1. Diode PCB Parallel Termination
2. In certain cases, Schottky diodes or fast-switching silicon diodes can be used for transmission line termination, provided that the diode’s switching speed is at least four times faster than the signal rise time.
3. When the impedance of the breadboard and bottom board is difficult to determine, using diode termination can be a convenient and time-saving solution.
4. If ringing issues arise during system debugging, adding diodes can effectively eliminate them.
1. Typical diode termination. The low forward voltage drop (V_f) (typically 0.3 to 0.45V) of the Schottky diode clamps the input signal between GROUND-(V_f) and VCC+(V_f). This significantly reduces the overshoot (positive spike) and undershoot (negative spike) of the signal. In some applications, only one diode may be used.
2. The advantage of diode termination is that it replaces Thevenin or RC termination, which requires resistors and capacitors, and reduces overshoot and undershoot through diode clamping, eliminating the need for line impedance matching. Although the cost of the diode is higher than that of resistors, overall layout and routing overhead may be reduced, as precise impedance matching of the transmission line is no longer necessary. The disadvantage is that diode switching speed is generally limited, making it unsuitable for higher-speed systems.
3. PCB serial termination
4. PCB serial termination is achieved by inserting a resistor (R_S) (typically 10Ω to 75Ω) into the transmission line on the PCB as close to the source as possible. The purpose is to match the impedance of the signal source. The resistance of the inserted PCB serial resistor plus the output impedance of the drive source should be greater than or equal to the transmission line impedance (slightly over-damped). This strategy suppresses the signal reflected from the load by making the source end reflection coefficient zero (the load end is input with high impedance and does not absorb energy), and then reflects back from the source end to the load end.
5. The advantage of PCB serial termination is that each line requires only one termination resistor, needs no connection to the power supply, and has low power consumption. It can provide a current-limiting effect when driving a high capacitive load, which helps reduce ground bounce noise. The disadvantage is that when signal logic changes, due to the voltage drop across (R_S), a half-wave amplitude signal will appear at the source end. This half-wave signal propagates along the transmission line to the load end and is then reflected back to the source end, with a duration of 2(T_D) (where (T_D) is the transmission delay from the source end to the load end), meaning no other signal input ends can be added along the transmission line.
2. In certain cases, Schottky diodes or fast-switching silicon diodes can be used for transmission line termination, provided that the diode’s switching speed is at least four times faster than the signal rise time.
3. When the impedance of the breadboard and bottom board is difficult to determine, using diode termination can be a convenient and time-saving solution.
4. If ringing issues arise during system debugging, adding diodes can effectively eliminate them.
1. Typical diode termination. The low forward voltage drop (V_f) (typically 0.3 to 0.45V) of the Schottky diode clamps the input signal between GROUND-(V_f) and VCC+(V_f). This significantly reduces the overshoot (positive spike) and undershoot (negative spike) of the signal. In some applications, only one diode may be used.
2. The advantage of diode termination is that it replaces Thevenin or RC termination, which requires resistors and capacitors, and reduces overshoot and undershoot through diode clamping, eliminating the need for line impedance matching. Although the cost of the diode is higher than that of resistors, overall layout and routing overhead may be reduced, as precise impedance matching of the transmission line is no longer necessary. The disadvantage is that diode switching speed is generally limited, making it unsuitable for higher-speed systems.
3. PCB serial termination
4. PCB serial termination is achieved by inserting a resistor (R_S) (typically 10Ω to 75Ω) into the transmission line on the PCB as close to the source as possible. The purpose is to match the impedance of the signal source. The resistance of the inserted PCB serial resistor plus the output impedance of the drive source should be greater than or equal to the transmission line impedance (slightly over-damped). This strategy suppresses the signal reflected from the load by making the source end reflection coefficient zero (the load end is input with high impedance and does not absorb energy), and then reflects back from the source end to the load end.
5. The advantage of PCB serial termination is that each line requires only one termination resistor, needs no connection to the power supply, and has low power consumption. It can provide a current-limiting effect when driving a high capacitive load, which helps reduce ground bounce noise. The disadvantage is that when signal logic changes, due to the voltage drop across (R_S), a half-wave amplitude signal will appear at the source end. This half-wave signal propagates along the transmission line to the load end and is then reflected back to the source end, with a duration of 2(T_D) (where (T_D) is the transmission delay from the source end to the load end), meaning no other signal input ends can be added along the transmission line.
