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How PCB Designers Should Consider Signal Levels And Operating Frequencies
Mar 19, 2018

For a circuit schematic, the PCB designer should first know the flow of its signal current. However, this problem is very simple. According to international practice, the input terminals are located on the left side of the circuit schematic, and the output terminals are located on the right side of the circuit schematic, at a glance.


The next thing to understand is the size of the signal current in the circuit and the operating frequency. When the magnitude of the signal current is represented by a gain, the understanding of the magnitude of the current can also be changed to the understanding of the level of the signal.


Under normal circumstances, the analog circuit output current is greater than the input current; in most cases, the digital circuit current is much greater than the analog circuit current. When the small-signal current circuit is adjacent to a large-signal current circuit, or the input and output ends of the same circuit are close together, the operation of the circuit is prone to unstable or self-oscillation. This phenomenon must be absolutely avoided. . For example, in a digital circuit, the magnitude of the signal voltage is on the same level as that of the power supply voltage, and the signal voltage of the high-frequency circuit on the receiving side in radios and televisions is only about 1/180 000 of it, so even if it is only 1 The /500 000 digital circuit signal is chained into the latter high frequency circuit, which will seriously hamper the reception and viewing of audio signals and television signals.


For example, when designing a circuit for a (analog) CD or DVD player on a PCB, there are both analog and digital circuits in the printed circuit board of the entire electrical device. Do not let the signal of the digital circuit interfere with the normal operation of the analog circuit. For this reason, such circuit schematics are often first divided into block diagrams with different functions for each part, and it is clearly identified which wires are signal lines, which wires are electric lines, and which lines are ground lines or shield lines.