Affirma Spectre DC Device Matching Analysis Tutorial - Cadence ...

Affirma Spectre DC Device Matching Analysis Tutorial
∂
The term Vout in (2) is the sensitivity of the output to the drain to source current
∂ΔIdsi
and can be efficiently obtained in a standard way as outlined in part b.
a- Mismatch models
The term σ is the variance of the mismatch current in Mosfet transistors. The
mismatch in the current is assumed to be due to a mismatch in the threshold voltage
( ) and the mismatch in the width to length ratio ( ). It is approximated as:
2( ΔIdsi) Vth β
where
gm o
= ∂Ids
----------- ,
∂Vth
Idso
2
gmo σ2( ΔIds)
( Ids0) 2
----------------------
( Ids0) 2
-----------------σ 2 σ
( ΔVth)
2( Δβ)
=
+ -----------------
2
βo and currently, as implemented in Spectre:
σ2( ΔVth)
σ2( Δβ)
( β0)
2
----------------- =
=
mvtwl 2
-----------------
WL
mvtwl22
WL2 -------------------- mvt0 2
+ +
mbewl 2
------------------ mbe0
WL
2
+
, (EQ 3)
Note, that gmo is computed at the DC bias solution from the device model equations,
the values a, b, c, d and e are the mismatch parameters while W and L
are device
parameters.
Another way of representing the mismatch current is using the gate voltage variation
defined as:
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