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Reference Number: AA-01566 // Views: 32 // Created: 2018-12-10 16:39:45 // Last Updated: 2018-12-10 18:21:16
How to improve PWM from Digital Outs for fast switching frequencies (20kHz and more)

How to improve PWM from Digital Outs for fast switching frequencies (20kHz and more)

When transmitting PWM signals using long cables and/or when generating high speed switching patterns (20 kHz and more), we may have a detriment on the quality of the generated PWM. Problems that affect the quality of the PWM typically arise from the electrical interaction between the PWM signals and the physical channel (cable) through which they are transmitted: waveform reflection;impedance un-matching; cross taking noise, etc. 

The attached document covers different scenarios to reduce or avoid the detriment of transmitted digital signals in general.  The concepts and techniques covered in the document can be extrapolated to the specific case of PWM signals.

In the figure below, we see the improvement of a transmitted PWM pattern after putting a termination in the receiving end of the transmission cable (RC filter). There is a noticeable improvement in the quality of the PWM. The remaining small spikes in B)  seem to be  cross-taking of the signals that could be solved by shielding and twisting the cables that transmit the signals (not done for this specific example)

WP+CMOS-TTL+opal+RT_rev+1.0.pdf1.6 MbDownload File