| Author |
Message |
starrinesss
Joined: 19 Jun 2007
Posts: 21
Location: China
|
 18 Jan 2008 3:28 Re: Bandgap Reference |
|
|
|
| firsttimedesigning wrote: |
| yeah but when i fabricate the chip, the resistance will vary within 20%...a 4k resistor might only have 3.2k resistance. the result wont be very accurate...i need something that can generate a very accurate bias voltage...something that only have error within 0.1%... |
It depends the match of 2 resistors, if there is a kind of res with less than 1% mismatch that have the same geometrical size, that will fit your design.
And you'd better use large W the res
|
|
| Back to top |
|
 |
vbhupendra
Joined: 11 May 2005
Posts: 241
Helped: 6
Location: GOA, INDIA
|
| 21 Jan 2008 7:52 Re: Bandgap Reference |
|
|
|
| you can use techniques shown in allen holberg or razavi to get voltage ref higher than bg.
|
|
| Back to top |
|
|
joezl82
Joined: 05 Nov 2005
Posts: 12
|
| 22 Jan 2008 14:55 Bandgap Reference |
|
|
|
prefer use gand gap
ldo in not suit in this application
|
|
| Back to top |
|
|
mahgoub
Joined: 26 Oct 2007
Posts: 96
Helped: 2
|
| 22 Jan 2008 22:59 Re: Bandgap Reference |
|
|
|
| i dont understand if he is not going to use bandreference how is the voltages are referenced to it
|
|
| Back to top |
|
|
peni
Joined: 20 Jan 2008
Posts: 65
Helped: 4
|
| 24 Jan 2008 17:25 Re: Bandgap Reference |
|
|
|
| use Bandgap generate fixed voltage , than use LDO to generate higher voltage you want
|
|
| Back to top |
|
|
lijianheng
Joined: 29 Sep 2006
Posts: 133
Helped: 10
|
| 29 Jan 2008 3:52 Re: Bandgap Reference |
|
|
|
Try this one
|
|
| Back to top |
|
|
mydreamhouse
Joined: 07 Oct 2005
Posts: 128
Helped: 3
|
| 29 Jan 2008 19:04 Re: Bandgap Reference |
|
|
|
| you can use LDO or some regulator
|
|
| Back to top |
|
|
engronger
Joined: 19 Feb 2006
Posts: 35
Helped: 1
|
| 31 Jan 2008 4:04 Re: Bandgap Reference |
|
|
|
you amp need a so accurate bias?, usually, what a amp really need is a bias current and some times a reference input voltage, if you need a bias current , you can use a bandgap, and then a current mirror is used to give the bias.
if you need a reference input voltage, and it must be large than 1.2V, you can also use a bandgap, you can read more paper, there are some circuit can give you >1.2V & <1.2V . LDO is not a choice can be choosed. LDO is not used to give a bias ,it is used to give a power supply to core chip.
if you need a bias to some other gate, maybe a rough bias is ok. you can use MOS and resistor to create it .
| firsttimedesigning wrote: |
| So I am trying generate the bias voltage of an op-amp. So far the only circuit I know that can be used to generate the bias voltage is bandgap reference. But bandgap reference can only generate a voltage that is around 1.4V. I need a bias voltage that is higher than 1.4V...What circuit should I use? |
|
|
| Back to top |
|
|
xin
Joined: 02 Nov 2007
Posts: 5
|
| 31 Jan 2008 12:56 Re: Bandgap Reference |
|
|
|
| Normally current mirror is used to bias the opamp. The current in current mirror is often generated from bangbap with a feedback network.
|
|
| Back to top |
|
|
northeast1
Joined: 21 Jun 2007
Posts: 145
Helped: 4
|
| 01 Feb 2008 5:34 Re: Bandgap Reference |
|
|
|
| firsttimedesigning wrote: |
| So I am trying generate the bias voltage of an op-amp. So far the only circuit I know that can be used to generate the bias voltage is bandgap reference. But bandgap reference can only generate a voltage that is around 1.4V. I need a bias voltage that is higher than 1.4V...What circuit should I use? |
You and add a buffer follow the bandgap, and generator what reference voltage you want.
|
|
| Back to top |
|
|
mahgoub
Joined: 26 Oct 2007
Posts: 96
Helped: 2
|
| 06 Feb 2008 10:00 Bandgap Reference |
|
|
|
| how can he use 1.4v for reference to generator higher reference voltage.
|
|
| Back to top |
|
|
remotest
Joined: 12 Feb 2008
Posts: 12
Helped: 2
|
| 18 Feb 2008 6:47 Re: Bandgap Reference |
|
|
|
u can refer the below paper
http://www.edaboard.com/viewtopic.php?p=365207#365207
|
|
| Back to top |
|
|
raghav
Joined: 19 May 2005
Posts: 35
|
| 18 Feb 2008 11:43 Re: Bandgap Reference |
|
|
|
What you could do is to use 1.4 V as a supply to a Nakagome charge-pump, and feed the same 1.4 V as input to the charge-pump. For instance, in the second figure, in the link
http://www.ee.iitm.ac.in/vlsi/courses/ec330_2008/exp2
Vout is twice the supply. What say?
|
|
| Back to top |
|
|
ee07d003
Joined: 18 Feb 2008
Posts: 7
Helped: 1
|
| 18 Feb 2008 16:23 Re: Bandgap Reference |
|
|
|
| Raghav's reply seems helpful. In fact, Nakagome charge pump is used to boost voltages in DRAM cells too. So, it should raise the band-gap voltage to any required value.
