ptonsparky
Tom
- Occupation
- EC - retired
Can someone give me an expample of a "single-ended input signal" and a "differential input signal"?
Single ended input
- Thread starter ptonsparky
- Start date
- Status
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
080419-1710 EST USA
A single ended input would use common as a reference for the signal.
For example: an amplifier input would be single ended if one signal wire, often times this is also the shield, is connected to the chassis of the amplifier, and this may be ultimately tied to physical ground or some other chassis. The other side of the signal is connected to the amplifier input. Note effectively we are amplifing the signal between common and the single input wire at the amplifier input. This is a difference measurement, but I do not really want to use that term here.
If at the source of the signal, a microphone for example, the common is connected to another common that thru some other path connects to the common of the amplifier, and suppose these are earth ground, then it is not unusual for there to be differences in voltage between different ground points. A voltage in this common path between the microphone and the amplifier adds to the desired signal and produces an unwanted addition to the signal. In this case probably 60 Hz hum. No solution here except to make sure the microphone common is floated, insulated from anything else.
A differential signal has neither signal line connected to common. In the case of the microphone the coil is connected between two wires neither of which is connected to common, and the shield is a separate wire. At the destination, amplifer input, the circuitry measures the difference between the two signal lines. If there is a noise signal in the common path, then if evenly coupled to the two signal lines produces a common mode signal that is canceled out by the difference amplifier at the destination.
In RS232 vs RS422 applications we have the differerence between a single ended system and a balanced line differential system. To see how ground path voltage can be a problem in RS232 applications see my web site and the page on NOISE and GROUNDING. www.beta-a2.com .
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A single ended input would use common as a reference for the signal.
For example: an amplifier input would be single ended if one signal wire, often times this is also the shield, is connected to the chassis of the amplifier, and this may be ultimately tied to physical ground or some other chassis. The other side of the signal is connected to the amplifier input. Note effectively we are amplifing the signal between common and the single input wire at the amplifier input. This is a difference measurement, but I do not really want to use that term here.
If at the source of the signal, a microphone for example, the common is connected to another common that thru some other path connects to the common of the amplifier, and suppose these are earth ground, then it is not unusual for there to be differences in voltage between different ground points. A voltage in this common path between the microphone and the amplifier adds to the desired signal and produces an unwanted addition to the signal. In this case probably 60 Hz hum. No solution here except to make sure the microphone common is floated, insulated from anything else.
A differential signal has neither signal line connected to common. In the case of the microphone the coil is connected between two wires neither of which is connected to common, and the shield is a separate wire. At the destination, amplifer input, the circuitry measures the difference between the two signal lines. If there is a noise signal in the common path, then if evenly coupled to the two signal lines produces a common mode signal that is canceled out by the difference amplifier at the destination.
In RS232 vs RS422 applications we have the differerence between a single ended system and a balanced line differential system. To see how ground path voltage can be a problem in RS232 applications see my web site and the page on NOISE and GROUNDING. www.beta-a2.com .
.
- Status