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202 Threads found on Vth Vgs
why low vth device has higher noise than high vth device? Thanks.
Hi everyone, I have 32nm level 54 Nmos model. I want to simulate the change of threshold voltage accroding to channel length in LTspice but I do not know how. When I make dc op, it does not show vth directly. with linear extrapolation technique, vth can be found but it does not still show vth directly so how can I simulate (...)
If you review an analog IC design textbook (e.g. Razavi) you'll find criteria to determine the region when knowing Vds, vgs and vth. Usual SPICE simulators don't display the region (Some Cadence tools do, I believe), but could write measurement expressions that show it.
Hi guys, Allow me to ask you a question, since you are talking about Vdssat. In cadence, when you do annotate you get some of the mosfets parameters like vdsat, vds, vgs, vth, vbs, etc. Now, when you are designing a circuit we know that, depending if you are designing for strong inversion, moderate inversion or weak inversion, how do you guys int
IRF630 has vth of 2 to 4V and specified Rdson for 10V vgs. It can't be successfully operated with 5V or even 3.3V driver supply. Either choose a "logic-level" MOSFET or use high driver supply. IRF630 has 9.3A continuous Id rating, it can't work at 9A without a large heat sink. It's also 200V class, not suggested for a low voltage application. Yo
in a paper what is meant by sub-Vt saturation region ? i know it isn't the normal saturation region where VDS>vgs-vth. does the above expression mean its the maximum current that can be drawn in the sub-Vt domain ?
RdsOn applies when vgs >> vth Rout applies when vgs ~ vth and used for gain control or linear operation
Yes, vgs can be less than vth. Making them in the sub-threshold region has higher gm/id, more power efficiency and higher gm, which is good for noise minimizing and matching. If you want very high bandwidth, you need to make it in the saturation region, making vgs > vth.
High vth in power FETs means a high gate voltage swing means high switching losses. In IC technology, you have to position VT to best deal with the leakage power vs drive strength / speed "box". Here you often see multiple VTs in the same flow so that you can optimize near-static logic, and high speed clocked circuitry separately. An "easily in
Hello! Excuse my ignorance but I was reading about Photovoltaic Generators used as FET drivers, and the implication appears to be that operation only requires an initial pulse signal to drive a FET vth on, with the PVI driver having it's own floating voltage source to manage the FET vgs threshold. Is this correct? It's hard for me to wrap
Hi, with ADE, you can use the calculator (tools->calculator) and add vgs-vth as value to save. Then add gm = ids/vds, also with calculator. After somulation, in plot window, choose Y vs Y, that's it. No idea in command line, but feasible, because spice can do it. Regards
When vgs is > vth it means above the threshold of saturation and must have a supply of current available between Vds so thus Vds is not zero and the voltage drop is the standard spec characteristic of RdsOn. When vgs = max i.e. >> vth then it is fully saturated and reached the maximum conductance or best case low RdsOn. (...)
The shown equation is just a rather crude approximation. See here the context of Veff = vgs - vth and Vdsat vs. Inversion coefficient: 123383 ... derived from data from the book mentioned in the following diagram, which shows the relationship between Vdsat and drain current of a certain nMOS in all regions of its inver
1. I think you mix up the overdrive voltage Vod with the drain-source voltage Vds. The usual definition of Vod is vgs = vth + Vod (... where Vod would be negative for subthreshold operation), whereas in your definition the overdrive voltage of th
Drain-bulk current should be sufficient to explain off-state current flow. Not off-state, saturation mode is meant: vgs > vth , and Vds > vgs - vth (pinch-off).
Hi all i am working on subthrshold region using pfet. I have done this before using nfet and using voltage source. I have good idea abt nfet where vgs < vth and VDS can be neglected no matter wat the value is if its above vth. But could anyone pls tell me how is it for pfet transistor. In nfet i used two voltage sources vgs (...)
