Bandgap的温度系数与输出电压

analogworld · 发表于 2011-10-1 23:34:09

马上注册，结交更多好友，享用更多功能，让你轻松玩转社区。

您需要登录才可以下载或查看，没有账号？注册

x

Bandgap的设计原理公示为： Vref=Vbe+KVtlnn. 这样可以有Vbe的温度系数来确定Klnn的值，那么vref=?呢？如果需要design一个vref输出1.25V，那么是否会对Klnn有影响呢？
不知道设计时一般按照什么样的流程来做，如何折衷呢，如果输出电压有要求时，是否就无法实现0温度系数？谢谢！

naoz · 发表于 2011-10-2 01:53:09

本帖最后由 naoz 于 2011-10-2 01:54 编辑

bandgap可以实现一个1.2V左右的ref
通常的办法是实现一个PTAT项 Vref =A * Vbe +B * Delta Vbe/R

设计的时候一般先选结构，根据工艺，是CMOS还是BiCMOS，根据应用，是Low voltage的还是正常的，根据功耗等
然后根据公式，调整关键电阻的值，把温度系数调到最小
如果仅仅是一阶补偿的话就是一个抛物线啦高阶补偿的话可以做一些曲率

关于其他的ref的话用运放抬一抬不就行了。。。

ps lz入行几年了？感觉基础知识还是不够扎实啊，莫生气，只是感觉。

Chilton · 发表于 2011-10-2 05:29:54

Vref is the resultant of the a positive tempco voltage (multiple delta_Vt's) and a negative tempco voltage (Vbe). Each process/device has its own device characteristic therefore the sweet zero tempco spot is slightly different from process to process, although they all fall within the 1.25v range.

BTW, bandgap circuit has no relation with silicon bandgap. It just happens to be so in the 1.25 voltage range. You can scale it down to any voltage if you chose current summation instead of voltage summation.

kmchen3089 · 发表于 2011-10-2 10:48:11

if you design opamp based bandgap ckt(which is that there
is one opamp ckt in the ptat ckt(propotional to absolute temperature ckt)
then you must care about the dc offset voltage(input systematic offset voltage
and input random device mismatch voltage)of the opamp you used
because the bandgap voltage
accuracy will be strongly affected by the dc offset voltage of the opamp(see Razavi's
analog ckt design text book Fig 11.12 (bandgap ckt chapter)
if you increase opamp open loop dc gain then it will decrease
input systematic offset voltage;if you choose very large device size for input
differential pair for the opamp and layout style is common centroid
then it will decrease input random device mismatch voltage