More on Schematics | Cypress Semiconductor
More on Schematics
April 30, 2011
Earlier I said that a schematic is a solution, not a definition. Actually a schematic is a representation of an idea at a particular time using specific time appropriate components. . It conveys the implementation of an idea with time and situation resources. Below a schematic for a high pass filter from Sallen and Key’s famous 1955 paper.
60 years ago if I went into a customer they might ask “can you do this”? Now there are few you old guys or audio freaks around that are comfortable with this design. It is made with a vacuum tube. I call them gas FETS. They are what people used before transistors. Transistors are made of sand (dirt) and before dirt was invented this is what they had to use. While I am not older than dirt, dirt was a pretty new concept when I was born so I do have a working knowledge of these little puppies. Below is the same filter as a block diagram. I am sure this will make sense long after whatever technology we are presently using is gone.
Note the S&K did not express the idea as an op amp. Just as a buffer with gain.
Sallen & Key’s article has to be one of the best ever written. I would attach a copy but believe it or not it is still under copy write. It really bothers me that I cannot get access to this paper without paying a fee to the IEEE. Especially since that paper was the result of work financed by a government grant using tax payer (my) money. If you don't want a copy, don’t e-mail me, and I won’t send you a copy.