How does a low pass filter demodulate a pulse width modulated signal? - design of pulse oximeters webster rapidshare
I am stuck at home, away from the library of science: (
I need a good explanation or a Web site explaining how to take the pulse width modulated signal (original signal varies in amplitude and frequency) - and demodulated with a low pass.
It was proposed to use an operational amplifier in my filter design. If you have an idea why someone wants to put operational amplifiers in a filter, I wonder, too!
Thanks
Friday, December 11, 2009
Design Of Pulse Oximeters Webster Rapidshare How Does A Low Pass Filter Demodulate A Pulse Width Modulated Signal?
2 comments:
I agree with the previous answer. The filter allows to pass the modulated signal to the amplifier, but the company demanded in 20dB/decade above the resonant frequency of the filter falls.
The amplifier uses feedback to improve the filtering and amplify the desired signal with the power supply. Passive devices do not provide amplification.
PWM modulation at a certain frequency. A modulated signal has a lower frequency than the PWM carrier. Therefore, if you have a low pass filter that eliminates the PWM carrier, but allowed to pass the low frequencies to obtain the demodulated signal situation.
Why an amplifier? An operational amplifier is an active element that can make a better filter that only passive components.
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