Re: Question about Bandgap reference and BETA of Bipolar dev
Thanks so much Keith!! Thanks Saro too!
I understand your explanations; and I agree with them. The base current (base resistance) will damage the Bandgap performance.
But now I have another doubt:
In standard CMOS process, often (or always), the value of BETA for the PNP devices are low, for instance, 1 or 2. However, I have designed many BGRs using these parasitic BJT and these references worked perfectly. That is, the achieved temperature performance was around 25 ppm/°C – what it is in agreement to the literature. In the most part of IEEE papers, they also present traditional BGRs that work perfectly with parasitic devices with beta equal to 1 or 2.
So my question is: if the base current damages the BGR performance, how is it possible to achieve great temperature coefficient through references using this parasitic device?
Keith:
In another words, if you change the value of the temperature compensation factor (for instance, ratio of the resistors),
Could you correct the curvature of your output voltage (green curve in your simulation) Or is it impossible to correct this curvature?
Thanks for this great discussion.
Added after 8 minutes:
I`m doing this question because it is possible that I did something, in my BGR design that overcame this limitation of low BETA. However, I do not know what I am doing. It is unconscious.
Best Regards,