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Brad Albing

Very Low Gate Threshold FET – Maybe Too Low?

Brad Albing
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RedDerek
RedDerek
7/3/2013 1:57:11 PM
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Master
FET mirror
I will need to look at the data sheet. I see some interesting applications as well. As for construction, it looks to be that middle-of-the-road device between the enhancement and depletion MOSFET. I looked years ago about using MOSFETs as a current mirror, but matching two devices would be very difficult, obviously I would not be looking at a 0 Vgs device then. But to match, the best method, as shown, is to co-package. This way the semi manfucturer can grab adjacent die off the wafer to help ensure the match. MOSFET characteristics will shift from lot to lot, and from wafer to wafer within the same lot. And there is even a shift from one side of the wafer to the other. But if one can get die that are located next to eachother on the wafer, one is sure to get a matched pair.

The space program that needed good current mirrors would pay a premium for number sequenced BJT devices so that they know that part xxxx and part xxxx±1 will match each other. Just not sure how they knew when the next sequenced number means the start of a new row of parts on the wafer.

Oh, as for application, I can see this would be great for driving LED strings. With matched FETs, the focus would be Rds*Id loss, yet be able to have one string have the same current as the next. Trick is that if one has multiple strings, say 4 and 5 or more, the 2 FET package would not be much help - I would look at a quad-packed part; but the Vth would be higher compared to this one.

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amrutah
amrutah
6/30/2013 11:54:54 PM
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Re: always on circuits
SunitaT,

   In case of CMOS circuits. then you will have to build negative charge pumps t generate the negative supply and then use them to bias these devices. Negative charge pumps are a monster in themselves to handle...

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SunitaT0
SunitaT0
6/30/2013 11:18:12 PM
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Master
Re: always on circuits
But the critical factor is we are on the verge of 0 volts and to turn off we need to go below 0V.

@amrutah, yes I agree with you. Switching off the FET by giving voltage which is less than 0V is critical. Is it better to have device which require negative voltage to switch off or is it preferrable to have device which turns on when we give +ve voltage ?

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Brad Albing
Brad Albing
6/30/2013 10:07:57 PM
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Blogger
Re: always on circuits
@amrutah - exactly my point - it's helpful to have a device with very low turn-on threshold - but not too low, or you'll need a negative voltage to insure it's turned-off. So it starts to look like a depletion mode part. Still, I'm glad to see someone is making these devices.

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amrutah
amrutah
6/30/2013 7:23:57 PM
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Master
Re: always on circuits
SunitaT,

   I have read papers where there are twin well process and low voltage to support, there are designs where the circuit can operate at low as 0.3V ( for 45nm process nodes). Check this

 But the critical factor is we are on the verge of 0 volts and to turn off we need to go below 0V.

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SunitaT0
SunitaT0
6/30/2013 6:19:50 PM
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Master
Re: always on circuits
These devices can be used in series (or cascode) with High Vt device used for power gating to reduce leakage during off period.


@amrutah, interesting idea. I agree with your suggestion putting this device which has high leakage in series with thigh Vt device definitely helps us to reduce leakage during off period. I am curious to know if such architecture is commonly preferred in the designs ?

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SunitaT0
SunitaT0
6/30/2013 6:02:18 PM
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Master
Re : Very Low Gate Threshold FET Maybe Too Low?
@Brad, thanks for the post. Interesting to learn about FET which is neither  enhancement mode FET nor depletion mode FET. Eagerly looking forward for outcome of your research on this product.

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Brad Albing
Brad Albing
6/30/2013 5:30:29 PM
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Blogger
Re: Switching
I think it does indeed lend itself to use in battery operated devices. Lots of possibilities here.

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Brad Albing
Brad Albing
6/30/2013 5:28:17 PM
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Re: device construction
I do have access to more info - let me see if I can get one of the AMD guys to comment. Stand by.

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Maciel
Maciel
6/30/2013 4:32:12 PM
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Newbie
Switching
Due to inrush current of this device is very low, we can use in drive applications, mainly for switching circuits powered by batteries.

What do you think?

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