The present invention relates to the processing of a signal in order to determine jitter properties of the signal.
Jitter is a major cause for bit errors in digital communication systems. Jitter describes timing aberrations of a signal from a predefined signal course, e.g. delays of a signal caused by a lossy transmission channel. Bit errors occur if a receiver of a digital communication system detects a logical zero in a received bit stream instead of a logical one or vice versa. A measure for bit errors in digital communication systems is the bit error ratio—BER.
Particularly, the BER depends on the quality of a received signal containing digital data. Receivers of digital communication systems are adapted to sample the received signal with a predetermined sampling rate. However, jitter of the received signal may cause a bad sampling of the digital data transmitted with the received signal causing bit errors.
The theoretical model of total jitter—TJ—distinguishes between random jitter—RJ—and deterministic jitter—DJ. RJ is caused by thermal and noise effects. Thus, it is unbounded and may be described by a Gaussian probability density function. In contrast to RJ, DJ is bounded, i.e., it has definite amplitude limits and is by nature a peak-to-peak value. DJ is further distinguished in periodic jitter—PJ—, bounded uncorrelated jitter—BUJ—, and data dependent jitter—DDJ.
DDJ is a function of bit patterns and further distinguished in Duty Cycle Distortion—DCD—and Inter-Symbol Interference—ISI. ISI is usually caused by long and short bit cycles and results from bandwidth limitations or from loss within transmission lines while DCD is caused by voltage offsets between differential inputs and differences between transition times in a system.
Until now Jitter decomposition is known using a Real Time or Sampling Scope, as described in the publication “Jitter Analysis: The dual-Dirac Model, RJ/DJ, and Q-Scale”-White Paper, 21 Jun. 2005.
State of the Art for Bit Error Ratio Testers—BERT—is separating RJ and DJ using a BERT scan methodology. Such BERT might also be used to measure TJ, using a so-called Optimized BERT Scan Method.