application note TRU-600A code mark inversion (cmi) input data introduction the TRU-600A is a high performance, timing recovery module designed to extract a clock signal from an incoming digital data stream. the device provides an output clock signal along with a retimed and regenerated data stream. through the use of advanced saw filter technology the TRU-600A provides the timing recovery function with full and consistent compliance to sonet, sdh and ntt jitter requirements. the primary application of the TRU-600A device is the extraction of a clock signal from an incoming non-return to zero (nrz) data stream. this data type is often utilized in optical telecom transmission. an example is shown in figure 1(a). nrz data is a 1b1b code with one line bit for each associated binary bit. although initially designed for nrz timing recovery applications, it may be applied for other data formats. 1 0 1 1 1 0 0 1 0 1 0 1 (d) clock out (cmi data) (c) cmi data (b) clock out (nrz data) (a) nrz data binary digit cmi input data in addition to nrz data formats, the TRU-600A device is also commonly applied for clock extraction of input cmi data streams. cmi data is a 1b2b data format with two line bits for each associated binary bit. as illustrated in figure 1(c), a cmi low is represented by a positive transition in the center of the bit period. a cmi high is represented by no transition within the bit period, but with alternating polarity for each bit period. (a cmi low is transmitted as a 01, while a cmi high is either 11 or 00). because the TRU-600A was originally intended for nrz applications, it will interpret an incoming cmi data stream as a nrz stream at twice the binary rate. for this reason, when using the TRU-600A in cmi applications, the device should be tuned to twice the binary rate of the cmi data. for example, a TRU-600A @ 311.040 mb/s would be used to recover a clock signal from an input 155.52 mb/s cmi data stream. also note for cmi applications, that the resulting recovered clock will be twice the binary rate and may require division by 2 . vectron technologies, incorporated 267 lowell road hudson, nh 03051 tel: (603) 598-0070 fax: (603) 598-0075 e-mail: solutions@vtinh.com http://www.vectron-vti.com vectron technologies, inc. reserves the right to make changes to the product(s) and/or information contained herein without notice. no liability is assumed as a result of their use or application. no rights under any patent accompany the sale of any such product(s) or information. for additional information please contact:
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