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Altera_Forum
Honored Contributor I
708 Views

Measuring Power on DE2-70

Hi all, 

 

How can I measure the FPGA core and I/O power on the DE2-70 board (physically or otherwise) while my running my design?
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5 Replies
Altera_Forum
Honored Contributor I
36 Views

 

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How can I measure the FPGA core and I/O power on the DE2-70 board (physically or otherwise) while my running my design? 

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Look at page 23 of the schematic. VCCINT and VCCIO are derived from the main power supplies after going through a couple of resistors. 

 

Replace the existing resistors with appropriate low-valued resistors and then measure the voltage drop over them. 

 

First perform a power analysis of your design using Modelsim to get a VCD file, and then the Quartus power analyzer. Then use that estimate to determine the resistor size. The voltage drop over the resistor need to be small enough to keep the voltages within specification. 

 

Use a pair of scope channels to probe either side of the resistor to measure the small voltage drop. If you have a fancy scope, use the math function to calculate the difference, and then average the difference. Then calculate power. 

 

Cheers, 

Dave
Altera_Forum
Honored Contributor I
36 Views

 

--- Quote Start ---  

 

Replace the existing resistors with appropriate low-valued resistors and then measure the voltage drop over them. 

 

First perform a power analysis of your design using Modelsim to get a VCD file, and then the Quartus power analyzer. Then use that estimate to determine the resistor size. 

--- Quote End ---  

 

 

Thanks Dave. 

 

I was just wondering why would I need to replace the resistors on the board themselves? They are low-valued resistors anyway. Replacing the 0ohm R127 and R128 seem fair but RS1 and RS2?
Altera_Forum
Honored Contributor I
36 Views

 

--- Quote Start ---  

 

I was just wondering why would I need to replace the resistors on the board themselves? 

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The resistors are 0-ohm resistors (the ones that create the VCCIO and VCCINT rails from the main supplies). You can't exactly measure an IR drop, when R = 0, eh? :) 

 

You can't make them too big though, since the VCCINT/IO rail voltage will drop by the amount of the IR drop. So, you want the voltage to be big enough that you can measure it with enough accuracy, but not too big that the FPGA logic stops working correctly. 

 

Cheers, 

Dave
Altera_Forum
Honored Contributor I
36 Views

Yes true it’s not possible to measure a voltage drop across the 0 ohm resistors. But RS1 and RS2 are 10m ohms, these wouldn't need to be replaced if the voltage drop across them is measurable? If the voltage drop across them is too small to be measured accurately couldn't I pass it through an amplifier circuit? 

 

Also would it be safe to say that if I only want to measure the FPGA core power I would only need to measure the voltage across RS1 and RS2? And if I want to measure only FPGA I/O power, I would need to replace the 0 ohm R127 and R128 with a suitable value? 

Altera_Forum
Honored Contributor I
36 Views

 

--- Quote Start ---  

Yes true it’s not possible to measure a voltage drop across the 0 ohm resistors. But RS1 and RS2 are 10m ohms, these wouldn't need to be replaced if the voltage drop across them is measurable? 

 

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I didn't have a copy of the schematic last time I replied. Now I see what you mean; they've got 10 milli-Ohm resistors in the path for VCCINT. 

 

 

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If the voltage drop across them is too small to be measured accurately couldn't I pass it through an amplifier circuit? 

 

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Yes. That's why I suggested using a pair of scope probes, and then use the difference to measure the voltage drop. If you have access to an instrumentation amplifier, then you can measure the voltage drop over the resistor. 

 

 

--- Quote Start ---  

 

Also would it be safe to say that if I only want to measure the FPGA core power I would only need to measure the voltage across RS1 and RS2? And if I want to measure only FPGA I/O power, I would need to replace the 0 ohm R127 and R128 with a suitable value? 

 

--- Quote End ---  

 

 

Yes. 

 

Cheers, 

Dave