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Clock Repeater IC, Jitter correction ic, clock distibution
Clock Repeater IC, Jitter correction ic, clock distibution
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Old 5th March 2019, 02:21 AM   #1
JayShoe is offline JayShoe  United States
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Join Date: Oct 2011
Clock Repeater IC, Jitter correction ic, clock distibution
Default Clock Repeater IC, Jitter correction ic, clock distibution

Hello diyaudio,

Let's say you had a DSP with a master clock. You have a TDM8 configuration (i2s). You have 4 DAC's on different PCB's and you need to feed that clock signal to all 4 DAC's over 6 inch ribbon cables. What's the right way to split up the master clock signal to each DAC separately while maintaining accuracy? Is there a particular master clock Repeater IC?

Jay
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Old 5th March 2019, 02:47 AM   #2
JayShoe is offline JayShoe  United States
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Join Date: Oct 2011
Clock Repeater IC, Jitter correction ic, clock distibution
I'm starting to answer my own question.

Quote:
MCLK distribution
All main-boards and slave boards need to be synchronous to a common master clock (MCLK). Therefore future freeDSP main-boards must feature a MCLK distribution circuit, which provides several synchronous but independant MCLK outputs. These will supply a MCLK to the onboard DSP and also to each expansion board via the standard freeDSP expansion connector.

freeDSP main-boards provide MCLK: 24.576 MHz
freeDSPx expansions receive MCLK via standard freeDSP expansion connector
I'll start looking at the freedsp boards for examples.
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Old 5th March 2019, 06:04 AM   #3
Markw4 is offline Markw4  United States
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If you want a basic clock buffer and distributor, you might look at NB3L553. If you want to regenerate a clock and produce output with very low jitter then LTC6952 is very sophisticated part. It can also be used, among other things, for synthesizing a new clock frequency at some a/b ratio relative to a reference clock, where 'a' and 'b' are integers. Not cheap though.
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Old 5th March 2019, 12:05 PM   #4
JayShoe is offline JayShoe  United States
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Join Date: Oct 2011
Clock Repeater IC, Jitter correction ic, clock distibution
Hello Markw4,

Quote:
If you want a basic clock buffer and distributor, you might look at NB3L553. If you want to regenerate a clock and produce output with very low jitter then LTC6952 is very sophisticated part. It can also be used, among other things, for synthesizing a new clock frequency at some a/b ratio relative to a reference clock, where 'a' and 'b' are integers. Not cheap though.
Thanks! That's very helpful.

freeDSP-CLASSIC-SMD-B-master uses IDT2305NZ like this.

Clock Repeater IC, Jitter correction ic, clock distibution-freedsp-classic-smd-master-clock-png

freeDSP-ALLinONE uses IDT2309NZ like this.

Clock Repeater IC, Jitter correction ic, clock distibution-freedsp-allinone-clock-png

freeDSP-aurora seems to be using the NC7SZ157... Like this. Although the datasheet is very technical and I'm not positive what this is doing. :-P In fact, I'm not sure that it's distributing the clock as much as just maybe strengthening it?

Clock Repeater IC, Jitter correction ic, clock distibution-freedsp-aurora-clock-png


I'll probably just follow the lead from the freeDSP-CLASSIC-SMD-B for my project. Or I'll look into the NB3L553. Seems simple.
Attached Images
File Type: png freeDSP-aurora-clock.png (9.3 KB, 403 views)
File Type: png freeDSP-ALLinONE-clock.png (23.6 KB, 402 views)
File Type: png freeDSP-CLASSIC-SMD-B-master-clock.png (17.6 KB, 210 views)
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Old 5th March 2019, 12:43 PM   #5
Markw4 is offline Markw4  United States
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It is providing multiple copies of the clock that can go to different parts of the circuitry. In that case, its often good to have low skew (the timing difference between the different clock copy outputs) and low jitter from various noise sources including power supply noise due to all the output channels switching at once, and whatever other noise may be on the power pins of the clock buffer.
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Old 5th March 2019, 08:02 PM   #6
wealas is offline wealas
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You could also get Ian's McDualXO board that has everything but the ribbon cable (it uses coax cables).
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Old 5th March 2019, 08:24 PM   #7
TNT is offline TNT  Sweden
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Problems in your Kickstarter adventure?

//
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More distortion to the people!
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Old 5th March 2019, 08:42 PM   #8
JayShoe is offline JayShoe  United States
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Join Date: Oct 2011
Clock Repeater IC, Jitter correction ic, clock distibution
Quote:
Problems in your Kickstarter adventure?
Lol, I'm still eagerly waiting for the Aurora. But ultimately may redesign it without it's ADC/DAC parts so I can connect add-on boards instead. Or may possibly continue to research the Teensy Bridge I've been working on. So I might need to distribute some clocks! :-)
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Old 6th March 2019, 04:40 AM   #9
JayShoe is offline JayShoe  United States
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Clock Repeater IC, Jitter correction ic, clock distibution
I just realized something. I know when going from board to multiple boards it's a good idea to have clock distribution. But what about one board with multiple DAC/ADC parts. Is it ok to have 2 DAC's on one mclk source? 3 DAC's? I just realized that I might need clock distribution on each add-on board in addition to the main board because each add-on board will have multiple ADC/da parts. Any input is appreciated!
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Old 6th March 2019, 12:39 PM   #10
Markw4 is offline Markw4  United States
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Transporting clock signals between boards without picking up a likely significant amount of jitter would seem to require some careful thought and engineering. Ribbon cables are not as good as more rigid connections. Use quality gold-flashed or gold plated connectors, use ground pins (and wires for any cables) adjacent to clock signals on both sides for improve signal integrity. Perhaps better to convert LVCMOS signals to LVDS or LVPECL for transport across multiple boards. The signals can be converted back to LVCMOS when and where needed. Otherwise, 'clock cleaner' chips and or techniques can be used to help clean up clock signals. When using additional chips such as LVDS <> LVCMOS converters and or clock cleaners/regenerators it might be good to look at the added jitter they may cause down at 10Hz offset. Many devices have impressive jitter numbers specified at 12kHz offset, which is meaningless for audio.
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