The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> Reference Current Generation
https://designers-guide.org/forum/YaBB.pl?num=1187275406

Message started by Croaker on Aug 16^th, 2007, 7:43am

Title: Reference Current Generation
Post by Croaker on Aug 16^th, 2007, 7:43am

Hi, is there any way to generate a reference current such that the absolute value does not change as components change? Let's say you used a bandgap voltage and a resistor to generate a current...if the resistor value values, so does the current. The goal is to keep the absolute value of the current constant.

Thanks in advance for your brilliant ideas! :)

Title: Re: Reference Current Generation
Post by aaron_do on Aug 16^th, 2007, 8:33am

You can design a bandgap reference with IPTAT and insensitive to resistor variation. Try searching IEEE xplore for IPTAT reference...

Aaron

Title: Re: Reference Current Generation
Post by MonteCarlo on Aug 18^th, 2007, 6:01am

Unfortunately not. Here are a few options to explore:

Resistor trimming.
Use an off chip resistor.
Switched capacitor resistor (depends on frequency and capacitance).

-Monte

Title: Re: Reference Current Generation
Post by sheldon on Aug 18^th, 2007, 3:47pm

Croaker,

One other thought, can you design around the problem at
a higher level of the system? For example, in an integrated
switched-current DAC, you can use the resistor-type for the
reference current generator and the DAC load resistors. Then
the error is reduced to the mismatch between the resistors.
Since the resistors values will track across process, voltage,
and temperature, the overall system looks like it has absolute
accuracy without actually using precision components.

Best Regards,

Sheldon

Title: Re: Reference Current Generation
Post by aaron_do on Aug 18^th, 2007, 7:06pm

So sorry about that.

I went back and read the papers i had read before on CMOS BG references and seems i had understood the papers wrongly. Funny though, my BG reference seemed to be iptat...

Aaron

Title: Re: Reference Current Generation
Post by fehler on Aug 19^th, 2007, 6:57am

For resistor trimming, now we are using a very time cosuming solution, that use test machine and I2C interface to adjust.
Is there any better choice?

MonteCarlo wrote on Aug 18^th, 2007, 6:01am:

Unfortunately not. Here are a few options to explore:

Resistor trimming.
Use an off chip resistor.
Switched capacitor resistor (depends on frequency and capacitance).

-Monte

Title: Re: Reference Current Generation
Post by Croaker on Aug 20^th, 2007, 2:07pm

Thanks for all the replies! :)