How to solve the problem of the online splitter of the PCB circuit board?
Any long signal path on the printed circuit board of an online splitter can be regarded as a transmission line. If the line propagation delay time is a much shorter rise time signal, then the rise of the signal generation reflects that the Lord must be submerged. No longer will overshoot, kickback and ringing, most existing MOS circuits, because the rise time line propagation delay time ratio is greater, so the alignment can be grown in meters without signal distortion. Faster logic circuits, especially high-speed emitter-coupled logic.
Because of the fast speed of the integrated circuit of the online splitter, there are no other measures to the edge, and the trace length must be shortened in order to maintain signal integrity.
There are two methods for the online splitter to make the high-speed circuit work on a relatively long line without serious waveform distortion, TTL falling edge fast Schottky diode clamp method, so that the excess is clamped by more than one diode below the ground potential level , Thereby reducing the amplitude of the backlash, slowing the attenuation of the rising edge over-allowed, but the relatively high output impedance of the circuit in the H level state. In addition, because the level H country exemption is large, so the problem of recoil HCT series equipment is not very prominent, the effect of using a Schottky diode clamp and series resistor termination method combined with the improvement will be more obvious.
When a fan’s signal line, the online sub-board machine is at a higher bit rate and speed advantage rate, the method described above is often not enough for TTL shaping. Because there is a reflected wave line, they tend to be synthesized at a high rate, resulting in severe signal distortion and reduced interference. Therefore, in order to solve the reflection problem of the online splitter, another method is commonly used in the emitter-coupled logic system: the line impedance matching method. In this way, the control can reflect and the signal integrity is guaranteed.
Strictly speaking, the online splitter has a slower speed, and the traditional TTL edge and CMOS devices, the transmission line is not very necessary. There is a faster edge speed for high-speed emitter-coupled logic devices, and transmission lines are not always required. However, when using transmission lines, they must predict the advantages and oscillations reflected by the connection delay and control impedance.