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EE5602_5_ARFaMT_AMP - RF/Microwave Transistor Types Bipolar...

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RF/Microwave Transistor Types Bipolar Junction Transistor Ge-BJT, Si-BJT, SiGe-BJT Heterojunction Bipolar Transistors (HBT) Field Effect Transistor (FET) Metal Insulator Semiconductor FET (MISFET) Metal Oxide Semiconductor FET (MOSFET) Junction FET (JFET) MEtal Semiconductor FET (MESFET) Hetero FET High Electron Mobility Transistor (HEMT) MOdulation Doped FET (MODFET) pseudomorphic HEMT (pHEMT)
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Small Signal RF Transistor Models Bipolar junction transistor: hybrid π Field effect transistor c π B E E C c μ r π g v m π v π r o c g s G S S D c g d c d s r g s g v m π v i r d s
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Large Signal RF BJT Model C d e C d c C j c C j e B E C R B B R E E I R I F α F I F α R I R R C C
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Large Signal RF FET Model C G D C G S G S D r S V G D V G S I D r D
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Packaging Effects at RF/Microwave c π B E E C c μ r π g v m π v π r o r E r B r C L E L B L C
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Small Signal Amplifier Design Transducer gain G T is a function of Γ L and Γ S . Power gain G P is a function of Γ L . Available gain G A is a function of Γ S . 2 22 2 2 21 2 2 1 1 1 1 L L S IN S T s s G Γ - Γ - × × Γ Γ - Γ - = 2 22 2 2 21 2 1 1 1 1 L L IN P s s G Γ - Γ - × × Γ - = 2 2 21 2 11 2 1 1 1 1 OUT S S A s s G Γ - × × Γ - Γ - =
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Stability Unconditional stability: | Γ IN | < 1 and | Γ OUT | < 1, for all passive source and load impedances. Conditional stability: | Γ IN | < 1 and | Γ OUT | < 1, for a certain range of source and load impedances. Also referred to as potentially unstable. Unconditional Stability For all Γ S and Γ L . Instability occur when the input or/and output port has a negative real part. This implies that | Γ IN | > 1 or | Γ OUT | > 1 and is frequency dependent. Define two types of stability, 1 1 1 1 11 21 12 22 ' 22 22 21 12 11 ' 11 F F S S OUT L L IN s s s s s s s s s s Γ - Γ + = = Γ Γ - Γ + = = Γ
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Stability Criteria A passive source and load reflection coefficient has a maximum magnitude equal to 1, | Γ S | < 1 and | Γ L | < 1. A magnitude of reflection coefficient for the input and output equal to 1 would be the boundary that separates stability from potential instability for a potentially unstable transistor. Equating the magnitude of the input and output reflection coefficient to 1 will give the boundary for the load and source reflection coefficient that separates stability from potential instability. 1 1 1 1 11 21 12 22 22 21 12 11 = Γ - Γ + = Γ - Γ + S S L L s s s s and s s s s
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Stability Circles Equating the magnitude of the input and output reflection coefficient to 1 results in circles in the load and source reflection coefficient planes. ( 29 ( 29 ( 29 ( 29 2 2 11 * * 22 11 2 2 11 21 12 2 2 11 21 12 2 2 11 * * 22 11 2 2 22 * * 11 22 2 2 22 21 12 2 2 22 21 12 2 2 22 * * 11 22 - - = - = - = - - - Γ - - = - = - = - - - Γ s s s C s s s R s s s s s s s s s C s s s R s s s s s s S S S L L L
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Test for Regions of Stability The stable and unstable region can be found by using a test impedance.
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