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sissi
Joined: 25 Feb 2006
Posts: 71
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 06 Apr 2007 8:14 how to understand the slew rate of full differential folded |
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how to understand the slew rate of full differential folded cascode op amp?SR=Iss/CL or SR=ID4/2CL?
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lladnar23
Joined: 20 Mar 2006
Posts: 221
Helped: 32
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06 Apr 2007 16:58 how to understand the slew rate of full differential folded |
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I think it is SR=ID4/CL, assuming CL is connected between Vout- and Vout+.
When the input is railed in one direction, you get the full drain current (ID4) going through either Q5 or Q6. When the input swings to the other rail, the same current switches to the other (Q6 or Q5). So it seems like the current available to charge/discharge CL is simply ID4
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eelinker
Joined: 12 Feb 2006
Posts: 572
Helped: 12
Location: PERSIA
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09 Apr 2007 6:53 Re: how to understand the slew rate of full differential fol |
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| the maximum current which can charge the output cap is simply Id4 when a step is applied at input so S.R>=id4/cl
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sissi
Joined: 25 Feb 2006
Posts: 71
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09 Apr 2007 8:30 how to understand the slew rate of full differential folded |
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hi,
when a step is applied at input ,but a part of ID4 can't change?because Q8 and Q10 operate in saturation.
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pankajdudulwar
Joined: 30 Mar 2006
Posts: 134
Helped: 2
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09 Apr 2007 8:58 how to understand the slew rate of full differential folded |
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| SL= I/CL.where CL is load capacitance. Now using this concept u can analyze the circuit and will get the above equations. In the differential amplifier the current get switch from one branch to the other so consider this also n u will get ur answer
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sissi
Joined: 25 Feb 2006
Posts: 71
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09 Apr 2007 9:36 how to understand the slew rate of full differential folded |
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hi,I see
when ID11>ID4, 5、6 turn off,SR=ID4/CL
when ID11<ID4,SR=Is/CL
so we usually choose ID11<=ID4
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yschuang
Joined: 01 Feb 2004
Posts: 189
Helped: 15
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09 Apr 2007 10:25 Re: how to understand the slew rate of full differential fol |
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So, for example.
when ID11>ID4, 5、6 turn off,SR=ID4/CL
Given Id4=0.9Iss ,Id11=Iss ,
therefore SR=0.9Iss/CL
when ID11<ID4,SR=Is/CL
Given Id4=1.2Iss ,Id11=Iss ,
therefore SR=Iss/CL
However, I do not think so.
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sissi
Joined: 25 Feb 2006
Posts: 71
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09 Apr 2007 11:06 how to understand the slew rate of full differential folded |
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| What do you think?
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hr_rezaee
Joined: 06 Oct 2004
Posts: 892
Helped: 88
Location: Iran-Mashhad
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09 Apr 2007 18:39 how to understand the slew rate of full differential folded |
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Hi
normal state:
I4=I2+I8 (1)
large and fast input:
Q2 is turn off.
then
Iout-=I4-I8
from (1) =>
Iout=I2=0.5*I11
sr-=0.5*I11/Cl
simar above
sr+=-0.5*I11/Cl
=> SR=I11/Cl
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yschuang
Joined: 01 Feb 2004
Posts: 189
Helped: 15
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10 Apr 2007 2:51 Re: how to understand the slew rate of full differential fol |
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| I agree with hr_rezaee.
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sissi
Joined: 25 Feb 2006
Posts: 71
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10 Apr 2007 3:01 how to understand the slew rate of full differential folded |
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hi,
if ID11>ID4, how is it going on?
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hr_rezaee
Joined: 06 Oct 2004
Posts: 892
Helped: 88
Location: Iran-Mashhad
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10 Apr 2007 6:44 Re: how to understand the slew rate of full differential fol |
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| sissi wrote: |
hi,
if ID11>ID4, how is it going on? |
Hi
in my equations for any state that I4=I2+I8
answer is I11/Cl
so for I11>I4, it will be I11/Cl.
regards
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sissi
Joined: 25 Feb 2006
Posts: 71
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10 Apr 2007 9:20 how to understand the slew rate of full differential folded |
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hi, hr_rezaee
i have gotten the answer.I11>I4 should be avoided when we desing.
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