Checkpoint LAB USB-RS232 Manuel d'utilisateur télécharger pdf (Page 16)

NOISE IMMUNITY

A SOLUTION: LOWPASS FILTER

Remove high frequency noise. Simple RC low pass filter

(left) or active circuit (right) for improved isolation, gain and

current driving capability. May want to add software

sampling to remove glitches or switch bounce.

NOISE IMMUNITY

CMOS AND NOISE

• 1 uA input? Not sure? Get the spec sheet!...

• Draw the equivalent circuit for each internal pin.

That is, CMOS versus TTL input impedance, output is

pull-up or pull-down circuit, current limiting resistor

value.

• CMOS inputs have very high input impedance

which is good for low power consumption but

susceptible to sudden discharge or misuse when

connecting to the outside world.

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Checkpoint LAB USB-RS232 Manuel d'utilisateur Page 16