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Re: [TCML] A Question about Solid State Drivers

That's right, Jim. The modulation width will correspond to the instantaneous
amplitude of the analogue input signal. My goal is to be able to reproduce
frequencies covering as much of the range of human hearing as possible, so
for the maximum auditory frequencies of about 20kHz, there are still 10
carrier cycles per signal cycle, which is quite good, I think. Taking into
account the Nyquist-Shanon sampling theorem, I will probably try to modulate
it at closer to 40kHz, but even if some of the top-end frequencies are lost,
I think it should sound quite good.

Again, does anyone have any experience sampling audio at these frequencies?


2009/12/7 jimlux <jimlux@xxxxxxxxxxxxx>

> Greg Morris wrote:
>> Hi Steve,
>> Thanks for the advice!
>> The reason I mentioned such a high "bandwidth" is because I intend to
>> music
>> modulate the coil. The coil will be nominally operating at around 200kHz,
>> but I want to be able to modulate it down to a 10% duty cycle, and up to a
>> 90% duty cycle (as well as 0% and 100%, of course, but not 95%, for
>> example). And so for a 10% duty cycle (or 90%) at 200kHz, the system needs
>> to be able to operate at a switching frequency of 10*200kHz = 2MHz.
> Are you modulating the duty cycle to change the "loudness"?  Your waveform
> is basically going to be a pulse train amplitude modulating a 200kHz carrier
> at, say, 440 Hz (for the note A).  The duty cycle you need to worry about is
> the audio modulation (e.g. say you use 1 millisecond bursts as "full power",
> you want to go down to say, 100 microseconds, which would give you a 10:1
> variation (comparable to your 10% to 100%).   Even at 100 microseconds,
> you've got 20 cycles of the 200 kHz carrier, which is plenty.
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Greg Weyrich Morris
VP External - Engineering Undergraduate Society
B.Sc. Electrical Engineering (Final Year)
University of New Brunswick
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