question stringlengths 23 136 | answer stringlengths 294 1.09k | image_path dict |
|---|---|---|
If we double the length and width of a MOSFET, what happens to its intrinsic gain? | The intrinsic gain is `Av,int = gm ro`.
If both `W` and `L` are doubled while the overdrive voltage is kept constant, `W/L` is unchanged, so `gm` is approximately unchanged. The drain current is also approximately unchanged, while `ro = 1/(lambda ID)` increases because `lambda` decreases as `L` increases. Thus `ro` ap... | null |
Student A says the transconductance of a MOSFET goes up as the overdrive voltage increases. Student B says it goes down. Who is correct? | Both statements can be true, depending on what is held fixed.
For a long-channel MOSFET in saturation,
`gm = mu Cox (W/L) Vov = 2 ID / Vov`.
If `W/L` is fixed and `Vov` is increased, then `ID` rises as `Vov^2` and `gm` increases linearly with `Vov`; Student A is correct under this condition. If instead `ID` is fixed... | null |
Is the small-signal model of a PMOS device identical to that of an NMOS device? | Yes, the small-signal model has the same form after using consistent voltage and current polarities.
A PMOS has `gm`, `gmb`, `ro`, and terminal capacitances analogous to an NMOS. The controlled source direction and sign conventions are reversed if the same absolute node-voltage directions are used, but with source-ref... | null |
Sketch IX versus VX in the circuit in Figure 1. | The transistor is diode-connected with its gate and drain tied to `VX`, source at ground. For `VX <= VTH`, the device is off and `IX` is approximately zero.
For `VX > VTH`, the device operates in saturation because `VDS = VGS = VX`, so
`IX ~= (1/2) mu Cox (W/L) (VX - VTH)^2`
ignoring channel-length modulation. The s... | {
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Sketch IX versus VX in the circuit of Figure 2. | In Figure 2, `VX` is applied to the gate, the source is grounded, and the drain is held at `1 V`. Thus `VGS = VX` and `VDS = 1 V`.
For `VX <= VTH`, the transistor is off and `IX ~= 0`.
For `VTH < VX < VTH + 1 V`, the condition `VDS >= VGS - VTH` is satisfied, so the device is in saturation and
`IX ~= (1/2) mu_n Cox ... | {
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Can the device shown in Figure 3 act as a current source? | No. The device is diode-connected, so it presents a low small-signal resistance of roughly `1/gm` rather than a high output resistance.
A good current source should maintain nearly constant current while its terminal voltage changes. Here the current is strongly set by the terminal voltage through the diode-connected ... | {
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Analyze the circuit shown in Figure 4. | "Figure 4 is a PMOS common-source stage with source degeneration. The source is connected to `VDD` t(...TRUNCATED) | {"bytes":"iVBORw0KGgoAAAANSUhEUgAABT4AAANyCAYAAABL5NSMAAAEDmlDQ1BrQ0dDb2xvclNwYWNlR2VuZXJpY1JHQgAAOI(...TRUNCATED) |
Analyze the circuit shown in Figure 5. | "Figure 5 is a source follower. The input is applied to the gate, the output is at the source, and `(...TRUNCATED) | {"bytes":"iVBORw0KGgoAAAANSUhEUgAABEwAAANSCAYAAAB/elvfAAAEDmlDQ1BrQ0dDb2xvclNwYWNlR2VuZXJpY1JHQgAAOI(...TRUNCATED) |
Analyze the circuit shown in Figure 6. | "In Figure 6, `Vin` is applied to the source of `M1`, the gate is tied to a dc bias at `VDD` and is (...TRUNCATED) | {"bytes":"iVBORw0KGgoAAAANSUhEUgAABD4AAANQCAYAAADADq9xAAAEDmlDQ1BrQ0dDb2xvclNwYWNlR2VuZXJpY1JHQgAAOI(...TRUNCATED) |
Analyze the circuit shown in Figure 7. | "In Figure 7, `Vin` is coupled through `C1` to the source node of `M1`, but that same source node is(...TRUNCATED) | {"bytes":"iVBORw0KGgoAAAANSUhEUgAABRYAAARWCAYAAABO9O4GAAAEDmlDQ1BrQ0dDb2xvclNwYWNlR2VuZXJpY1JHQgAAOI(...TRUNCATED) |
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