# MOSFETs and CMOS Inverter

Posted on Feb 7, 2014

Using measured threshold voltage and Ids-Vds curves, we can then check how well first-order MOSFET theory holds up in real devices and get a practical feel of the limitation of first-order theoretical MOSFET equation. The MOSFETs we will use in this experiment are from ALD1105, an IC containing two n-MOSFETs and two p-MOSFETs. A circuit symbol des

cription of the two pairs of transistors from the data sheet is shown below in figure 1. Note each transistor has four terminals: drain (D), source (S), gate (G), and substrate, which is called body (B) in our text. As we learned in class, all the n-MOSFETs on an IC share the same p-type body, which needs to be tied to the lowest voltage in a system to keep all the source/drain to body PN junctions zero or reverse biased. Similarly, all the p-MOSFETs on an IC share the same n-type body, which needs to be tied to the highest voltage in a system to keep all the source/drain to body PN junctions zero or reverse biased. A MOSFET is a natural voltage-controlled switch, as illustrated in figure 3. A high gate voltage turns on the MOSFET channel, allowing current to flow between drain and source, thereby turning a load, which can be a LED, a speaker or a fan. The amount of current the MOSFET can provide depends on the transistor physical properties such as width, length, oxide thickness, etc. , the gate voltage, and the load. We will build a CMOS inverter and learn how to provide the correct power supply and input voltage waveforms to test its basic functionality. For a given supply VDD, your voltage low should be zero, and voltage high should be VDD. By default, the function generator gives an output that varies from -VPP/2 to +VPP/2, with VPP being peak-to-peak voltage. For a square wave, the voltage low is -VPP/2, voltage high...

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