[SI-LIST] Re: simulating Mos in series
- From: Parthasarathy Sampath <parthsv@xxxxxxxxx>
- To: super_cop@xxxxxxxxxxxxxx
- Date: Thu, 6 Mar 2003 16:35:35 -0800 (PST)
Hi,
From your netlist, I can understand one thing. You
have given power supply to source of M1, followed by
M2, and M3.
Remember Drain and source in MOS can always be
interchanged and this is one important concept to be
taken into account in Pass transistors.
I belive this is what is happening.
So while you have connected 5v to source to M1, it
acts as drain pushing it into saturation and you see a
vt drop on it. Further down m2 and m3 are in linear
region and nearly 0v across source-drain( viewing from
bottom) and same voltage from x is passed onto pointb.
Hope this clears.
Regards
Partha!
--- super cop <super_cop@xxxxxxxxxxxxxx> wrote:
>
> Hi All,
>
> I am trying to simulate the behaviour of Series
> connection of Mos
> and analyse the max & min voltage the connection can
> pass from i/p
> to o/p.
> although i am able to see the results as in book, i
> ma not able
> to understand the concept or to say i am getting
> confused. let me
> explain.
>
> ***** checking with n-mos connected in series
> m1 x in pointa 0 n l=1u w=5u
> m2 y in x 0 n l=1u w=5u
> m3 pointb in y 0 n l=1u w=5u
> .model n nmos level=1 vto=0.7 kp=110u gamma=0.4
> lambda=0.04
> phi=0.7
> .op
> vin in 0 5
> vdd vdd 0 5
> vpointa pointa 0 dc 5
> .end
>
> If run, this shows voltage at node pointb to be of
> Vdd-thn
> (3.786) i.e max transfered from pointa (5v). below
> is operating
> point information.
> Where i am confused is : when vgs of m1 =0 i.e less
> than vthn,
> won't be m1 in cut-off region since ids =0 when vgs<
> vthn.
> But it shows saturation region.
>
> ***** operating point status is all simulation
> time is
> 0.
> node =voltage node =voltage
> node
> =voltage
>
> +0:in = 5.0000 0:pointa = 5.0000
> 0:pointb =
> 3.7867
> +0:vdd = 5.0000 0:x = 3.7868 0:y
> =
> 3.7868
>
> **** mosfets
>
> subckt
> element 0:m1 0:m2 0:m3
> model 0:n 0:n 0:n
> region Saturati Linear Linear
> id -112.6738p 101.8893f -11.4548p
> ibs -50.0000f -37.8676f -37.8676f
> ibd -37.8676f -37.8676f -37.8673f
> vgs 0. 1.2132 1.2132
> vds -1.2132 296.4245n -32.3396u
> vbs -5.0000 -3.7868 -3.7868
> vth 1.2126 1.2126 1.2126
> vdsat 625.1077u 296.4245n 32.3396u
> beta 576.6913u 550.0000u 550.0007u
> gam eff 400.0000m 400.0000m 400.0000m
> gm 360.4942n 163.0335p 17.7868n
> gds 4.2984p 343.6462n 345.3111n
> gmb 34.0378n 15.3936p 1.6794n
> cdtot 1.1511f 139.9684a 196.3270a
> cgtot 1.2983f 480.4520a 480.7869a
> cstot 2.7930a 196.0400a 140.2611a
> cbtot 144.4435a 144.4435a 144.1988a
> cgs 2.7930a 196.0400a 140.2611a
> cgd 1.1511f 139.9684a 196.3270a
>
>
> How to calculate drain voltage when you know gate
> voltage & source
> voltage forehand. I understand this one's a dump
> one to ask ,
> but i need to . Hope this one's does not intrigate
> any one.
> Thanks in advance for all the help .
>
> Best regards.
>
>
>
>
>
>
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