3.2.3 CMOS Recipe

TL;DR

MOSFETs are used to build circuits that process digitally encoded information, following rules for using n-channel (NFET) and p-channel (PFET) MOSFETs as voltage-controlled switches.

Transcript

Now that we have some sense about how MOSFETs function, let's use them to build circuits to process our digitally encoded information. We have two simple rules we'll use when building the circuits, which, if they're followed, will allow us to abstract the behavior of the MOSFET as a simple voltage-controlled switch. The first rule is that we'll onl... Read More

Key Insights

• 💁 MOSFETs can be used to build circuits for processing digitally encoded information.
• 🎊 NFETs are used in pulldown circuits and PFETs are used in pullup circuits.
• ⚡ The behavior of MOSFETs can be abstracted as voltage-controlled switches based on the gate-source voltage.
• 💦 CMOS devices exhibit high gain and can work reliably in different operating environments.

Questions & Answers

Q: What are the two rules for building circuits using MOSFETs?

The first rule is to use NFETs in pulldown circuits and PFETs in pullup circuits. The second rule is that the behavior of the MOSFET can be abstracted as a voltage-controlled switch.

Q: How does the gate voltage of an NFET switch affect its behavior?

If the gate voltage is a digital 0, the NFET switch will be off and not conducting. If the gate voltage is a digital 1, the NFET switch will be on and conducting.

Q: Why can't NFETs be used in pullup circuits or PFETs be used in pulldown circuits?

Using NFETs in pullup circuits or PFETs in pulldown circuits would result in degraded signaling levels and a loss of noise margins.

Q: How does a combinational inverter circuit work?

The combinational inverter circuit uses an NFET switch for the pulldown circuit and a PFET switch for the pullup circuit. The output is inverted based on the input signal.

Summary & Key Takeaways

• MOSFETs are used to build circuits for processing digitally encoded information.

• The behavior of MOSFETs can be abstracted as a simple voltage-controlled switch.

• NFETs are used in pulldown circuits and PFETs are used in pullup circuits.