CMOS diode connected transistor

Hello guys. I am currently having a research about rectifier for 2.4 GHz Freq (Wi-Fi), my goal is to have a higher PCE (Power Conversion Efficiency), one of its problem is the Vth and the Leakage current of the circuit. now i have red that CMOS diode connected transistor can be a solution to this problem. Do you guys have any idea how to design a good CMOS diode connected transistor based on its W/L?

bwarlord01 said:

... any idea how to design a good CMOS diode connected transistor based on its W/L?

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Connect gate to drain. Valid for any W/L ratio.

i think u are referring to the NMOS diode, i am talking about CMOS diode

erikl said:

Connect gate to drain. Valid for any W/L ratio.

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That's valid for both types of CMOS: NMOS & PMOS ;-)

What voltage/power level do want to rectify?

crutschow said:

What voltage/power level do want to rectify?

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Voltage input level at 0.25 volts

You need more than W/L, at 0.25V crest voltage you need
a low- or zero-VT device - or a charge pump and synchronous
rectifiers, eliminating all forward drop.

Take a look at what RFID people go through, to get tag power.

dick_freebird said:

You need more than W/L, at 0.25V crest voltage you need
a low- or zero-VT device - or a charge pump and synchronous
rectifiers, eliminating all forward drop.

Take a look at what RFID people go through, to get tag power.

Click to expand...

yes, absolutely right! i am using a low voltage threshold transistor. and i am wondering what W/L ratio should i choose to make my output or power efficiency good.

You're in a foot-race between forward losses ("diode" Vf*If) and
reverse losses ("diode" low-Vgs / reverse Vgs leakage). With so
small a max voltage you can expect not-good forward losses.
With some modern technologies, GIDL phenomena can make a
negative Vgs raise the leakage floor as you go more negative
and this is worsened by the same short channel that you'd want
for best forward operation.

I'd approach this as a "sweet spot search" (optimization) with
as much realism regarding the true nature of source and load
as you can wrap around the "energy harvesting core". As one
point, with a discharged load you may find that the "antenna"
fails to make the purported 0.25V, even, when the load is
"seen" through the "rectifier". This can lead to startup issues.
You may need to do things like "UVLO" functions that detach
the load from the charge reservoir until adequately pumped up.

The trade between wide (for forward efficiency) or narrow (for
leak-back efficiency) depends a lot on load and source "box".

If you can (say) make a rung-up tank circuit to drive a higher
VT gate to better "on" and "off" positions, that can beat a fixed
diode bridge. However making this work at 2.4GHz would probably
add more commutation losses than you might stand to gain -
another thing that wants analysis, to say.