Current Project: Most systems that process High-Definition analog signals would benefit by using differential, or balanced, interface signals. Many transmission line effects can be neutralized especially long distance. For some audio dudes I've known long distance can be defined as from one side of the shelf to the other. A whopping foot and a half. Ha ha!
Differential Circuits Provide Various Advantages...
There are two classes of differential circuits. Balanced and Unbalanced. While considering the benefits it can be assumed that the effects are universal for both types.
The explanation requires understanding some of the properties of differential receivers and good grounding.
Power Supply Rejection: This is the sensitivity of a device to the noise on it's power supply contacts and how much will couple to the output signal. It is measured in decibels. It is usually a low value by audio standards. Fortunately... The noise on power supplies 'should' be very low so when the rejection factor is observed it will be acceptably below signal levels. This is a simple example of why power supply layout and decoupling is so important.
Common Mode Rejection: This is the sensitivity of a device to signal or noise that is common on both inputs (in phase). Common signals are rejected, naturally, by the differential input of the device. Normally... Differential signals are transmitted in the form of two signals that are 180 degrees out of phase. This is considered a balanced signal. Any coupling between the signals, including noise, is usually common on both. Rejecting the common (erroneous) signals increases the quality (fidelity) of the signal the device 'differentiates' while receiving. It may not be obvious here why it is still useful transmitting single-ended where one signal is just ground. Remember... This method is used for rejecting impedance and coupling effects for transmission lines which single-ended configurations will suffer from the same effects.
Transmission Line Shielding Should Not Be Considered A Ground:
When a current flows through a shield it creates an energy field capable of coupling to the conductors it is shielding. Somewhat defeating it's purpose. A better interface practice is to include an additional conductor within the shielded bungle that forms the ground reference between circuits (systems). The shield in this case should be connected at the signal 'source' end and left floating (unconnected) at the 'destination' end. This practice was known as 'telescoping' the shield.
Conclusion...
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