AboutDave Nyce Expertise I have been an electronics engineer for 25 years. I can answer questions on analog and digital circuits and my specialty is sensors.
Experience I am the inventor on 23 US patents, and also some foreign ones. Developed sensors for over 25 years. Licensed private pilot (airplane and rotorcraft), have HAM radio license. I'm not an expert in computer networking.
Expert: Dave Nyce Date: 12/23/2006 Subject: differential signal
Question Hi Dave Nyce,
I see in some documents people say that we can transmit differential signal.But I do not understand differential signal clearly. When people say differential signal, do they mention to voltage between two line (example we use RxD+ and RxD- to transmit 'receive' signal) ? If we transmit differential signal, do we need to transmit 'ground' signal? Example if I want to transmit 'Receive signal', I only use two line one for 'RxD+' and one for 'RxD-' ,there is not line for ground signal, at the receiver we can receive 'Receive signal' by using differential amplifier circuit, can't us? My standpoint is that we still receive 'Receive signal' accurately without ground signal from transmitter. But in electrical connector (use to transmit differential signal), there is ground pin, I don't understand why we need this pin, if we transmit differential signal by two line, we can receive signal without ground signal.
That is my standpoint but I am not sure that it's right.
Can you give me some ideals about this?
Thank you very much.
Thanh.
Answer A typical single ended signal could be with two wires, where one has a voltage of either 0V or 5V, and the other wire is 0V (ground). With a differential signal, there would be two wires, when one, for example, goes from 0V to 5V, the other goes from 5V to 0V (or other voltage levels are also popular). There is not really a need for a third 0V (ground) wire. But such a third wire is often included because it is used as a shield for the first two wires, sometimes improving noise immunity. If a shielded cable is used, the ground would connect to the shield. Also, the third wire can bring the transmit and receive circuits to the same ground level. This can also help to improve noise immunity.
