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Clock Recovery Scheme for Ternary Duobinary AM/PSK Signal

IP.com Disclosure Number: IPCOM000060810D
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 86K

Publishing Venue

IBM

Related People

Hong, JH: AUTHOR

Abstract

The "eye" diagram of the envelope-detected baseband signal in the receiver is shown in Fig. 1. Also, as shown in Fig. 1, it is to be noted that the optimum threshold voltage for the timing detector for the symbols "1" and "0" is not the same as that for the non-data symbols. Therefore, if only one detector is used to extract the timing information from the "1" and "0" symbols, then the non-data symbols will cause a large timing error, such as Te in Fig. 1. In certain proposed standards, the non-data symbols are used during pseudo-silence (idle) to mark starting and ending frame delimiters, and to indicate forced data transitions made to break up long sequences of identical data symbols.

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Clock Recovery Scheme for Ternary Duobinary AM/PSK Signal

The "eye" diagram of the envelope-detected baseband signal in the receiver is shown in Fig. 1. Also, as shown in Fig. 1, it is to be noted that the optimum threshold voltage for the timing detector for the symbols "1" and "0" is not the same as that for the non-data symbols. Therefore, if only one detector is used to extract the timing information from the "1" and "0" symbols, then the non-data symbols will cause a large timing error, such as Te in Fig. 1. In certain proposed standards, the non-data symbols are used during pseudo-silence (idle) to mark starting and ending frame delimiters, and to indicate forced data transitions made to break up long sequences of identical data symbols. The only situation where the large timing error may degrade the system performance appreciably is caused by the non-data symbols following forced transitions because such a pattern can last for a long time. Fig. 2 shows a block diagram of a circuit which eliminates the large timing error associated with non-data symbols within a frame, that is, from the starting delimiter to the ending delimiter. The envelope detected ternary AM/PSK signal is first examined for the non- data symbols by the non-data detector 1. A phase-locked loop (PLL) 2 using charge pumps is used for clock recovery. This PLL has an additional control input 4 with which the charge pumps in the PLL can be disabled. To eliminate the large timing error associa...