In the linear region a rds can be descript by rds = 1/(mu Cox W/L (vgs-vth)). In a mos-cap VDS is equal to zero but what's the value for rds when vgs<vth oder vgs<0? In such cases you obviously can't use this equation. Instead use rds = VDS/(mu Cox W/L) = VDS/Id For VDS -> 0 --> rds -> ∞
I am not sure if I understand the question, but as I see it the transitor will be in linear/triode mode until vgs>vth and Vds<(vgs-vth). If this is true node B will more or less folow node A. BR Jerry
Actually, first one is a MOS transistor transconductance formula. And I think it is incorrect. it should be 2*Id/(vgs-vth) or sqrt (2*Un*Cox*Id). Second one is not gm of single transistor. This is probably effective gm of an amplifier and if Cc is compansation capacitor, it is probably a two stage miller opamp. In every situation, gm of a mos trans
You are generally limited by the gate-source threshold voltage (vgs(th)) so you want transistors that have a low threshold. I don't completely object to this but I don't completely agree either. Yes vth is important but in ideal case you'd be able to go beyond gate voltage by vth (assuming you don't care about accu
Hi guys, I have got a very simple netlist that I trying to simulate in Hspice: MN1 VCC Gat 0 0 CMOSN L=360n W=360n VDD VCC 0 DC 1.8 vgs Gat 0 DC 1.43 .OP 1us .END The model used is 0.18micron TSMC. In the model K' is defined as (?Cox/2) = 177.2uA/v? and vth =0.43v. Base on
Make sure that the current mirrors have adequate vgs-vth and Vds-Vdsat margins. Say about 100mV or so. That will help a lot with mismatch. Chopping can help you get rid of the Op-Amp offset.
Hi, This feature exists in Cadence Spectre, but, at the moment, it seems that spice is lacking this feature. At least, you can print vgs, vth and vds, but you have to determine operating point by yourself. If I am wrong, I am also very interested in a way to do that (especially with ngspice).
Hi guys, In CMOS Circuit Design, Layout and Simulation by R.Jacob Baker page 300, Table 9.2 shows the parameters for short channel MOSFET. These are the parameters given: Id = 10uA vgs = 0.350V vth = 0.280V Cox = 25f F/um^2 W = 2.5um L = 100nm I'm trying to calculate back using Id equation and the parameters given to get the value W/L
Hello, Here is the weak inversion equation that I know: Ids=2*n*u*Cox*vthermal?*exp((vgs-vth)/(vthermal*n)) Now, I've got a few questions about this: 1) How does the Vds dependency of Ids play in? On MIT open course, I've found the add-on (1-exp(-Vds/vthermal)) to be multiplied with the above (...)
Hello, Classically a MOSFET is saturated when Vds > vgs - vth ... (vgs - vth = vov). However Ive recently started working on a more modern process where Vds_sat is used to indicate the onset of saturation and not Vov. However Vov and Vds_sat are not the same. Physically I understand that when Vds > Vov the (...)
... I want to get information about operating conditions of each transistor(like gm,vgs,vth,id etc) . How can I get these parameters and which type of analysis on symbol will yield these parameters? The same as for an analysis on schematic: DC . In the simulation stop list, "schematic" must be prio
A MOSCAP requires a minimum voltage across it to give the maximum capacitance. It gives the maximum capacitance when it is in strong Inversion i.e. the vgs > vth when the channel is full formed. Check Razavi's "Design of Analog CMOS Integrated Circuits" page 39. Btw, MIMCAPs ca be placed over active devices and therefore might not be as much
In old CMOS processes, where the square law was a good approximation, vdsat should indeed be equal to vgs-vth when the transistor is in strong inversion and channel modulation can be ignored (long L). In your case the transistor is in moderate inversion as vgs is almost equal to vth. Try to make vgs a little (...)
... whether it is in SATURATION or SUBTHRESHOLD region. SUBTHRESHOLD is not a region, but an operation mode. A MOSFET can be operated in SUBTHRESHOLD mode (vgs < vth) and simultaneously in SATURATION region (Vds > Vds,sat).
Hi, I read in Behzad Razavi CMOS book that overdrive voltage of MOS is dependent of W/L ratio. I am confused about this because Isn't overdrive voltage vgs-vth volts?. Can't i control overdrive voltage by changing vgs voltage by myself. For example, if vth= 0.5V and i put vgs =0.7 then overdrive (...)
Ok, but from your dc point result i don't see a triode region, this is cutoff, vgs < vth. Why do you connect bulk of T6 to it source? Do you want make overdrive voltage smaller with it? And such kits usually has a special lvt models for transistor.
Hi all: I am designing a OPA and I set the input gm = 10uA/v = upCox*W/L*(vgs-vth)=(2*upCox*W/L*Id)^(1/2), but I found the upCox doesn't a constant value, it changes with W/L or vgs or vds. How to know the upCox value? Thanks for your reply. mpig
Hi all, I upload a file. In this word there are figure related to my questions. If I have a common source amplifier (figure 1), If I want to amplify a signal vgs, this signal should be greater than vth for the conduction of the MOSFET, for that reason I use a constant value vgs for the polarization of the mosfet. But for example if (...)
Hi all: I simulate the Temp vs vth and Temp vs id of relationship of NMOS. 1. Temp = 27C, vth = 0.73V, id = 30uA when vgs = 1.6V, vds = 5V @TT 2. Based on item#1, I sweep temp to know Temp vs vth and id @ TT a. when temp is increased, the id is decreased b. when temp is increased, the vth (...)
