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

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Affirma Spectre DC Device Matching Analysis Tutorial Mismatch modeling 1. Use Model After identifying the output, the user needs to specify the parameters for each device contributing to the mismatch. Currently, The mismatch model implemented in Spectre for Mosfet transistors introduces five additional model parameters, one for bjts and nine for resistors. To start the dc-mismatch analysis, the user types the analysis statement with the output voltage on which the dc-mismatch analysis is to be performed. The results are: 1) The 3-sigma random output variation 2) The dc operating point information 3) For each Mosfet: • 3-sigma output variation, • 3-sigma Beta variation, • 3-sigma Threshold voltage variation, 3σ(ΔVth) • 3-sigma gate voltage variation, 3σ(ΔVg) • 3-sigma current mismatch to nominal current ratio, 4) For each BJT • 3-sigma output variation, ∂ 3σ( ΔIds) Vout ∂ΔIds 3σ( Δβ) -----------------β0 ∂ 3σ( ΔIc) Vout ∂ΔIc • 3-sigma Vbe Variation, 3σ(ΔVbe) 3σ( ΔIds) ----------------------- Ids0 Release Date Back Page 14 Close 14
5) For each Resistor Affirma Spectre DC Device Matching Analysis Tutorial • 3-sigma output variation, • 3-sigma Resistor current mismatch to nominal resistance current ratio, • 3-sigma VR variation, 3σ(ΔVr) = 3σ(ΔIr).R • 3-sigma IR variation, 3σ(ΔIr) • 3-sigma Resistor variation, We define a threshold mth, below which the contributions will not be shown, currently, in spectre mth = 0.1%. Mth is an analysis parameter. 2. Summary of Theory. Statistical variation of drain current in a MOSFET is modeled by: where: Ids Ids o ΔIds ∂ 3σ( ΔIr) Vout ∂ΔIr 3 σΔIr ( ) ----------------R Ir0 ds = Idso+ ΔIds -- is the total drain to source current. -- is the nominal current. 3σ( ΔIr) -------------------- Ir0 , (EQ 1) -- is the variation in drain to source current due to local device variation. Let Vout be the output signal of interest, then the variance of Vout due to the i MOSFET is approximated by: th Vout)i ⎛ ∂ Vout⎞ ⎝∂ΔIds ⎠ i 2 = (EQ 2) Release Date Back Page 15 Close 15 Ids o σ2( ΔIdsi)
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