How to generate an accurate current on chip?

[purplestar]

Does anybody know about this? I don't need a very accurate current, maybe ±5% is OK.
Thanks !

 

[karesz]

Hi,
All IC/ASIC Design textbooks are writing over several and concrete solutions...
Take & read min. Tieze & Schenk from "old world of discretes & ICs"
K.

 

[prcken]

you can get accurate current by using using the voltage drived from bandgap voltage over an external resistor, you could find it in Allen's book, too

 

[purplestar]

Hi, prcken
I don't want to use the external resistor, pins are expensive for me. I want a total on chip solution. thanks!

Added after 2 minutes:

Hi, karesz
I will read that book ,thanks

 

[kwkam]

It depends on how accurate of your on chip device.

 

[checkmate]

Two ways.
1. Use an external resistor. Vbg/Rext
2. Use trimming with Vbg/Rint. Even so, you will still suffer from tempco of the on0chip resistor.

 

[purplestar]

Hi, checkmate
No third way.....

Added after 59 seconds:

It depends on how accurate of your on chip device.

±5% is enough

 

[prcken]

i dont think you can do that with internal resistors, variation of internal resistors would be more than 30%!
maybe you could only use trimming, maybe you could switched capacitors to realize the resistor, refer to fig 11.22 of Razavi's design of analog CMOS IC book.

 

[purplestar]

i dont think you can do that with internal resistors, variation of internal resistors would be more than 30%!
maybe you could only use trimming, maybe you could switched capacitors to realize the resistor, refer to fig 11.22 of Razavi's design of analog CMOS IC book.

I also don't have reference clock....

 

[karesz]

Hey,
an oscillator to make isnt a problem nowadays_even, as onchip type too...
K.

 

[purplestar]

Hey,
an oscillator to make isnt a problem nowadays_even, as onchip type too...
K.

the problem is how to make an oscillator with accurate frequency, still i need an accurate current...

 

[karesz]

Hi,
Is it not possible for you to use an external clk pls?
Otherwise the semiconductor vendors have on chip solution, I think we can begin at PICs...
Newest "resonator technique" is with MEMs really semiconductor production compatible.
Btw; I dont no if you need it as integrated circuit/ASIC or "only" as a circuit...
K.

 

[love_analog]

If 5% is acceptable but no extra pin is allowed, trimming the internal resistor seems the best way.
The drift after trimming should be typically < 5%