Terminator resisntors + IC553 driver clock

[flote21]

Hello,

I have a question about the 33ohm terminator resistors. According to the datasheet of this clock driver:

"A minimum number of external components are required for proper operation. A decoupling capacitor of 0.01 µF should be connected between VDD on pin 1 and GND on pin 4, as close to the device as possible. A 33 Ω series terminating resistor may be used on each clock output if the trace is longer than 1 inch.

To achieve the low output skew that the ICS553 is capable of, careful attention must be paid to board layout. Essentially, all four outputs must have identical terminations, identical loads and identical trace geometries. If they do not, the output skew will be degraded. For example, using a 30Ω series termination on one output (with 33Ω on the others) will cause at least 15 ps of skew."

I am using this driver for clocking 4 ADCs. Then I don't know where I have to place the 33ohm resistors, close to the clk pin of the ADC or close to the output pins of the clock driver?

On the other hand if I route the tracks to the 4 ADCS with the same lenght, Should be neccessary to put also the 33ohm resistors?

Thanks.

 

[flote21]

I put a network resistor in front of the ICS553 and I have interferences...So maybe I have to use the terminator resistors close to the ADCs....Any suggestion?

Hello,

I have a question about the 33ohm terminator resistors. According to the datasheet of this clock driver:

"A minimum number of external components are required for proper operation. A decoupling capacitor of 0.01 µF should be connected between VDD on pin 1 and GND on pin 4, as close to the device as possible. A 33 Ω series terminating resistor may be used on each clock output if the trace is longer than 1 inch.

To achieve the low output skew that the ICS553 is capable of, careful attention must be paid to board layout. Essentially, all four outputs must have identical terminations, identical loads and identical trace geometries. If they do not, the output skew will be degraded. For example, using a 30Ω series termination on one output (with 33Ω on the others) will cause at least 15 ps of skew."

I am using this driver for clocking 4 ADCs. Then I don't know where I have to place the 33ohm resistors, close to the clk pin of the ADC or close to the output pins of the clock driver?

On the other hand if I route the tracks to the 4 ADCS with the same lenght, Should be neccessary to put also the 33ohm resistors?

Thanks.

 

[dick_freebird]

The resistors are an attempt to impedance-match the
board traces (inclusive of the driven load) so that you
do not have gross ringing or staircasing (over- or under-
terminated) and the description implies a source-
terminated scheme. If you're worrying about pS of
jitter, a half-scale overshoot/undershoot couple or a
plateau at VDD/2 (with your far end input threshold lying
variably and unpredictably on either side of it) at trace
time-of-flight will absolutely ruin your day.

 

[flote21]

Thank you for your answer. But finally the problem was the netwark resistor. The pads of the footprints were very close and interferences were produced between the signals. After isolating the network resistor and add terminator resistors close to the ADC, the interferences were gone..

 

[ssundar.shan]

Hi flote21,
The series Termination resistors are used for Impedance matching. Hence the series resistors has to be placed at the source end (Near to clk IC).
In your case, you need to route the 4 traces of equal length (Length Matching) to avoid any data loses or interferences.

Please let me know if you need any other details.

Thanks and Regards,
Shunmuga Sundaram