What is PAM4 Clock Recovery?
One method to retime PAM4 data on the receiver side of a link is to use a clock recovery approach. In most cases, this involves some sort of clock and data recovery (CDR) functionality. Clock is initially recovered from the input data signal and is then used to retime that same data signal.
What does PAM4 Clock Recovery do?
In a typical setup, some sort of phase/frequency detector is utilized to determine the phase relationship between the incoming data signal and the receiver side generated clock. Any error in the phase / frequency between the two signals is then fedback to the local voltage controlled oscillator (VCO) that makes the correct adjustments. Some CDR architectures need a local low frequency clock to move the VCO close to the proper frequency range while others don’t. Once the CDR is “locked” to the data, the input data is retimed to the local clock source and thus can be processed error free by the rest of the downstream circuitry. Clock recovery on the receiver side is one of the most important functions on the receiver side.
What are some applications of PAM4 Clock Recovery?
PAM4 clock recovery or clock and data recovery units can be found mostly in test equipment and telecommunication products that utilize that type of signaling. PAM4 has become popular in the telecom world recently since initial drafts of the 400GE standard include this type of signaling on both sides of the Tx and Rx sections. For example, the Tx has 8 inputs running at 25Gbaud/s PAM4 and 4 outputs running at 50Gbaud/s. In reverse fashion, the Rx has 4 inputs running at 50Gbaud/s and 8 outputs running at 25Gbaud/s. The Tx needs PAM4 clock recovery on its input PAM4 signals. For the Rx, the most popular approach currently is to use DSP although future implementations could still utilize a CDR solution. Since laboratory equipment is needed to test these 400GE products, they will need PAM4 clock recovery as well.
A few examples of ADSANTEC PAM4 Clock Recovery:
ADSANTEC offers several PAM4 clock recover solutions for test equipment manufactures. These include the ASNT2110-KMF, the ASNT2112-KMF, and the ASNT8160-KMF. All three offers are similar expect that they cover different frequency ranges. The full rate ASNT2110-KMF covers the frequency range from 25.5GHz to 32.5GHz. The full rate ASNT2112-KMF covers 21GHz to 26GHz. The half rate ASNT8160-KMF covers the same range as the ASNT2110-KMF, but can process input data signals at twice the input data rate. All three solutions are currently used in various test equipment manufactures’ solutions.