Thank you, Jerry (It is Jerry I assume?) It's much clearer now.|
There is another problem though. If I have a PWM output stage switching
at 1Mhz, the maximum resolution will be 40 if you use an 56807 running
at 40MIPS. Am I correct?
Telkom Development Laboratories
>>> "Johnson, Jerry" <> 02/13/02 04:31PM >>>
Using fractional math, if the input data sample is a FRACT16 number,
formula holds true. I believe you will want to deal with the sign of
sample separately, as to which output to enable.
From: Roelof Oelofsen [mailto:]
Sent: Tuesday, February 12, 2002 2:21 AM
Subject: [motoroladsp] Application brief BR1544/D Hi all,
In the motorola app. brief to design a class D amplifier, the author
states that to work out the PWM value register, the following formula
PWM Value = (Input Data Sample) x (PWM Modulus)
However, in the 56f80x user's manual, it is stated then whenever the
PWM Value is greater than or equal to the PWM Modulus, the output of
PWM will be 0 permanently (which makes sense).
When using above formula, the PWM value will always be more than the
PWM modulus except when the input data samples = 0. (The input data
samples is from a audio CODEC which have a 16 bit resolution).
I am reading the formula incorrectly. Can someone please shed more
on this subject for me.
Thank you in advance...
Telkom Development Laboratory
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