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Passive filter cleans up power-line communications

Passive filter cleans up power-line communications

igital-clock-period jitter is the variation in the period of a clock cycle compared with a nominal (average of many cycles) clock period.To accurately measure period jitter using an oscilloscope, you must subtract the oscilloscope jitter from the measured jitter.
They are 100-Hz to 20-kHz passband filters; the communication frequency is 5 kHz. The difference between the two filters lies in the input impedance. The input filter must present a 2.2-kÙ impedance, and the output filter must have a 30Ù impedance. The circuit also needs a solid-state relay, the PVT412 from International Rectifier (www.irf.com) to isolate the output filter. When the circuit is active, the relay connects the output filter to the line. A microcontroller controls the relay to implement the signal-transmission and -reception protocols. ACTIVE_TRANS, RELAY, and TX are the microcontroller pins that control transmission, and RX is the pin that controls reception. Figure 2 shows waveforms before (Figure 2a) and after (Figure 2b) insertion of the input filter. Figure 3 shows waveforms before (Figure 3a) and after (Figure 3b) insertion of the output filter.

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