What you are looking for is a Class E amplifier.

The essence of the design is to use a switching transistor to generate a
square wave output and then shape the output using an RLC circuit.  The math
is fun... honest !!!

Look at the following web sites for more information:

        http://argesim.tuwien.ac.at/comparisons/c3/c3.html
        http://www.its.caltech.edu/~mmic/reshpubindex/davisAmp/class-e.htm
        http://www.its.caltech.edu/~mmic/reshpubindex/papers/ClassE.pdf

There was an article on this with in the past year in one of the engineering
publications (IEEE Spectrum, I think) which highlighted the benefits of
Class E amplifiers in laptop computers where energy management (battery
life) was a critical issue.


Tom

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of roger
Sent: Sunday, 02 January 2000 11:09
To: PICLIST@MITVMA.MIT.EDU
Subject: digital sound: part deux


excuse me for failing to mention i understand a transistor as a
switch. any further discussion of analog electronics will be over my
head.

now, if you are still with me, what i want is a direct digital sound.
chirp the processor out at the desired frequency(ies) direct to the
sound as perceived.

a square wave is produced by the processor. i can count until i'm blue
but the output of any logic chip is a square wave. (no conversion
please.) a square wave makes a buzz.

a tone or note, (and forgive my misuse of terminology), is a complex
form made of several different frequencies, and presumably different
wave shapes.

an analog speaker is used to create an audible note, pleasing to the
ear. it is controlled through a magnet which switches on/off. (perhaps
the secret is in its switching partially on, partially off, but i
think that is volume).

by switching a magnet attached to a speaker on/off at a particular
frequency i will have a tone, but a buzzing tone. to make it more
pleasing i have to ramp the magnet up and ramp it down at some sub
frequency, is that correct?

using digital it seems that i am stuck here. if i use multiple loops
to control the various sub frequencies then, it seems to me, they will
add and create some other, lower frequency.

what i had begun to think of was some sort of direct ear canal implant
using MEMS technology that might use a hammer striking directly onto a
membrane next to the ear drum. or a hammer striking tuned rods next to
the eardrum. digital to digital until inside the earcanal where the
analog conversion takes place without any outside ambient noise to
interfere. any thoughts on this?