Large Signal Behavior

Introduction of Field Effect Transistors Distinction between a BJT and FET Junction Field Effect Transistor (JFET) N Channel JFET Summary of JFET Operation Mutual or Transfer Characteristic of n-channel JFET Amplification Factor 𝝁 Definition of Parameters p-Channel JFET

Introduction of Metal Oxide Semiconductor Field Effect Transistor - Mosfet Terminals in MOSFET Physical structure of MOSFET MOSFET Working Operation Summary of Operation MOSFET - N Type MOSFET Operation How does Drain current flow MOSFET operation More about Threshold Voltage Current vs Voltage Characteristics - Derivation Non Ideal Current -Voltage Effects or Second Order Effects Short Channel Effects MOSFET Device Capacitances MOSFET Large and Small signal Model pMOSFET Small SIgnal Model To use MOSFET device as a Capacitor nMOSFET as Capacitor- Working

Single Stage Amplifiers Common Source CS Stage with Diode-Connected Load Circuit to measure the Equivalent Resistance Common Drain Stage or Source Follower Common Gate Amplifier Large Signal Behavior Calculation of Input Resistance of a Common Gate Stage

Inverter with Enhancement n- Type MOS as Load Inverter with Linear Enhancement Type Load

Large Signal Behavior

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Large Signal Behavior

Assume the input voltage Vin is reduced from a large positive value.
Assume that the channel length modulation effect is 0

If the input voltage Vin ≥ Vb - Vth, the MOS transistor is in OFF condition.

∴ Vout = VDD

$I_D=\frac12\mu_nC_{OX}\frac WL\left(V_b-V_{in}-V_{th}\right)^2$

For smaller values of Vin, and if the MOS transistor is operating in the Saturation region.

The output voltage Vout when the MOS transistor is operating in the saturation region is given by:

$V_{out}=V_{DD}-\frac12\mu_nC_{OX}\frac WL\left(V_B-V_{in}-V_{th}\right)^2R_D$

As Vin decreases, Vout also decreases, thus driving the MOS Transistor into triode region if

$V_{DD}-\frac12\mu_nC_{OX}\frac WL\left(V_b-V_{in}-V_{th}\right)^2R_D=V_b-V_{th}$

Let us calculate the small signal gain and is given by

$\frac{\partial V_{out}}{\partial V_{in}}=-\mu_nC_{ox}\frac WL\left(V_b-V_{in}V_{th}\right)\left(-1-\frac{\partial V_{th}}{\partial V_{in}}\right)R_D$

Also we know,

$\partial V_{th}/\partial V_{in}=\partial V_{sb}=\eta$

The small signal gain can be re written in terms of transconductance and body effect as:

$\frac{\partial V_{out}}{\partial V_{in}}=\mu_nC_{ox}\frac WLR_D\left(V_b-V_{in}-V_{th}\right)\left(1+\eta\right)\\=g_m\left(1+\eta\right)R_D$

Note:

The Voltage Gain is Positive
The body effect increases the transconductance of the stage
To increase the gain of a common Gate amplifier, do the following:
- Widen the MOS transistor so that gm increases
- Increase RD

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Large Signal Behavior

Field Effect Transistors

Field Effect Transistors

Metal Oxide Semiconductor Field Effect Transistor - Mosfet

Metal Oxide Semiconductor Field Effect Transistor - Mosfet

Amplifiers

Amplifiers

Inverters

Inverters

Large Signal Behavior