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| Who can help me to analysis this AMP? | ||
| Author ken7976 Views 3 Posted at 2008/8/27 15:24 [View In Forum] | ||
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The architecture of amplifier is fromjzwligtt jzwligtt Op-amps and startup circuits for CMOS bandgap references with near 1-V supplyjzwligtt jzwligtt Boni, A.;jzwligtt jzwligtt Solid-State Circuits, IEEE Journal ofjzwligtt jzwligtt Volume 37, Issue 10, Oct. 2002 Page(s):1339 - 1343 jzwligtt jzwligtt Digital Object Identifier 10.1109/JSSC.2002.803055 jzwligtt jzwligtt jzwligtt jzwligtt Summary: The design of bandgap-based voltage references in digital CMOS raises several design difficulties, as the supply voltage is lower than the silicon bandgap in electron volts, i.e., 1.2 V. A current-mode architecture is used in order to address the mai.....jzwligtt jzwligtt jzwligtt jzwligtt The questions are:jzwligtt jzwligtt 1. How to realize the common mode feedback by using m1, m2, m0a and m0b in the input stage.jzwligtt jzwligtt 2. The m1, m2 m0a and m0b operate in weak inversion. How to achieve 60 dB DC gain of such amplifier?jzwligtt jzwligtt 3. Does m5 and m6 operate in weak inversion too, or in saturation region?jzwligtt jzwligtt Thank you!! |
| Reply No. | Replier | Total Replies 13 [View All Replies] [New Reply] | Replied at |
| 1 | bubulu | 1. This is typical CMFB circuit. When Vin-com increases, Vgs(m0a) and Vgs(m0b) decrease, let the Vgs(m1) and Vgs(m2) stable. 2 & 3. M1, M2, M3, M4, M5, M6 are in saturation, they determine Gain. By the way, Do you want to use this circuit? |
2008/8/27 15:24 |
| 2 | gao51755775 | 2008/8/27 15:24 | |
| 3 | chdd | Hi For M5 I'm sure that it's not in inversion, but in saturation mode. Because it' connected like a diode. For MOA and MOB i'm also sure that schould be in deep inversion mode. But for input differential transistors i quite strange to stay in inverse mode. Try to "play" with dimension of transistors to achieve saturation mode. Do the same for output stage. I think that also M6 schould be in saturation. Regards |
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| 4 | zunwang | What are the merits of common mode feedback? why the common mode feedback is used? |
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| 5 | knoxville | Hi I think that both transistors M0A and M0B are in fact resistors which are used for differential stage polarisation. So if would you use only one than voltage changes on drain of differential transistors would infect seriously your DC point. This way it is balanced. My question is how good this resistor in your compensation path is? I mean tolerance, temperature dependencies, linearity etc. Regards |
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| 6 | ct731 | 2008/8/27 15:24 | |
| 7 | edu | Yes I'm quite sure. The question is why not normal resistor. That's why I asked for resistor parameters. Regards |
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| 8 | gao51755775 | 2008/8/27 15:24 | |
| 9 | wyslnhhh56 | Hi Sorry I just cannot read this e-mail now. If it's not late I can replay toomorow. Well concerning this amplifier, I simply don't think that you need common mode feedback here. This is single ended amplifier. They just used this mosfets like a resistor, because of small suply voltage they cannot use normal current source. My question was why not normal resistor, because you can achieve better stability if the resistor is with enough googd characteristics (temperature, parasitics and so on). The possible answer is that for this technology there is no qualty resistor. But then I saw it in compensation path. Because with normal resisto you are going to have polarisation current enough stabile concerning voltage of input transistors (of course if they are in saturation) Concerning CMFB. One characteristic is preservation of stabile output signal when is no diferential exitation (this one you don`t need because you use single-ended output).The other one is more side effect it schould be made so that doesn' t afect polarisation of amplifier. I think that designer is using here this second one. Because if gate of M0A goes high because of aplied diferential voltage than other scould go down for the same amount of voltage. That means that first transistor's resistivity is smaler and second one is biger for some amount (which schouldn't be big concerning linearity) I hope that this is frome some help Regards |
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| 10 | bubulu | Thank you zajbanlik. I already read the Allen's book: CMOS analog circuit design. In the chapter 7.3 Differential-output op amps, the CMFB is used for differential in differential out opamp topologies to keep the output common-mode voltage midway. From the attached paper, I think that the main merit of such CMFB in input differential pair stage is low-voltage application. Second is to stablize the DC operationg point. And I already understood the principle of CMFB loop. Thanks again! |
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