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ElectronicsI_L13

# ElectronicsI_L13 - Lecture 13 Example Using this circuit we...

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Lecture 13

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Example • Using this circuit, we want to establish a drain current of 0.5mA • The MOSFET has these qualities: –V t =1V –K n ’W/L=1mA/V 2 – Channel length modulation is ignored •V DD =15V
Example • As a rule of thumb, we will design the circuit such that 1/3 of the voltage drops across each component, thus evening out the voltage drops • This means that V D =10V and V S =5V • We can calculate the required resistances from this: Ω = = = k mA I V V R D D DD D 10 5 . 0 10 15 Ω = = = k mA R V R S S S 10 5 . 0 5

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Example • We now want to find the voltage to apply to the gate to get 0.5mA of drain current. • First calculate the overdrive voltage: • The gate source voltage is: • With the source biased at +5V, the voltage to be applied to the gate is: • We want to get this bias from a voltage divider using large valued resistors. • We can choose: –R G1 =8M –R G2 =7M 2 2 1 OV n D V L W k I = V V V V mA mA OV OV 1 / 1 2 1 5 . 0 2 2 = = V V V V t OV GS 2 = + = V V V V S GS G 7 5 2 = + = + =
• The or gate was two gates in parallel: Thus either input would generate a response • The and gate requires both inputs to be high to switch. ..

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ElectronicsI_L13 - Lecture 13 Example Using this circuit we...

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