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henrytqy Junior Member Offline Posts: 28	change the position of Rc&Cc for the miller effect Nov 09^th, 2011, 5:31pm [img][/img] If I change the position of the Rc & Cc, how can we explain the miller effect. Does it have other effect on the whole circuit? Thanks~
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rajkumar palwai Community Member Offline Posts: 46 Sunnyvale, California	Re: change the position of Rc&Cc for the miller effect Reply #1 - Nov 9^th, 2011, 8:58pm Henry, Miller effect doesn't change if u interchange the Rc & Cc positions. The circuit functionality remains same.
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henrytqy

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Re: change the position of Rc&Cc for the miller effect
Reply #2 - Nov 9^th, 2011, 11:08pm

rajkumar palwai wrote on Nov 9^th, 2011, 8:58pm:

Henry,
Miller effect doesn't change if u interchange the Rc & Cc positions. The circuit functionality remains same.

Yes, I think so.
In integrated amplifiers if Rc is implemented with a mos transistor,in most cases it is usually place first to better control the resistance of the transistor. Do you know that why "better control"?

Thanks~

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rajkumar palwai

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Re: change the position of Rc&Cc for the miller effect
Reply #3 - Nov 10^th, 2011, 1:19am

In the amplifer, we keep the Rc to cancel the zero caused by the gm2&Cc. So ideally Rc should track gm2 across process corners.

Now gm2 =K(Vgs2-Vth2). And we implement the Rc with a PMOS in linear region whose gds=k(Vgs-vth2). So if u connect the Rc and Cc in the order as shown in the figure, then the same node goes to the gate of M2 and source of Rc and hence u can control the Rc bias accurately.

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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: change the position of Rc&Cc for the miller effect Reply #4 - Nov 10^th, 2011, 1:22am hello, There is no much diference... may be first stage has lesser swing becaz of gm2, so if you use an mos as resister then Vgs may not change. and moreover control for the resister will come from replica bias, so to track better not to have any swing. Thanks, raj.
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RobG

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Re: change the position of Rc&Cc for the miller effect
Reply #5 - Nov 10^th, 2011, 8:15am

henrytqy wrote on Nov 9^th, 2011, 11:08pm:

Yes, I think so.
In integrated amplifiers if Rc is implemented with a mos transistor,in most cases it is usually place first to better control the resistance of the transistor. Do you know that why "better control"?

Thanks~

Yes, you think correct for a mos resistor. In that case, you want the mos resistor on the left. The resistance is controlled better there because the voltage at the "-" node of the gm2 stage varies only a small amount, thus the gate-source voltage of the mos resistor is relatively independent of the output voltage. On the other hand, the output of gm2 can swing rail-to-rail. �If you want the mos resistor on the right side of the cap you need to make it a tgate. For example, if you just use an NMOS it will turn off when the output is low leaving you with no compensation.

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weber8722 Community Member Offline Posts: 95	Re: change the position of Rc&Cc for the miller effect Reply #6 - Nov 17^th, 2011, 7:59am I would leave the positions as drawn . If Cmiller is big, than also maybe its bottom-plate cap, so have this at the driven side - i.e. at the op-amp output!
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RobG Community Fellow Offline Posts: 570 Bozeman, MT	Re: change the position of Rc&Cc for the miller effect Reply #7 - Nov 17^th, 2011, 11:15am weber8722 wrote on Nov 17^th, 2011, 7:59am: I would leave the positions as drawn . If Cmiller is big, than also maybe its bottom-plate cap, so have this at the driven side - i.e. at the op-amp output! Good point about the bottom-plate parasitic
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