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# Long Channel Device

18 Threads found on edaboard.com: Long Channel Device

## How to get un*cox from a given technology through simulation

long channel device (like 10x10), pull an ID-VG curve, extract VT0 in the usual way, and back u0*Cox out of the equation you'd be looking to use it in (ID=w/l*u0*Cox*(V-VT)^2 or whatever).

## Layout of PMOS source and Cascode

Ask yourself what upside there is, in a long channel cascode device? The axiom is, if it doesn't buy you something, then stick with the minimum cost (area). You would generally prefer that the source of the cascode guard device move as little as possible, acting as a stiff source follower. That argues for minimum L, (...)

## MOS substhreshold operation

In BSIM3 and BSIM4 models the only discontinuity exists between inversion regions so if OP of your transistor is quite deep in weak inversion You shouldn't see nothing "numerical". Remember that any drain current equations showed in books are only the first approximations based on number of assumptions/simplifications. And if You checked Gray's b

## MOSFET threshold voltage (vth) dependance on channel length

Let's start from "old" technologies (technology node ~0.25 um or older). According to a classical MOSFET theory, Vt of a long-channel device is independent of the channel/gate length. If channel length is decreased, depletion regions around source/body and drain/body p-n junctions start to overlap, and the (...)

## threshold voltage will it vary with shorter technology as compare to bigger technolog

Yes it will. Data from Baker Book. Threshold voltage long-channel device NMOS 800mV PMOS 900mV Short-channel device NMOS 350mV PMOS 350mV

## layout long l devices

hey all, i have a current mirror where the currentmirror is a long l device. can i spilt this device into several devices with the same width and a shorter l? what about the current matching when doing it this way? regards zitty

## Must i use a long channel device for "soft vcc"

Hi, Is there a big impact if i replace the long channel device with short channel device for softvcc purpose?

## Leakage for very long channel devices

Do you know leakage problematics for very long channel devices (i.e. > 100 um, up to 500um or 1 mm ) ? I'm well aware of S-sub and D-sub inverse saturation current, but that's not my doubt. I'd like to know from you if phenomena like "channel-to-substrate" leakage occur, and eventually how to model them.

## Transistor Channel characterization

Any transistor where the older "LEVEL=" MOS model does a good job, or the measured data looks like the curves you see in basic textbooks, is "long". Any transistor that looks like somebody sat on it, is "short". If the foundry calls it a digital device, it's "short". Guaranteed. :) Back in the day, 1um was short.

## Layout: Any risk put two w<<L transistor close?

As posted before there is a field implant in between. If there is a poly wire above field oxide but between the two long (L>>W) MOS it could create a channel. The device is the parasitic field oxide MOS which has a threshold voltage typical higher than the maximum supply voltage. But below the threshold voltage the subthreshold current could (...)

## is there any velocity saturatin in long channel MOSFETs?

there any velocity saturatin effect in long channel MOSFETs? 2.does velocity saturation lead to an equidistance current increase as incease the gate voltage with same range? i've checked for the plot for long channel device and found that the current increase respecting to gate voltage increase is not (...)

## Channel Length for Analog Design

If you want to use a mosfet as a current mirror then long channel will be better than a short channel device due to channel length modulation effect. also using cascode current mirror is an option to increase output resistance. But you cut from the headroom by using cascodes. As sridhar540 mentioned (...)

## Current source transistor size for DAC

Hi, I calculated the size of the current source for the DAC, but the size came out to long channel and narrow wide, about 3/20 I think the transistor could be operated in the weak inversion region with that size. Is there any problem on that? Thanks,

## long channel and short channel

Inside Simon Sze's Semiconductor device Physics. There is a defination when will be short and when will be long. The effective channel length and electrical field are teh domain one. If from tehcnology bench mark, beow 0.25um it will be easy to get into short channel effect.

## Very strange problems about bandgap

to sum up . bandgap use parastic Pnp device and consider Resistor variation , no trim bandgap will drfit some voltage .. another problem is "density or concentration" I ever met , from WAT restsor data is Ok , but really bandgap design use 2 long channel resistor . and cause resistor value mismatch . WAT only measure little square (...)

## how to obtain very large resistors

1. use Hi-Res resistor .. some process have un-dope poly close 1~3K/square , SRAM Hi-res have 1G~2G/squre and use long snake shape 2. use mos switch , but long channel > 20um you should know , spice model maybe have error in gerneal , spice model is fitting for short channel device 3. use (...)

## What is the difference b/w VOD and VDSAT?

For long channel device Vod equal to Vdsat For short channel device There existed a lot of second order effects So Vdsat is not simply equal to Vod If you want to find out how the hspcie get the vdsat you can refer to the hspice manual, model level. While in hand calculte we use vod(vgs - (...)

## How to implement long channel device (layout and schematic)?

this long channel devive maybe is used as current source for current-steering DAC with very large output impedence.