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Noise pick up and controller
hi, for our project msp430g2211 controller is used.. in that noise is picked up in input to the comparator... for that we used capacitor across the controller port pin with respect to ground... noise is arrested..... but putting of capacitor to the port pin takes high current at initial state.. is it really? then how to arrest noise ..,please give solution...... and also i have one more doubt.. noise is highly pick-up in the our transistor amplifier stage ... what are the remedies to take care to prevent the noise.... noise reduced if hand or metal piece bring to nearest...
Hi Karthick,
If the port pin that the capacitor is located on tries to initialize itself as a logic-high output then it will have to charge the capacitor which likely explains the high current you're observing. Keep in mind that the voltage can not instantaneously change on a capacitor so if the processor tries to quickly take the port pin from a "0" to a "1" then the capacitor may draw significant current until it's charged. The higher the capacitance value the larger the current will be.
You could consider adding some series resistance between the capacitor to GND and the port pin input. This would limit the current that could flow out of the controller into the capacitor but should not affect the comparator functionality because once the controller is updated to use that port pin as the comparator the input impedance should be high and there should be little error across the resistor. Try a 1k resistor.
Please provide a schematic for your amplifier circuit and we can suggest some noise minimizing techniques. Is your circuit on a dedicated printed-circuit-board or is it on a breadboard?
Regards,Collin WellsPrecision Linear Applications
Thank you .. Mr. Collin Wells
p1.0 is comparator reference....
p1.1 is comparator input from amplifier circuit...
p1.2 is comparator output and which is connected to the other port.(p1.3).. and this terminal is connected to ground through capacitor(10nf)...
i tried it with pcb .. i make copper pouring also..... plaese suggest me what to do ... and also if any metal plate is bring nearer to amplisier circiut the noise gets reduced
.
Hello,
Placing a capacitor directly on the output of a comparator is not recommended and will not serve the purpose your looking for. To help reduce some noise in this circuit, please place a capacitor in parallel with R2, and one between "COMP" and GND.
If your comparator output is toggling due to noise or glitches in your "COMP" signal as it crosses the reference voltage then consider using some positive feedback to create hysteresis in your comparator output. Here are few links for examples on creating hysteresis in comparators:
http://www.eetimes.com/design/automotive-design/4010061/Signal-Chain-Basics-Part-17--Hysteresis-Understanding-more-about-the-analog-voltage-comparator
http://www.edn.com/article/484129-Adding_Hysteresis_to_comparators.php
The links above were quickly found and there are a multitude of other articles and app notes providing the same information.
Regards,Collin WellsPrecision Linear
I realized I did not address your "metal shield" questions.
If your circuit is suffering from noise pick-up from extrinsic (external) noise sources then placing a shield around your circuit is one method that can be used to reduce the noise. Please do an internet search for "Faraday Cage" to learn more about this type of protection method.
Other methods to help reduce these effects are to ensure proper power-supply decoupling, proper power-supply and GND routing on your PCB, and be sure to use a solid copper pour GND plane.