The DC-DC converter supplies power to the various circuits in the overall system. Although each circuit may perform well on the test bench, the overall performance of the system often fails to achieve the performance of each circuit. why? There are many potential factors, and the overall grounding system for each circuit in the system is the primary cause. Designers need to be very clear about how each circuit is grounded and whether there is a ground loop in the system.
A ground loop is formed when there is more than one ground connection between two circuits and/or systems. Repeating the ground path is equivalent to forming a loop antenna that receives the interface signal (the current is converted to a voltage by the grounding resistor). The consequence of receiving the ground loop induced voltage is that the system's ground-to-ground reference voltage is unstable with the superposition of induced voltages. These induced noise voltages are part of the overall system response!
In addition, the ground loop forms a common line, causing the ground current to return to the ground-to-ground origin of the system via more than one channel. For example, the power of multiple computers is connected to each other through the ground in a common office wiring configuration, but can also be connected through data communication wiring. Therefore, computers are often connected to each other by more than one grounding channel. When there are multiple grounding channels between multiple computers, the resulting configuration is called a "ground loop." Whenever a ground loop occurs, the ground reference point receives the superimposed signal, creating system interference and noise.
A measurement, communication, or video system creates a ground loop when certain components in the system are powered by different grounds, rather than other components in the system, or when the ground potential is different between the two circuits in the system. Usually, the potential difference to the ground connection causes current to flow. This modulates the circuit input and other signals appear in the normal input. In the example shown in Figure 1, two grounded instruments are grounded through signal lines and main ground lines are interconnected. In this case, a 1A current in the line creates a voltage difference of 0.1V between the two instrument ground points.
Figure 1 Typical ground loop
Due to the voltage difference between the instruments, the signal in the interconnecting conductor will add this voltage difference to the signal, causing the voltage to appear "communication". This is one reason why 60 Hz noise is heard in the audio signal (or horizontal interference in the video signal). Another problem is the current flowing in the ground of the signal cable. This current is also transmitted to cables and equipment. Designers always pay attention to the grounding of the ground, but often do not optimize the design, thus eliminating the sensitivity of the noise floor. Therefore, when designing the internal grounding line of the system correctly, it is the most basic requirement to ensure that the ground loop current does not cause system problems.
As another example, a ground loop is a common problem when multiple audio-visual system components are connected together. Common noise in audio systems is often caused by ground loop problems. In addition, audible "communication" is also a typical ground loop problem (depending, of course, on the AC supply voltage frequency used in the country). Of course, the most common example of a ground loop problem is when the system uses an instrument connected to the outlet and the other instrument connects to a different grounded outlet in the room.
Ideally, each system in a room should be connected to the same ground, and the signal/antenna network would eventually be connected to the same ground point. This is ideal because the grounding of the system and each instrument is point-to-point connected by the same ground reference (central ground star connection mode). In this case, it must be considered that some devices (and systems) also use shielded wire links. Current flows from one device to another through the ground and then returns to the first device through the shielded cable. This loop also picks up interference from nearby magnetic fields and RF transmitters such as cell phones. As a result, an unwanted signal that is amplified is heard. By the way, the ground loop does not cause problems under the following conditions:
1) The wires in the loop do not carry current;
2) The loop is not exposed to an externally changing magnetic field;
3) There is no radio frequency interference nearby.
If there is current flowing in the ground, noise interference will occur when there is a certain potential difference. In addition, a small voltage difference adds noise to the signal. This situation can cause audio hum, video interference images, and computer network transmission errors.
Good analog system design, analog system test and measurement need to carefully design the system grounding channel to avoid ground loop.
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