Secondary Side-Channel Wireline Communication Using Transmitter Clock Frequency Modulation

A secondary communication link, or side-channel, is proposed, which uses binary frequency shift keying to modulate the frequency of a high-speed wireline transmitter clock. This side-channel data is then received using the corresponding receiver’s conventional clock and data recovery (CDR) circuit. An analysis of the CDR loop parameters demonstrates that, within certain limits, the side-channel does not impact the signal integrity of the primary high-speed data. Measurements were made on a side-channel prototype using a 56-Gb/s PAM-4 (half-rate 14-GHz clock) transceiver in 7-nm FinFET technology through a 15-dB loss channel. Over 104 side-channel bits were transmitted at 50 kb/s, and the side-channel remained error-free with no visible impact on the high-speed link.