PCB designers should first be aware of the direction of the signal current in a schematic circuit.But the problem is simple. According to international practice, the input end is located on the left side of the circuit schematic diagram, and the output end is located on the right side of the circuit schematic diagram.
Next, you need to understand the size of the signal current in the circuit and what the operating frequency is.In the case that the size of the signal current is expressed by gain, it is also possible to change the understanding of the current size to that of the signal level.
Generally, the output current of the analog circuit is greater than that of the input circuit.In most cases, the current of the digital circuit is much greater than that of the analog circuit.When a small signal current circuit is adjacent to a large signal current circuit, or when the input and output ends of the same circuit are close together, the operation of the circuit is prone to unstable state or self-excited oscillations, which must be absolutely avoided.In digital circuits, for example, the size of the signal voltage and the size of the power supply voltage on the same level, high frequency circuit in radio and TV receiver signal voltage is only about 1/180 of its 000, so even if only 1/500 000 digital circuit signal after a series of high frequency circuit, can seriously interfere with the sound signal and TV signal of xin and viewers.
For example, when designing a circuit of a (analog) CD or DVD player in a PCB, both analog and digital circuits in the printed circuit board of the entire electrical installation, special care should be taken not to allow the signal of the digital circuit to interfere with the normal operation of the analog circuit.For this reason, the circuit schematic diagram of this kind of circuit is usually first divided into block diagram of each part with different functions, and it is obvious that which wires are the signal line, which wires are the electrical pile line, and which wires are the grounding line or shield line.