Dec 20 2006
Awful design
With time running out and with one fixable fatal flaw in my circuit, I have decided to solve the problem with a 1nF MOS capacitor. (There’s another fatal flaw in my circuit but there’s nothing I can do about it so I’ll just let it be.)
Yes, you heard me right, I said 1 nanofarad. I didn’t mean 1 femtofarad and I didn’t mean 1 picofarad. I am not joking. I am putting a 1 nF MOS capacitor on my chip. I’m talking nano as in 10E-9. Forget that the iPod Nano is marketed as a small device. 1nF is freakin huge for an on-chip capacitor. It looks like it will be several times larger than the rest of my circuit.
So what exactly is a MOS capacitor? A MOS capacitor is pretty much the picture you see at the top of this page, except that the source and the drain (the dark green areas on the left and the right) are tied to ground. MOS stands for Metal Oxide Semiconductor. In the diagram above, the red block is the metal in a MOS capacitor even though it is usually made of doped polysilicon, the light gray strip is oxide which acts as the capacitor’s dielectric, and the stuff below the oxide is a semiconductor. Hence it is called a MOS capacitor.