LMH0074: Criteria for carrier detection

Hi Kawai-San,

Based on insertion loss of the cable and maximum cable length that device can equalize, we can determine minimum carrier level. For example, LMH0324 can equalize 600m at SD data rate. Looking up B1694A cable insertion loss at 135MHz, we see 2.24dB per 100ft or per 33.33m. Therefor (600/33.33)*2.24 ~ 40dB. Since minimum launch amplitude is 700mV, this means we should be able to detect energy as low as 7mV peak to peak.

Another parameter that is important for detecting carrier is the length of the pathological pattern. For example, at SD pathological pattern could be as long as 60uS. Therefore carrier detect should not declare loss of carrier if there is very low frequency content for this period of time.

In summary, by realizing maximum cable reach and minimum launch amplitude, we can estimate approximate input level to trigger carrier detector.

Regards,,nasser