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icekalt Community Member Offline Posts: 36 Aalen, Germany	How to calculate bias current Jun 15^th, 2009, 5:45am Can someone explain@help to determine the value of Ibias? You can find the circuit in the attachment. VDD is 3.3V and the MOS technology used is 0.35�m. thx in advanced
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raja.cedt

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Re: How to calculate bias current
Reply #1 - Jun 15^th, 2009, 6:03am

hi,
thats mainly in your hand only, i guess this is a first stage of an comparator, so based on the input resolution you might have some gain and you know how much time in your hand for first stage so based on that how much gm you need and for that gm you can find how much current in the input differential pair and double of that current is what you want.Listen this is the not only the way...
Thanks,
rajasekhar.

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pancho_hideboo Senior Fellow Offline Posts: 1424 Real Homeless	Re: How to calculate bias current Reply #2 - Jun 15^th, 2009, 6:12am icekalt wrote on Jun 15^th, 2009, 5:45am: Can someone explain@help to determine the value of Ibias? As draft design, you can determine Ibias if you determine required intrinsic gain and required slew rate and load capacitance.
Back to top	Kita━━━━━━(ﾟ∀ﾟ)━━━━━━ !!!!! http://www7.plala.or.jp/ungeromeppa/flash/kita.html http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related IP Logged

raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: How to calculate bias current Reply #3 - Jun 15^th, 2009, 6:31am hi, i forgot to ask ,how did you come up with diff amp w/l ratio,don't you consider current in that case? Thanks, Rajasekhar.
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icekalt Community Member Offline Posts: 36 Aalen, Germany	Re: How to calculate bias current Reply #4 - Jun 15^th, 2009, 6:49am raja.cedt wrote on Jun 15^th, 2009, 6:31am: hi, � i forgot to ask ,how did you come up with diff amp w/l ratio,don't you consider current in that case? Thanks, Rajasekhar. i just randomly selected it..:)
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icekalt

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Aalen, Germany

Re: How to calculate bias current
Reply #5 - Jun 15^th, 2009, 6:56am

pancho_hideboo wrote on Jun 15^th, 2009, 6:12am:

icekalt wrote on Jun 15^th, 2009, 5:45am:

Can someone explain@help to determine the value of Ibias?

As draft design, you can determine Ibias if you determine required intrinsic gain and required slew rate and load capacitance.

hello pancho_hideboo,

are you referring the load capacitance to the diode connected loads(two PMOS)?

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pancho_hideboo

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Re: How to calculate bias current
Reply #6 - Jun 15^th, 2009, 7:09am

icekalt wrote on Jun 15^th, 2009, 6:56am:

are you referring the load capacitance to the diode connected loads(two PMOS)?

Right although they are not diode connected loads.

http://www.zen118213.zen.co.uk/RFIC_Circuits_Files/MOS_OP-Amplifier_Intro.pdf
http://www.zen118213.zen.co.uk/RFIC_Circuits_Files/MOS_OP-Amplifier_Example.pdf

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Kita━━━━━━(ﾟ∀ﾟ)━━━━━━ !!!!!
http://www7.plala.or.jp/ungeromeppa/flash/kita.html
http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related

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uu@uk Junior Member Offline Posts: 17	Re: How to calculate bias current Reply #7 - Jun 15^th, 2009, 8:30am Hi, What is the amplifier for? If it is driving capacitors and you need high swing at the output. The slew rate may also give you some idea about the bias current. Thanks uu@uk
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HdrChopper Community Fellow Offline Posts: 493	Re: How to calculate bias current Reply #8 - Jun 15^th, 2009, 1:20pm Hi, On top of what was already suggested, also input noise and offset levels might be controlled by means of Ibias. Regards Tosei
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icekalt

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Re: How to calculate bias current
Reply #9 - Jun 16^th, 2009, 5:34am

uu@uk wrote on Jun 15^th, 2009, 8:30am:

Hi,

What is the amplifier for? If it is driving capacitors and you need high swing at the output. The slew rate may also give you some idea about the bias current.

Thanks

uu@uk

thx uu@uuk. The amplifier is for the comparator. It has to amplify the difference of two signals.

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icekalt Community Member Offline Posts: 36 Aalen, Germany	Re: How to calculate bias current Reply #10 - Jun 16^th, 2009, 5:37am What is the best analysis to simulate that circuit? transient or ac or dc sweep??
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icekalt

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Aalen, Germany

Re: How to calculate bias current
Reply #11 - Jun 16^th, 2009, 5:44am

pancho_hideboo wrote on Jun 15^th, 2009, 7:09am:

icekalt wrote on Jun 15^th, 2009, 6:56am:

are you referring the load capacitance to the diode connected loads(two PMOS)?

Right although they are not diode connected loads.

http://www.zen118213.zen.co.uk/RFIC_Circuits_Files/MOS_OP-Amplifier_Intro.pdf
http://www.zen118213.zen.co.uk/RFIC_Circuits_Files/MOS_OP-Amplifier_Example.pdf

halo pancho_hideboo,

I just have read through the documents. Do you have example for differential amplifier used in comparator? the one that you give me is used in op-amp..thx

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uu@uk

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Re: How to calculate bias current
Reply #12 - Jun 16^th, 2009, 10:14am

icekalt wrote on Jun 16^th, 2009, 5:37am:

What is the best analysis to simulate that circuit? transient or ac or dc sweep??

If your amplifier is for a comparator, I think you need both transient and DC analysis. transient could tell you the rise/fall edge rate. DC analysis can check the FETS are all working in the right region. good luck.

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icekalt

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Aalen, Germany

Re: How to calculate bias current
Reply #13 - Jun 17^th, 2009, 7:15am

uu@uk wrote on Jun 16^th, 2009, 10:14am:

icekalt wrote on Jun 16^th, 2009, 5:37am:

What is the best analysis to simulate that circuit? transient or ac or dc sweep??

If your amplifier is for a comparator, I think you need both transient and DC analysis. transient could tell you the rise/fall edge rate. DC analysis can check the FETS are all working in the right region. good luck.

Thx uu@uk. Can you explain me more about rise/fall edge? How to know if our MOS transistors working in the right region based on simulation? thx

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