串入电容是为了高速信号阻抗匹配吗？CDCLVC1102PW/AMC1306/tms320f28377d

感谢您的回复。时钟信号是20MHz，您提到的“频率不太高的应用”，是指多少MHz呢？串入上AC耦合电容，相对于不串入有什么好处呢？因为不加，这个串行信号读取也是没有问题的，因为TI得很多案例，都是没有串入这个AC电容的，我们正在调试正常运行的电路也没有串入这个AC电容。

还有一个问题，就是cdclvc1102可以驱动多少个芯片？是cdclvc1102最大输出电流能力确定的吗？AMC1306 datasheet上clk输入管脚耗电量不明确，cdclvc1102最大输出电流50mA，但没有关于输出电流与输出电压幅值的关系图。

耦合分为交流耦合和直流耦合

原理图上是交流耦合

你用的是直流耦合

各有各的优缺点

Hello ,

looks like this a modified schematic from the Altium design files. Please see the variants information in Altium, which show that some resistors are DNP.

(1) I had the 0.1uF capacitor on the data signal, it does not have an effect in the impedance matching of the data signal. The 0.1uF capacitor would be low impedance to the 20Mhz data signal. This was kept for testing. Please remove this capacitor and replace with a short. Thanks, I will add a note in design guide to make it clear. 

(2) Some resistors are for debugging.

R12 and R16 on clock lines are DNP when using the Manchester encoded version of AMC1306 as there is no need to give the clock back to C2000 when data is Manchester encoded.

R4, R7, R15 and R17 are used for debugging either open or short according to the need. This can be eliminated.

R5, R13, R3,R6 are for impedance matching (series termination). 

Also,  R1 and  R8, or  R11 and R14 are placed for parallel termination, this should not be placed when using series termination. After testing i have seen that series termination works best.

(3) I had long distance and also a cable between AMC1306 and C2000 about 10cm. The issues due to propagation delay is eliminated by using Manchester encoded data. However impedance matching is required for signal integrity. Example: one of the problems I have seen with out impedance matching is excessive ringing at the signal edges. I have done only a rough impedance matching using the resistors, but I have not done the impedance control in the PCB manufacturing. At 20Mhz one may not see a problem depending on the board and cable, I would still put it as provision.

also note, CDCLVC1102 has a internal series termination resistance for 50Ohm. You may need to add to this.

(4) TIDA-00915-C does have provision for 4 clock input to the C2000, but since I am using the Manchester version of the AMC1306, I have DNP resistors on these clock lines. effectively I have only 4 AMC1306, being driven. This works very well for TIDA-00915, unfortunately, I do not have any info on the max number of AMC1306. Please do post on the Clock and Timing Forum about max number of loads for CDCLVC1102.

Regards

Nelson

现在就剩下最后一个问题了，如何评估CDCLVC1102的驱动能力。