Hello, I was doing some circuit in cadence and i suddenly noticed that the NMOS is in saturation but the condition of saturation Vds>= vgs-vth is not met.. Instead Vds is less than vgs-vth and still it is in saturation. My Vds = 0.4617 V vgs = 1.16 L = 180nm W = 240nm Please some one help me in (...)
For a PMOS just consider all the things as negative. in your case you mention Vds as 0.6V. This would mean that Drain is 0.6V higher than Source. This would be incorrect for a PMOS. What you mean to say is Vsd = 0.6V => Vds = -0.6V vth = -0.2V Therefore, Vds + vth < vgs < vth i.e. -0.8V < vgs < -0.2V (...)
Hi I am confused about how to control overdrive voltage of MOS. I read that overdrive voltage can be made smaller by increasing W/L ratio of MOS. Why is like that? I think that as overdrive voltage definition is vgs-vth, therefore, overdrive voltage should only be controlled by increasing or decreasing vgs. Moreover, sometimes i have seen in (...)
hi all , i saw this curve in many books ,I knew in mosfet id=gm(vgs-vth),but when vds is falling , IL=(VIN-VDS)*t/L,IL=ID which should be rising ! so id should be constant or rising? the picture shows me it is constant ,why?:?: 96672
Thank you erikl. When vgs is slightly lower than vth, body is depleted in the surface under gate oxide. So here is a depletion region between drain and source. Drain/body and source/body junctions are reversed biased, so they have their own depletion regions. In this condition, drain's depletion region, source's depletion region, and depletion r
hello from the definition, the threshold is the gate-source voltage at which the transistor start to conduct the current on it its drain. this is about 0.5V in your graph. any way the exact value of the threshold voltage still not fully defined as the transistor even start to conduct before this voltage in what we called sub threshold voltage. bu
Overdrive voltage VOD = vgs-vth . Normally you get the vth from the device model specs. Normally for hand calculation you can assume 200mV of VOD. The purpose of VOD is to calculate the conditions of a circuit that needs to be sufficiently 'ON' rather than being close to subthreshold region. If you have simulation tools you could simulate it (...)
Hi, i think that there we may have 2 ways: 1. Ideal current source in drain. There are transistor in saturation until vgs > vth, because any changes in vgs > vth doesn't change drain current (ideal source). If vgs goes below vth we have open circuit and therefore no current. 2. (...)
1. Do a dc operating point simulation of a NMOS and PMOS with vgs = 1V and Vds = 1.8V. (Or any other values of your choice.) 2. Find out Id and vth of both transistors from the operating point 3. Use the equation Id = 0.5?nCox(W/L)(vgs - vth)2 and calculate ?nCox 4. Try this out for different values of W/L, (...)
The problem is with the NMOS transistor. For a NMOS transistor with gate at Vdd and Drain at Vdd, the source can be at most Vdd-vth, any higher than this voltage, and the NMOS would be in subthreshold, i.e. OFF. This is why you see a voltage drop of 1.2V which is the vth of the transistor. You need to use a PMOS switch to pass Vdd or both NMOS
I encountered this equation in CMOS conventional 2-stage opamp theory. Slew rate = (vgs-vth)*WT vgs-vth is bias condition on input transistors. And WT is Gain-bandwidth product. I'd like to know how to get the equation and understand the reasoning on it. Any paper or article about it would be really appreciated. (...)
I think you're considering vgs = vin. As I understood from what you wrote vgs = V1, so now its not important what vin is , the transistor considers vgs and therefore produces a drain source current of ids=gm*vgs. Therefore the vth will be vin (the main input ) and the rth will be 1/gm. I think you have (...)
If you put out the factor (1/2)*Vds from the expression in the square bracket in equ. (2.8), you stay with Id = u*Cox*(W/L)*(1/2)*Vds*. If you now want to disappear the summand Vds in the square brackets by claiming Vds << 2(vgs - vth) , you arrive seamlessly at Razavi's equ. (2.10). So mathematically it's quite ok, I think.
You can just use the equation Id = 0.5 Kn (W/L) (vgs - vth)2 (1 + λ Vds) Do the simulation for Different Id, vgs, Vds, You have two unknowns Kn and λ which you can then calculate. These values will change with the operating conditions. λ will vary with Vds and Id and a lot of other parameters. You might have to do a bunch of (...)
Regarding (4). I think that you need to have a sufficient margin from vgs to vth (my guess is 100m-150mV) otherwise they are going to move from weak inversion. If you use spectre you can see the region of operation. Check that the region=3 for weak inversion. Also the mos (not the one above the resistor) usually has higher vgs than the other (...)