What are your specs about the BANDGAP?

[jake]

1/f noise bandgap

Who can tell me the specs of your BANDGAP, such as, Noise(10-20KHz) and PSRR(<1KHz)?I am doing a BANDGAP with 10uV output noise and 80db PSRR. It's very hard to realize.

 

[tsanlee]

Who much vdd application voltage is used ?

if the VDD olny 1.8v ,the 80B PSRR is not so easily.

if the VDD voltage is more than 2.5v .
the 80dB PSRR is possible, you can reference some paper .


But the Noise 10 uV is so difficult to do it.
The normal Nosie is 20~25uV in standard CMOS process .

I don't know the noise level in BJT or BICMOS process.

 

[jake]

Who much vdd application voltage is used ?

if the VDD olny 1.8v ,the 80B PSRR is not so easily.

if the VDD voltage is more than 2.5v .
the 80dB PSRR is possible, you can reference some paper .


But the Noise 10 uV is so difficult to do it.
The normal Nosie is 20~25uV in standard CMOS process .

I don't know the noise level in BJT or BICMOS process.

yes, The Vdd voltage is 2.7v to 4.0v. The PSRR is realized.
But the Noise is to hard to realize.
And I will realize a 1.6v output voltage reference. The buffer also contributes noise to the output.

 

[fantaci]

What kind of PSRR? DC or AC?

 

[Apollo13]

Do you mean line regulation as DC PSRR?
Or how do you define DC PSRR.
PSRR as far as I know is related to small signal so has to be AC.

 

[jake]

What kind of PSRR? DC or AC?

Of course, It's AC PSRR. And an AC source at the input(VDD), and do an AC analysis, measure it at output.

 

[tsanlee]

The DC PSRR in Bandgap spec. we often call it "Line Regulation " frequency = 0Hz "= DC "

The bandgap output is 1.25~1.3V ,So you need some buffer .
You can reduce the B.W. of buffer circuit ,this can improve you nosie level .

 

[Apollo13]

Hi tsanlee

There is nothing as DC PSRR and no BGR datasheet mentions line regulation as DC PSRR.

Next your BGR output is varving by 50mv under what conditions. Is it line regulation. Or is it temperature related or process variation.

Also the noise source which is majorly low -frequency inherent to the circuit can only be reduced by chopping.

 

[tsanlee]

Yes, Nobody call it DC PSRR ,Low Frequency PSRR effect the line regulation of bandgap.

The best TC of Bandgap is 1.25~1.3V in different procee.

The process varition on one wafer is ± 50mV~±80mV depend on foundary.

The major noise source come from 1/f noise ,and reduce B.W can reduce nosie(thermal noise and some 1/f noise ).

 

[Apollo13]

Are you saying that you could reduce 1/f noise by redicing the BW of the buffer.
I haver not read or heard any technique that could reduce 1/f noise by BW reduction.
The buffer would in your explanation work more like a filter if I understand your explanation right. And no filter exsists that could reduce the thermal or 1/f noise or device level noise.

Line regulation is a DC specification no relation to AC at all. You cannot call it low frequency PSRR. And low frequency PSRR sub HZ frequency range affects the offset of the BGR not line regulation. The units of line regulation are change in output voltage for per unit change in supply voltage not decibles. PSRR tells a ac ripple in the supply after how much atteunation appears at the output

 

[jake]

Are you saying that you could reduce 1/f noise by redicing the BW of the buffer.
I haver not read or heard any technique that could reduce 1/f noise by BW reduction.
The buffer would in your explanation work more like a filter if I understand your explanation right. And no filter exsists that could reduce the thermal or 1/f noise or device level noise.

Line regulation is a DC specification no relation to AC at all. You cannot call it low frequency PSRR. And low frequency PSRR sub HZ frequency range affects the offset of the BGR not line regulation. The units of line regulation are change in output voltage for per unit change in supply voltage not decibles. PSRR tells a ac ripple in the supply after how much atteunation appears at the output

I also have not read or heard any technique which coulde reduce 1/f noise by BW reducthon. Can you give me some paper about it? In fact, It does so!
BTW: for PSRR, I just care for the low frequecy PSRR(<1KHz), so, it's not necessary to differentiate AC and DC PSRR.

 

[tsanlee]

You can read this book "Analog Integrates Circuit Design / David A. Johns ,Ken Martin"

There are some discussion in chapter 4 .

 

[alok_ky]

U can have the specs of the following order :

DC PSRR : -45 dB
AC PSRR : -25dB
Temp. coeff. : 100 ppm/C
Startup time : 20us