How to make bipolars matching

How to make bipolars matching

Post by Kuan Zho » Thu, 20 Nov 2003 12:34:39


Hi,
I am designing a circuit which requires the matching of two
identical bipolars. I found a slight mismatch in V(be) will cause
big difference in current. Does anyone know how to solve these problems?
CMOS can use fingers to solve this problem. But bipolar doesn't
have this property.
I am using SiGe 7HP technology from IBM.

Thank you!

sincerely
-------------
Kuan Zhou
ECSE department
 
 
 

How to make bipolars matching

Post by Frank Nits » Thu, 20 Nov 2003 18:36:02

Hi,

if you have multi-emitter bipolar transistors I think you can improve
matching by connecting the multiple emitters from a difference pair
across (e.g. first emitter from transistor 1 with last emitter from
transistor 2 a.s.o.)

Frank.
Technical Manager Chipdesign
MAZeT GmbH, Germany


Kuan Zhou schrieb:

 
 
 

How to make bipolars matching

Post by Hristo Bra » Thu, 20 Nov 2003 21:43:37

You can use the same thing as for the MOS transistors - in this case you
have the area as parameter (or if you don't have it you can always put
several devices in parallel) is if one of the transistors has area A and the
second one has 10*A the current ratio will be 1:10. And no problems with the
matching.

Another possibility is to put resistors in the emitters. In this case the
current ratio will be mainly determined by the resistor ratio.

BR,
Hristo