EE 332 Lecture 21 2019.pdf - EE 332 Devices and Circuits II Lecture#21 ©UWECE TC Chen BJT AMPLIFIERS/GAIN CALCULATION RI vi R1 R2 r gmvbe vo ro RC R3

EE 332 Lecture 21 2019.pdf - EE 332 Devices and Circuits II...

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5/7/2019 1 ©UWECE TC Chen EE 332: Devices and Circuits II Lecture #21 ©UWECE TC Chen BJT AMPLIFIERS/ GAIN CALCULATION v o v i R 2 R 1 R C R 3 r r o g m v be v be R I Terminal voltage gain: 𝐴 ?? ?? = 𝑣 ? 𝑣 ? = −𝑔 ? 𝑣 ?𝑒 × 𝑟 ? ∥ 𝑅 ? ∥ 𝑅 3 𝑣 ? And 𝑣 ?𝑒 = 𝑣 ? This yields, 𝐴 ?? ?? = 𝑣 ? 𝑣 ? = −𝑔 ? 𝑅 𝐿
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5/7/2019 2 ©UWECE TC Chen IMPORTANT LIMITS AND MODEL SIMPLIFICATIONS Assumptions: source resistance is small that 𝑅 𝐼 ≪ 𝑅 𝑖? Then the source voltage gain is 𝐴 ?? = 𝑣 ? 𝑣 𝑖 = −𝑔 ? 𝑣 𝑖 𝑣 𝑖 × 𝑅 𝑖? 𝑅 𝑖? + 𝑅 𝐼 × 𝑅 𝐿 = −𝑔 ? 𝑅 𝐿 = −𝑔 ? 𝑟 ? | 𝑅 ? |𝑅 3 In most design: 𝑟 ? ≫ 𝑅 ? and if 𝑅 3 ≫ 𝑅 ? , this yields, 𝐴 ?? ?? ≅ 𝐴 ?? ?? = −𝑔 ? 𝑅 ? = − 𝐼 ? 𝑉 𝑇 𝑅 ? = −40𝑉 𝑅? In common design, 𝑉 𝑅? = 𝑉 𝑅? = 𝑉 ?? and 𝑉 𝑅? = 1 3 𝑉 ?? ©UWECE TC Chen IMPORTANT LIMITS AND MODEL SIMPLIFICATIONS The estimate gain is: 𝐴 ?? ?? ≅ 𝐴 ?? ?? = −40𝑉 𝑅? = −13.3𝑉 ?? and rounded to − 10𝑉 ?? Small signal limits for the CE amplifier 𝑣 ?𝑒 = 𝑣 𝑖 × 𝑟 𝜋 ∥ 𝑅 1 ∥ 𝑅 2 𝑟 𝜋 ∥ 𝑅 1 ∥ 𝑅 2 + 𝑅 𝐼 Small signal model requires 𝑣 ?𝑒 ≤ 0.005 V , then 𝑣 𝑖 × 𝑟 𝜋 ∥ 𝑅 1 ∥ 𝑅 2 𝑟 𝜋 ∥ 𝑅 1 ∥ 𝑅 2 + 𝑅 𝐼 ≤ 0.005 𝑣 𝑖 ≤ 0.005 × 𝑟 𝜋 ∥ 𝑅 1 ∥ 𝑅 2 𝑟 𝜋 ∥ 𝑅 1 ∥ 𝑅 2 + 𝑅 𝐼 = 0.005 × 1 + 𝑅
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