L
Lasse Langwadt Christense
Guest
Den lřrdag den 31. maj 2014 01.55.03 UTC+2 skrev Joerg:
all deltasigmas have "issue" when you get very close to the rails, though I'd think pwm also have a similar problem
I just threw that together to show deltasigma, I'd expect an AD7400 to
perform better
I used to work with a guy that two mouses, one for each hand. He claimed it was very quick to get used to switching between them
-Lasse
Lasse Langwadt Christensen wrote:
Den fredag den 30. maj 2014 19.18.22 UTC+2 skrev Joerg:
Lasse Langwadt Christensen wrote:
Den fredag den 30. maj 2014 18.34.37 UTC+2 skrev Joerg:
Lasse Langwadt Christensen wrote:
Den fredag den 30. maj 2014 16.15.46 UTC+2 skrev Joerg:
John Larkin wrote:
On Thu, 29 May 2014 18:07:45 -0700, Joerg <invalid@invalid.invalid> wrote:
John Larkin wrote:
On Thu, 29 May 2014 14:20:26 -0700, Joerg <invalid@invalid.invalid
wrote:
Folks,
Does anyone know an IC that can turn a control voltage into PWM and can
handle PWM frequencies in the 50-1000kHz range? Similar to a class D
driver but has to go down to DC. The changes in control would be
restricted to the audio spectrum below 15kHz.
The LTC6992 does this nicely but isn't precise enough. Same with
555-style timers or switcher chips. I am looking for better 1% and
ideally a lot better, including nonlinearity, drift, warts and all. A uC
is not suitable either because it should be simple and I need very fine
control granularity, down to around 0.1%.
Can't use short-lived consumer chips for radios and TV sets and such.
How about a sawtooth or triangle waveform and a comparator. Close a
feedback loop around that, with a PWM to DC converter; the PWM-DC part
can be made very linear.
That's what I wanted to avoid for real estate reasons. But if I hafta
I'll do it.
If you want 0.1% accuracy, you might be able to do it open-loop, with a very
linear ramp, but it will be hard at that frequency. If you only want 0.1%
resolution ("granularity"?) it's not so bad.
Can you use delta-sigma? There are some integrated d-s modulators around.
I could but then I'd have to build a one-shot that stretches the pulses
into a very precise length and that's almost the same kind of challenge
as building my own PWM generator (needs too much space).
why would you need a one-shot? the output is clocked
something like the AD7401, if you want to be sure a flipflop on the output
It's possible but when assuming a master clock of 20MHz going in and I'd
want, say, a 1k granularity that would result in an effective PWM of
only 20kHz. Unless I am understanding something wrong in the datasheet.
with DS is hard to talk about pwm frequency, it has noise shaping so the
switching noise gets pushed to higher frequencies. i.e if you are exactly midrange the "pwm frequency" would be 10MHz
with a brick wall reconstructions filter you would normally gain 3dB every
time you double the sampling frequency, with a second order deltasigma you
gain ~15dB, first order ~9dB
http://www.analog.com/static/imported-files/data_sheets/AD7401.pdf
What I'd essentially need is a class D audio modulator but without the
DC cut-off. Unfortunately that's as rare as it is on audio CODECs where
only a few such as the AD1939 can go down to DC without onerous offset
issues or huge drift.
if you can live with the higher switching frequency I think deltasigma
would do that
I can't live with a switching frequency that gets much past a MHz in
certain areas. It will cause large losses in the attached power
electronics. I'd like the PWM to be at least somewhat constant in
frequency. It isn't critical though, if it varies even 50% that would be
ok. But not a lot more.
so clock it at 2MHz, I still think it'll be close
It can be done this way, although the output in the simulation isn't
very clean around the min/max values of the drive signal.
all deltasigmas have "issue" when you get very close to the rails, though I'd think pwm also have a similar problem
[simulation file]
I just threw that together to show deltasigma, I'd expect an AD7400 to
perform better
Just came back from a gnarly mountain bike ride. Got a blister on the
right palm from all the handlebar wrestling. That's a pain when the
computer mouse is on the right, ouch, ouch ...
I used to work with a guy that two mouses, one for each hand. He claimed it was very quick to get used to switching between them
-Lasse