erich@inmet.inmet.com (11/20/90)
Given some input signal which passes through a high speed switch
and then through a low pass filter.
in ______./ .______/\/\/\_______ out
switch res |
| |cap
| |
|
____
///
If the switch is turned on and off by some control line at a constant
frequency Fsw.
and Fsw >> Fin (input frequency)
and F-3db of Low Pass Filter > Fin
Will Output Signal = Input signal x Duty cycle of control line
with no distortion of the output signal relative to the input
except for attenuation?
Any comments on this type of system would be helpful.
I would simulate it on Pspice but no longer have a copy.
Thanks much...
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Internet: erich@inmet.inmet.com
UUCP: uunet!inmet!erichpgc@csadfa.cs.adfa.oz.au (Phil Clark) (11/21/90)
In article <17100009@inmet>, erich@inmet.inmet.com writes: > Given some input signal which passes through a high speed switch > and then through a low pass filter. > > in ______./ .______/\/\/\_______ out > switch res | > | |cap > | | > | > ____ > /// > If the switch is turned on and off by some control line at a constant > frequency Fsw. > Any comments on this type of system would be helpful. > I would simulate it on Pspice but no longer have a copy. I would suggest that you have a look at National Semiconductor data books for chip types MF4 to MF10 - various types of switched capacitor filters. Phil Clark Department of Computer Science, Phone: (VK1PC) Australian Defence Force Academy, +61 6 268 8157 Email: Northcott Drive, Campbell, Fax: pgc@csadfa.cs.adfa.oz.au Canberra, Australia, 2600. +61 6 268 8581
jgk@osc.COM (Joe Keane) (11/22/90)
In article <17100009@inmet> erich@inmet.inmet.com writes: > in ______./ .______/\/\/\_______ out > switch res | > | |cap > | | > | > ____ > /// >Will Output Signal = Input signal x Duty cycle of control line > with no distortion of the output signal relative to the input > except for attenuation? Almost. The problem is that you're not really switching voltages, since when the switch is off the filter input is disconnected rather than grounded. The output will just follow the input. If you switch the filter input to ground during this time, the circuit will behave as you expect. It's easier to work with current switching and filtering, since when you open the switch you know you'll get zero current. In this case your energy storage device will be an inductor rather than a capacitor. This is how most switching power supplies work.