Introduction:
In a MOSFET follower stage, the output impedance is an important parameter that determines the ability of the stage to drive a load. The output impedance represents the resistance seen by the load, and a lower output impedance indicates a better ability to drive the load without significant voltage drop. In this context, we will discuss the effect of increasing the transconductance of a MOSFET on the output impedance of the follower stage.

Explanation:
When the transconductance of a MOSFET increases, it implies that the device can provide a higher output current for a given input voltage. This increased transconductance is typically achieved by increasing the gate-source voltage or biasing conditions.

Effect on Output Impedance:
When the transconductance of the MOSFET increases, the output impedance of the follower stage decreases. This can be understood by considering the following points:

1. Output Impedance Definition: Output impedance is the resistance seen by the load when an AC signal is applied. It is determined by the internal impedance of the source and the output resistance of the stage.

2. Internal Impedance: The internal impedance of the source is typically negligible compared to the output resistance of the stage. Therefore, the output impedance is primarily determined by the stage's output resistance.

3. Effect of Transconductance: The transconductance of a MOSFET is a measure of the device's ability to convert an input voltage into an output current. A higher transconductance implies that the MOSFET can deliver a larger output current for a given input voltage.

4. Output Resistance: The output resistance of a MOSFET follower stage is mainly determined by the drain-source resistance (Rds) of the MOSFET. A lower drain-source resistance results in a lower output resistance.

5. Transconductance and Drain-Source Resistance: The transconductance of a MOSFET is inversely proportional to its drain-source resistance. Therefore, as the transconductance increases, the drain-source resistance decreases, leading to a lower output resistance.

6. Output Impedance Decreases: Since the output impedance is primarily determined by the output resistance, a decrease in the output resistance results in a lower output impedance. Hence, when the transconductance of a MOSFET increases, the output impedance of the follower stage decreases.

Conclusion:
In summary, neglecting channel length modulation, when the transconductance of a MOSFET increases, the output impedance of the follower stage decreases. This is because the higher transconductance leads to a lower drain-source resistance, which in turn decreases the output resistance and improves the stage's ability to drive a load.