|
|
| Back to top |
|
|
jeff_zx
Joined: 08 Dec 2005
Posts: 43
Helped: 2
|
| 25 Feb 2008 15:21 Re: Bandgap Reference |
|
|
|
| qutang wrote: |
| why u are using a bandgap bias the opamp? |
i have the same doubt,especially, voltage bias
|
|
| Back to top |
|
|
kumar123
Joined: 05 Sep 2006
Posts: 61
Helped: 5
|
| 05 Mar 2008 11:44 Re: Bandgap Reference |
|
|
|
| lijianheng wrote: |
| Try this one |
for the figure "bg.jpg" how to choose the characteristics of Opamp used ? or how to test the opamp to be used for this purpose ?
|
|
| Back to top |
|
|
aadis2
Joined: 30 Dec 2007
Posts: 4
|
| 10 Mar 2008 22:48 Re: Bandgap Reference |
|
|
|
hi
i m designing second order curvature corrected band gap reference circuit will anybody help me how to design that
my moses are in cutoff
i m sending one paper on this pz help me
regards
aadi
|
|
| Back to top |
|
|
armixic
Joined: 09 Mar 2006
Posts: 30
Helped: 2
Location: U.S.A
|
| 15 Mar 2008 2:32 Re: Bandgap Reference |
|
|
|
| to bias a opam, a Iref from BG or orther reference is enough. When you need Vref, just dump Iref to a diode-connected MOS.
|
|
| Back to top |
|
|
ashish_chauhan
Joined: 02 Sep 2007
Posts: 181
Helped: 32
|
| 18 Mar 2008 8:21 Bandgap Reference |
|
|
|
Hi
I had designed a bandgap reference... The circuit is doing absolutely fine in simulations... even the post-layouts are also fine. But the silicon shows oscillations at the output and the RMS value is also not 1.2v its way away to 1.9 volts...
any clue to debug.
thanx
|
|
| Back to top |
|
|
qutang
Joined: 25 Oct 2004
Posts: 316
Helped: 5
|
| 19 Mar 2008 7:47 Bandgap Reference |
|
|
|
to ashish_chauhan
maybe you can add a cap. at vdd and output.
|
|
| Back to top |
|
|
asueee0
Joined: 26 Dec 2005
Posts: 136
|
| 27 Mar 2008 2:23 Bandgap Reference |
|
|
|
| 1.4v?
|
|
| Back to top |
|
|
arvkp123
Joined: 30 Aug 2007
Posts: 4
|
| 28 Mar 2008 7:24 Bandgap Reference |
|
|
|
| using a charge pump would be the easiest but you would have to take care of the ripple by using a filter
|
|
| Back to top |
|
|
ashish_chauhan
Joined: 02 Sep 2007
Posts: 181
Helped: 32
|
| 29 Mar 2008 17:34 Re: Bandgap Reference |
|
|
|
| qutang wrote: |
to ashish_chauhan
maybe you can add a cap. at vdd and output. |
I tried that but how much can you cut down through that... the ripples are full fledged oscillations of 1v peak to peak!!!
|
|
| Back to top |
|
|
jecyhale
Joined: 19 Feb 2008
Posts: 371
Helped: 37
Location: China
|
| 01 Apr 2008 7:57 Re: Bandgap Reference |
|
|
|
why not you use the resistor to divide the supply if you don't need a precise voltage.
but if you want to get a precise voltage, you can use a negtive feedback with a opamp.
But usually we don't need a very precise voltage bias. because it is differential pair as the input.
|
|
| Back to top |
|
|
smilelangjun
Joined: 07 Sep 2005
Posts: 37
Helped: 1
|
| 03 Apr 2008 18:21 Bandgap Reference |
|
|
|
| I think the problem is the accuracy of the voltage bias. Do you really need the 0.1% accuracy ? If that ,you can use a kind of bandgap which can generate all values of voltage, in theory, not boter to use LDO,that is pretty a big wast.
|
|
| Back to top |
|
|
heng155
Joined: 19 Nov 2005
Posts: 21
|
| 24 Apr 2008 14:08 Bandgap Reference |
|
|
|
| you can use a opamp as a voltage follower, and a DAC which tuning up the 1.4V and VDD
|
|
| Back to top |
|
|
mady79
Joined: 30 Mar 2004
Posts: 88
Helped: 6
|
| 26 Apr 2008 0:04 Re: Bandgap Reference |
|
|
|
| If u got a supply >2V & a bias current then couple of diode connected mosfet in series is good enough to generate 1.4V .I am assuming bias current is available and not a good idea to build regulator to bias .
|
|
| Back to top |
|
|
yezeg
Joined: 12 Jan 2006
Posts: 15
Helped: 1
|
| 26 Apr 2008 14:21 Bandgap Reference |
|
|
|
could somebody tell me what the beta-multiplier is ?
LDO and charge pump is not a well way
OPA add Resister booster the voltage!
|
|
| Back to top |
|
|
smilelangjun
Joined: 07 Sep 2005
Posts: 37
Helped: 1
|
| 07 May 2008 6:35 Bandgap Reference |
|
|
|
| There are lots of bandap configuration which can generate any voltage value.
|
|
| Back to top |
|
|
bluesea214
Joined: 20 Nov 2007
Posts: 3
|
| 07 May 2008 10:42 Bandgap Reference |
|
|
|
| i f only need a bias voltage ,why ont choose constant gm? u can find in razavi's book.
|
|
| Back to top |
|
|
