Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Phase margin of opamp in bandgap reference

Status
Not open for further replies.

shaq

Full Member level 5
Joined
Jul 23, 2005
Messages
312
Helped
14
Reputation
28
Reaction score
4
Trophy points
1,298
Activity points
3,397
Dear all,

Is it important that phase margin of opamp in bandgap reference?

And, I want to know what is the most important of opamp in bandgap reference.

Plz give me more suggestions.

Thanks so much!!!!
 

nuiscet

Member level 2
Joined
Sep 13, 2005
Messages
53
Helped
3
Reputation
6
Reaction score
0
Trophy points
1,286
Activity points
1,684
Phase magin is necessary. Gain is important to ensure that the voltages of the positive and negitive input terminals are equal, too. and other PSRR is also important for the bandgap voltage undepending on the supply voltage, i think.
 

winsonpku

Advanced Member level 4
Joined
Jul 7, 2005
Messages
119
Helped
6
Reputation
12
Reaction score
0
Trophy points
1,296
Activity points
2,351
i don't think phase margin is important for the opamp used in bandgap.
because bandgap is almost a dc circuit and dc gain and offset of the opamp maybe more important.
shaq said:
Dear all,

Is it important that phase margin of opamp in bandgap reference?

And, I want to know what is the most important of opamp in bandgap reference.

Plz give me more suggestions.

Thanks so much!!!!
 

wonbef

Full Member level 3
Joined
Oct 13, 2004
Messages
188
Helped
8
Reputation
16
Reaction score
6
Trophy points
1,298
Location
Nanshan, Shenzhen
Activity points
1,083
i think phase margin is important to stabilize the bandgap reference system.
 

shaq

Full Member level 5
Joined
Jul 23, 2005
Messages
312
Helped
14
Reputation
28
Reaction score
4
Trophy points
1,298
Activity points
3,397
oh my !!!

Someone says phase margin isn't important, the other says important.

Which one is correct?

I'm so confused.
 

jordan76

Full Member level 3
Joined
Mar 25, 2004
Messages
174
Helped
4
Reputation
8
Reaction score
1
Trophy points
1,298
Activity points
1,852
winsonpku said:
i don't think phase margin is important for the opamp used in bandgap.
because bandgap is almost a dc circuit and dc gain and offset of the opamp maybe more important.

Hi

First of all, for all systems with feedback to work properly, they should be stable otherwise you want an oscillator or something like that!

For the case of bandgap, dc gain, offset and PSRR are all very important parameters besides stability concerns.

Hope it helps!

regards,
jordan76
 

shaq

Full Member level 5
Joined
Jul 23, 2005
Messages
312
Helped
14
Reputation
28
Reaction score
4
Trophy points
1,298
Activity points
3,397
jordan76 said:
winsonpku said:
i don't think phase margin is important for the opamp used in bandgap.
because bandgap is almost a dc circuit and dc gain and offset of the opamp maybe more important.

Hi

First of all, for all systems with feedback to work properly, they should be stable otherwise you want an oscillator or something like that!

For the case of bandgap, dc gain, offset and PSRR are all very important parameters besides stability concerns.

Hope it helps!

regards,
jordan76

Thanks for your suggestion!!!
 

jcpu

Full Member level 4
Joined
Dec 17, 2005
Messages
215
Helped
18
Reputation
36
Reaction score
6
Trophy points
1,298
Activity points
2,968
Other than jordan76's suggestions,
allow me to remind that,
input stage matching of this OPamp is
always on top of the list because
this is one donimant factor of output voltage spread.

Have fun
 

shaq

Full Member level 5
Joined
Jul 23, 2005
Messages
312
Helped
14
Reputation
28
Reaction score
4
Trophy points
1,298
Activity points
3,397
Here, I have a little quetion that is how to minimize the vos of opamp in the bandgap reference circuit.
 

iocx

Newbie level 5
Joined
Jun 26, 2006
Messages
10
Helped
1
Reputation
2
Reaction score
0
Trophy points
1,281
Activity points
1,317
Phase margin is an important parameter to opamp. If you don't design well, the opamp will oscillate.AZ can reduce offset voltage.
 

shaq

Full Member level 5
Joined
Jul 23, 2005
Messages
312
Helped
14
Reputation
28
Reaction score
4
Trophy points
1,298
Activity points
3,397
iocx said:
Phase margin is an important parameter to opamp. If you don't design well, the opamp will oscillate.AZ can reduce offset voltage.

