User:Mcginnsc/sandbox

Noise Reduction
In many cases noise found on a signal in a circuit is unwanted. When creating a circuit for whatever reason, one usually wants a true output as to what their circuit has accomplished. There are many different noise reduction techniques that may output an altered signal different from a theoretical output.
 * 1) Faraday cage - A Faraday cage is a good way to reduce the overall noise in a complete circuit. The Faraday Cage can be thought of as an enclosure that separates the complete circuit from outside power lines and any other signal that may alter the true signal. A Faraday cage will usually block out most electromagnetic and electrostatic noise.
 * 2) Capacitive coupling - A current through two resistors, or any other type of conductor, close to each other in a circuit can create unwanted capacitive coupling. If this happens an AC signal from one part of the circuit can be accidentally picked up in another part. The two resistors (conductors) act like a capacitor thus transferring AC signals. There may be other reasons for which capacitive coupling is wanted but then it wouldn't be thought of as electronic noise.
 * 3) Ground loops - When grounding a circuit, it is important to avoid ground loops. Ground loops occur when there is a voltage drop between the two ground potentials. Since ground is thought of as 0V, you should not want a voltage in a ground bus at any point. If this is the case, you do not have a true ground. A good way to fix this is to bring all your ground wires to the same potential in a ground bus.
 * 4) Shielding cables - In general, using shielded cables to protect your wires from unwanted noise frequencies in a sensitive circuit is good practice. A shielded wire can be thought of as a small Faraday cage for a specific wire as it uses a plastic or rubber enclosing the true wire. Just outside of the rubber/plastic covering is a conductive metal that intercepts any noise signal. Because we generally ground the conductive metal, the noise signal runs straight to ground before ever getting to the true wire. It is important to ground the shield at only one end to avoid a ground loop on the shield.
 * 5) Twisted pair wiring - Twisting wires very tightly together in a circuit will dramatically reduce electromagnetic noise. Twisting the wires decreases the loop size in which a magnetic field can run through to produce a current between the wires. Even if the wires are twisted very tightly, there may still be small loops somewhere between them, but because they are twisted the magnetic field going through the smaller loops induces a current flowing in opposite ways in each wire and thus cancelling them out.
 * 6) Notch filters - Notch filters or band-rejection filters are essential when eliminating a specific noise frequency.  For example, in most cases the power lines within a building run at 60 Hz. Sometimes your sensitive circuit will pick up this 60 Hz noise through some unwanted antenna (could be as simple as a wire in the circuit). Running your output through a notch filter at 60 Hz will amplify your true signal without amplifying the 60 Hz noise. So in a sense the noise will be lost at the output of the filter.