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


MOSFETs and CMOS Inverter
Click here to download the full size of the above Circuit.

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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