Dear iocx,

What is "AZ" ?
 

flushrat

Full Member level 3
Joined
Jan 25, 2005
Messages
180
Helped
23
Reputation
46
Reaction score
8
Trophy points
1,298
Activity points
1,532
Well matching in layout reduce offset
Besides, start up is important
 

hubert008

Member level 1
Joined
May 24, 2006
Messages
38
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,417
For any system, stablity is important, but when you consider it, you must make sure which loop you consider.
 

eng_Semi

Full Member level 6
Joined
May 3, 2005
Messages
325
Helped
37
Reputation
74
Reaction score
6
Trophy points
1,298
Location
Egypt
Activity points
4,111
Don't care with the PM of the opamp BUT take care of the PM of the loop
 

shaq

Full Member level 5
Joined
Jul 23, 2005
Messages
312
Helped
14
Reputation
28
Reaction score
4
Trophy points
1,298
Activity points
3,397
eng_Semi said:
Don't care with the PM of the opamp BUT take care of the PM of the loop

Don't care about the PM but BJT?
 

khaled fayed

Newbie level 3
Joined
Apr 30, 2006
Messages
4
Helped
2
Reputation
4
Reaction score
1
Trophy points
1,283
Activity points
1,301
Hi All

The PM of the OpAmp itself is not so important however the PM of the whole loop should be considered carefully to avoid oscillations. Also the PSRR of the Opamp should be maximized as much as u can to obtain a supply independent BG reference. and when u r supplying RF circuits that are sensitive to noise u should consume larger current in the BG opamp to minimize the output noise. Also the mismatch of the opamp should be minimized as much as u can by layout and circuit considerations.
 

jordan76

Full Member level 3
Joined
Mar 25, 2004
Messages
174
Helped
4
Reputation
8
Reaction score
1
Trophy points
1,298
Activity points
1,852
shaq said:
iocx said:
Phase margin is an important parameter to opamp. If you don't design well, the opamp will oscillate.AZ can reduce offset voltage.

Dear iocx,

What is "AZ" ?

I guess "AZ" means auto-zero technique to eliminate the DC offset voltage.
You may search for more details in ieee journals or google in the web.

regards,
jordan76
 

pseudockb

Member level 5
Joined
Aug 4, 2004
Messages
89
Helped
8
Reputation
16
Reaction score
1
Trophy points
1,288
Activity points
908
Chopper stabilization can also reduce the offset voltage of the opamp.
 

ipsc

Member level 4
Joined
Jun 8, 2006
Messages
74
Helped
7
Reputation
14
Reaction score
4
Trophy points
1,288
Activity points
1,826
shaq said:
Here, I have a little quetion that is how to minimize the vos of opamp in the bandgap reference circuit.

Same techniques that apply to opamp also apply for Bandgap.
Some of them:
1. common centroid layout for input diff-pair
2. Low VDsat for input diff-pair.
3. Sizing of 2nd-stage input TR. & 1st stage load TRs in the ratio of their currents.

Regards
 

winsonpku

Advanced Member level 4
Joined
Jul 7, 2005
Messages
119
Helped
6
Reputation
12
Reaction score
0
Trophy points
1,296
Activity points
2,351
could you explain the second issue in details?
I can't understand low Vdsat can reduce the offest of opamp

ipsc said:
shaq said:
Here, I have a little quetion that is how to minimize the vos of opamp in the bandgap reference circuit.

Same techniques that apply to opamp also apply for Bandgap.
Some of them:
1. common centroid layout for input diff-pair
2. Low VDsat for input diff-pair.
3. Sizing of 2nd-stage input TR. & 1st stage load TRs in the ratio of their currents.

Regards

Added after 3 minutes:

Why large current will reduce the output noise?
khaled fayed said:
Hi All

when u r supplying RF circuits that are sensitive to noise u should consume larger current in the BG opamp to minimize the output noise.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top