A SFP with DDM function, what is DDM? Usually when we buy SFP transceivers, we will have options with its DDM functions, so what is DDM? Obviously a SFP with DDM is high-ender than one which without DDM functions. What the DDM use for?

DDM is Digital-diagnostic-monitoring which provides a user with critical information concerning the status of the transmitted and received signals. This approach allows for better fault isolation and error detection.

Optical module life prediction

DDM allows network managers to find potential link failures before system performance is affected. Failure notice, the system administrator can switch the business to a backup link or replace the suspicious device, so as to repair the system in the case of uninterrupted business.

Through real-time monitoring of the internal operating voltage and temperature of the transceiver module allows the system administrator to find some potential problems.

Vcc voltage is too high, will bring about the breakdown of CMOS devices; Vcc voltage is too low, the laser does not work properly.Received power is too high, damage to the receiving module.

Operating temperature is too high, will accelerate the aging of the device.

In addition, the monitoring of the received optical power, can monitor the performance of the lines and the remote transmitter.

Fault Locator

In optical link, locating the fault occurred fast loading of business is essential. ault isolation characteristics allows system administrators to quickly locate the position of a link failure.

This feature can locate the fault in module on the line; locally module or modules in the remote. Quickly locate the fault, reducing the time to repair the system.

Compatibility verification

Another function of DDM is to verify the modules compatibility. Compatibility verification is the analysis of the modules work environment to meet the data sheet or compatibility and related

standards. The performance of the module only in this compatibility work environment can be guaranteed. In some cases, due to environmental parameters beyond the data sheet or standard, will cause the module performance degradation, thereby result in the transmission error.

Environment like below is not compatible with the modules:

1. Voltage exceed the specified range

2. The received optical power is overload or lower than the receiver sensitivity.

3. Temperature is beyond the standard operating temperature range.

Conclusion：

Digital diagnostics monitor the SFP module’s temperature, receiver power, transmitter bias current, and transmitter power. Usually, the output of the physical value of each parameter is an analog voltage or current from the Trans impedance amplifier, the laser driver, or the post amplifier. Engineers use ADCs to digitize those physical values. With the digitized value, a microcontroller can then either process data as part of a control loop, trigger an alarm, or just record the data into a register.

if you want to know more about DDM, please refer to  What is DDM/DOM for Fiber Optic Transceiver?