Analyze MOSFET saturation behavior with practical engineering outputs. Calculate current, conductance, resistance, and gain instantly. Ideal for device modeling, design reviews, labs, and revision.
Overdrive voltage: VOV = VGS − VTH
Width to length ratio: W/L = Width ÷ Length
Effective beta: β = k′ × (W/L)
Ideal saturation current: ID0 = 0.5 × β × (VOV)²
Drain current with channel length modulation: ID = ID0 × (1 + λVDS)
Transconductance in saturation: gm = 2ID ÷ VOV
Output conductance: gds = λ × ID
Output resistance: ro = 1 ÷ gds
Early voltage: VA = 1 ÷ λ
Intrinsic gain: Av ≈ gm × ro
These equations are most accurate for long channel style saturation analysis. The page also flags cutoff and linear operation.
| Case | k′ (uA/V²) | W (um) | L (um) | VGS (V) | VTH (V) | λ (1/V) | VDS (V) | Region | ID (uA) | ro (kOhm) |
|---|---|---|---|---|---|---|---|---|---|---|
| Case 1 | 200 | 20 | 1 | 2.4 | 0.8 | 0.03 | 5.0 | Saturation | 5888.00 | 5.66 |
| Case 2 | 150 | 10 | 1 | 1.8 | 0.7 | 0.02 | 3.3 | Saturation | 998.25 | 50.09 |
| Case 3 | 180 | 8 | 2 | 1.5 | 0.9 | 0.01 | 0.4 | Triode | 115.20 | 11.57 |
Channel length modulation changes the drain current of a MOSFET in saturation. The current does not stay perfectly flat as VDS rises. Real devices show a small slope in the output curve. That slope affects gain, resistance, and bias stability. Engineers must include this effect when estimating analog behavior.
This calculator estimates the main quantities used in transistor analysis. It starts with threshold and overdrive voltage. It then builds the effective beta value from process strength and transistor geometry. After that, it calculates ideal saturation current and corrected current with channel length modulation. It also reports gm, gds, output resistance, and intrinsic gain.
A larger W/L ratio increases channel strength. A higher overdrive voltage increases drain current strongly. A larger lambda value reduces output resistance. Higher VDS raises current when the device is in saturation. These relationships are useful in analog amplifiers, current mirrors, active loads, and bias networks.
The operating region is important. In cutoff, current is nearly zero. In the linear region, the device acts more like a controlled resistor. In saturation, the classic channel length modulation model becomes most useful. The calculator highlights that region so you can decide whether the output resistance and intrinsic gain are appropriate for design work.
Students use this model in device courses and lab reports. Circuit designers use it when checking hand calculations before simulation. It also helps when comparing long channel assumptions with practical transistor behavior. A quick estimate of output resistance can explain gain loss in common source amplifiers or current mismatch in mirrors.
Use smaller lambda values for longer effective channels. Increase channel length when higher output resistance is required. Check that VDS stays above VOV for saturation operation. Compare hand results with simulator plots for validation. This creates better intuition and supports faster engineering decisions.
It is the increase in MOSFET drain current caused by higher VDS in saturation. The effective channel becomes slightly shorter, so current rises instead of staying constant.
Output resistance affects voltage gain, current mirror accuracy, and bias quality. A higher output resistance usually improves analog performance in active loads and amplifier stages.
This model is most useful when the MOSFET is in saturation. That condition normally requires VGS above threshold and VDS greater than or equal to overdrive voltage.
Lambda is the channel length modulation coefficient. It shows how strongly drain current changes with VDS. Larger values mean lower output resistance and stronger current variation.
Yes. The calculator identifies linear operation and estimates current there. Still, the detailed channel length modulation interpretation is mainly intended for saturation analysis.
Early voltage is the inverse of lambda. A higher Early voltage indicates weaker channel length modulation and a flatter drain current curve in saturation.
gm·ro gives an intrinsic gain estimate. It helps you judge how much gain a transistor can support before external resistive loading and other circuit limits are included.
Hand calculations are useful for speed and insight. Final engineering work should still compare these estimates with device models, simulation results, and measured data.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.