Patent ID: 7422366

Claim:
A method of extracting thermal characteristics in a silicon-on-insulator (SOI) power bipolar junction transistor (BJT) formed in a semiconductor substrate, the method comprising: providing a current mirror structure that includes a reference transistor and the power BJT; measuring the current I REF flowing through the reference transistor; measuring the current I OUT flowing through the power BJT; determining a mirror ratio MR that is equal to I OUT /I REF ; and utilizing the mirror ratio to determine the thermal characteristics, and wherein MR ⁡ ( MirrorRatio ) ≡ I OUT I REF ( 1 ) where I REF = β 1 · I B ⁢ ⁢ 1 + I B ⁢ ⁢ 1 + I B ⁢ ⁢ 2 ⁢ ⁢ and ⁢ ⁢ I OUT = β 2 · I B ⁢ ⁢ 2 . Assuming ⁢ ⁢ β = β 1 = β 2 , the ⁢ ⁢ mirror ⁢ ⁢ ratio ⁢ ⁢ becomes MR = I B ⁢ ⁢ 2 I B ⁢ ⁢ 1 · β β + 1 + I B ⁢ ⁢ 2 I B ⁢ ⁢ 1 , ( 2 ) where I B ⁢ ⁢ 2 I B ⁢ ⁢ 1 ≈ AR · ( 1 + Δ ⁢ ⁢ T T ) m · exp ⁡ [ ( qV BE kT ) · ( Δ ⁢ ⁢ T T 1 + Δ ⁢ ⁢ T T ) ] . ( 3 )