Difference between revisions of "220-A3.3"

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We can also verify the transition frequency by running an AC analysis. For example, using <math>V_{GS}=0.5\mathm{V}</math> and <math>V_{DS}=1\mathm{V}</math>, we can plot the short-circuit current gain, as shown in Fig. 3. Thus, the transition frequency is the frequency when the short-circuit current gain drops to 1, or equivalently 0 dB.
  
 
== Activity: PMOS Transition Frequency ==
 
== Activity: PMOS Transition Frequency ==

Revision as of 23:05, 19 October 2020

Activity: MOS Frequency Response

  • Instructions: This activity is structured as a tutorial with an activity at the end. Should you have any questions, clarifications, or issues, please contact your instructor as soon as possible.
  • At the end of this activity, the student should be able to:
  1. Plot the frequency response of NMOS and PMOS transistors.

MOS Transition Frequency

Figure 1: The MOS transistor small signal model.

At high frequencies, the MOS gate-to-source capacitance, and the gate-to-drain capacitance, limits the MOSFET current gain at high frequencies, and thus, needs to be included in the two-port model, as shown in Fig. 1. The short-circuit current gain can be expressed as:

 

 

 

 

(1)

We then define the transition frequency, as the frequency when magnitude of the short-circuit current gain is equal to 1, or:

 

 

 

 

(2)

Thus, we get:

 

 

 

 

(3)

Assuming , we can plot the transition frequency of an NMOS transistor as a function of as shown in Fig. 2, using this SPICE file and Python script.

Figure 2: The NMOS Transition Frequency.
Figure 3: The Short-Circuit NMOS Current Gain.

We can also verify the transition frequency by running an AC analysis. For example, using and , we can plot the short-circuit current gain, as shown in Fig. 3. Thus, the transition frequency is the frequency when the short-circuit current gain drops to 1, or equivalently 0 dB.

Activity: PMOS Transition Frequency