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corgan
Joined: 15 Jan 2002
Posts: 56
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 20 May 2002 7:33 Analog Power vs Digtal Power |
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Could anyone know what's the definition and difference of "analog power"
and "digital power"??
Thanks in advance!
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joe2moon
Joined: 19 Apr 2002
Posts: 376
Helped: 12
Location: MOON
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| 13 Sep 2002 8:20 Re: Analog Power vs Digtal Power |
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 Analog power is the power(AVDD) for the analog circuit(s) inside your chip, such as PLL(phase lock loop), ADC(analog-to-digital converter), DAC(digital-to-analog converter), ... .etc.
On the other hand, digital power(VDD) is the power for the digital circuit(s) in the chip, usually the CORE.
Because the digital signal(s), especially the clock(s) are usually switching very frequently. In order to reduce the influence (or you may call it "crosstalk" , "electro-magnetic interference(EMI)"), we usually use different power pad for analog & digital blocks.
ps:
Use several power pads in a chip should take the ESD(electro-static discharge) protection between different power pads into consideration.
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kinysh
Joined: 16 Jul 2002
Posts: 67
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| 16 Sep 2002 23:50 |
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For all those power.
can we use the same ground pad?
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gabby
Joined: 18 Mar 2002
Posts: 97
Location: Israel
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| 17 Sep 2002 0:03 |
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Hi Kinysh.
Is not recommended to use the same ground pad.
For best results you must use to separate grounds like gnd(for digital ground)
and agnd(analog ground) and make the connect of them only in one
point , you can use for connect them also a ferrid filter and some caps .
Make sure when you make the pcb to reduce under the analog parts
digital layer of anything like power gnd and signals, and if you can't
also put a layer of analog ground to cross from them and the comp.
Best rerards. 
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CADDevil
Joined: 26 Jun 2001
Posts: 122
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| 17 Sep 2002 0:16 |
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| kinysh wrote: |
For all those power.
can we use the same ground pad? |
Hello,
do not use the same ground pad. Use separate grounds for digital part and for analog part and connect them only in one point, as near to power supply as possible.
If you look at some datasheets from Analog Devices (especially A/D and D/A converters), you can find there the chapter "PCB desing and grounding". Look at this. Also, Analog Devices have some engineering notes about the subject of mixing digital and analog signals.
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okguy
Joined: 01 Mar 2002
Posts: 564
Helped: 6
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| 20 Jan 2003 15:10 |
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If your analog part is very sensitive, you should use 2 separate regulators on your board, to get to separate voltages. If cost allows...
OkGuy
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blankcd
Joined: 21 Mar 2002
Posts: 23
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| 20 Jan 2003 15:23 |
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go to analog device website.
http://www.analog.com
You can find AD9884A Evaluation Kit Schematics.
This AD9884 Schematics will help you.
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