originally Posted by Nazar_lv

What you need for more accuracy with you scope i describe in previous post. High bandwidth is not needed for jitter measurement (for audio equipment) at all.

PS And wm8804 MCLK output not designet to work on 50ohm load.

I think you mean rise time of a scope is more important than the bandwidth on jitter measurement. But usually those two numbers are linked. Have you ever try the result reducing the bandwidth from 1GHz to 200MHz for a same jitter measurment?

I'm not happy with the WM8805 result. That result was measured after I powered it by a battery. It was even worse when I use ac power. Do your mean the MCLK driver of the WM8805 is not good enough? What is the most optimized output impedance it was designed to drive into? I have a 1.8pf active probe, I can measure the 8805 output without load.

I attached the docs of jitter measure package I'm using right now. Please let me know for any suggestion on my jitter testing. Just hope there still be some space to get improve.

Regards,

Ian

[ed linssen]

Originally Posted by iancanada

1, If you don't use the spdif output function for
2, Replace the dual xo clock board with the standard single clock board and play 44.1K, to see if everything is OK.

Good luck

Ian

Hi Ian,

Thanks for your advice of checking!
I can use all inputs, normaly spoken, with a terrific good SQ. So playing music does not give any problem. It is my missing of the possibility to record from the Fifo....
With the single board and 44.1 khz, using the WaveIO via backdoor, output sends rather continuous static, about max level.
These are the findings so far.
!!!!
I must add, that the static ticks occur continuously at the (coax)output even when no input is connected to the SPIDF board , not even the backdoor!
Ed

[ed linssen]

Originally Posted by bigpandahk

I had the same problem before, did you short one of the pin to ground (R24 if my memory correct)? this was the step I did not realize and caused no output.

Yes, this step was and is still not very clear to me to. I remember I questionned it it the forum.
What I did, I used a small piece of wire to short pin4 to the nearby groundplane, while connecting it to the signaltrack as well. I am though not shure I did the right thing here. Maybe I should try and cut that wire and see(hear) what happens.
Ed

[iancanada]

Originally Posted by ed linssen

Hi Ian,

Thanks for your advice of checking!
I can use all inputs, normaly spoken, with a terrific good SQ. So playing music does not give any problem. It is my missing of the possibility to record from the Fifo....
With the single board and 44.1 khz, using the WaveIO via backdoor, output sends rather continuous static, about max level.
These are the findings so far.
!!!!
I must add, that the static ticks occur continuously at the (coax)output even when no input is connected to the SPIDF board , not even the backdoor!
Ed

Sorry, still did get your problem. You mean the coaxial output of the s/pdif board has problem?

Ian

[qusp]

Ian, I believe Demian was recommending the minicircuits frequency mixers

[ed linssen]

Originally Posted by iancanada

Sorry, still did get your problem. You mean the coaxial output of the s/pdif board has problem?

Ian

Yes, Ian. I don't get output from the (BNC chassispart) output on the S/PDIF board. Just static.
Thanks for your suggestions.
Ed

[ed linssen]

Originally Posted by bigpandahk

I had the same problem before, did you short one of the pin to ground (R24 if my memory correct)? this was the step I did not realize and caused no output.

Hi Ian/Bigpandahk

Not succesfull until now. I took the backdoor-connector from the board to check it. Found no problem and reconnected it. In the picture I show you how I did that. It is the manual from Ian himself. I show you how I bridged the ground- and the signalpads on the R22 position.
Ed