01-31-2021 10:42 AM
Can you tell me where the temperature sensing diode pins (DXP_0 and DXN_0) are located on Xylinx ZYNC chip ( XC7020) on the CLG400 package?
Is the temperature measured at the pins (where the chip connects to the board) or at the junction inside the chip? I know the relative location is in the center, but I want to know where it is measured locally.
01-31-2021 11:17 AM
As I understand it , the diode is just formed as part of the silicon
its not a separate item
silicon I understand is a good conductor of heat , and high power chips tend to have a heat spreader which further equaliseds the heat
so the diode is a measure of the silicon temperature,
01-31-2021 01:59 PM
Like @drjohnsmith said, the temperature sensing element is almost certainly part of the silicon, usually just a substrate PNP transistor in CMOS technology. It's unlikely to be a diode (i.e. PN junction), as, contrary to common belief, diodes aren't a great temperature sensor (too many inaccuracies). Instead it's usually a diode-connected PNP or NPN transistor, which eliminates a lot of the inaccuracies of a simple PN junction.
So unless someone from Xilinx tells you differently, assume that it's part of the silicon, and not related in any way to the pins. I believe the pins are just there so you can use a more accurate external temperature sensor IC if you want. Xilinx specs for the internal XADC temperature sensor are +/- 6 degrees over -55 to +125, which isn't great. You might get better than +/- 1 degree with an external IC.
02-01-2021 08:20 AM - edited 02-01-2021 08:22 AM
Yes, you can just use the XADC which is part of all Zynq devices. One of the fixed ADC inputs is the temperature sensing element. You can either develop a software application using the xadcps_vX_X drivers without implementing any logic on the FPGA (although the PL section must be powered up, as far as I know), or you can implement the LogicCORE AXI XADC IP block and use the sysmon_vX_X drivers in your software app (my favourite method). You can even view the temperature in the hardware manager in Vivado.
02-01-2021 09:22 AM
i do not think the Zynq ha sits own diode,
The zynq is just part of the silicon I think
so the diode you menton is the sensor to use,
I also think, though some one more knowledgeable on details will be able to say
but the external diode and the internal diode used to measure temperature are either co located or are even the same ,