Abstract: A method of approximating the bit error rate (BER) contribution to a data symbol stream of a first channel by additionally passing the stream through a second channel of controllable noise figure. The bit outputs of the two channels are sampled, compared, and a record is made of the number of times the sampled data (a one or zero) of the first channel differs from the data of the second channel. This number is a bounded multiple of the BER contribution of the first channel. A protocol independent parameter termed a transmission safety factor is defined to concisely and quantitatively represent symbol degradation. The method is applied in error detection in data transparent transmission systems, which can not benefit from techniques used in non-transparent systems such as parity violation, CRC, or code violation detection.

Abstract: A programmable delay line. The programmable delay line includes a series of delay cells which are programmably connected in series. The programmable delay line includes a main delay chain and auxiliary delay chains. The main delay chain includes unit delay cells. The auxiliary delay chains include a unit delay cell, and a delay cell which has a delay that is between one and two time greater than the delay through a unit delay cell. The delay resolution of the programmable delay line is less than the delay of a unit delay cell. The programmable delay line further includes a reference oscillator and calibration circuitry. The reference oscillator includes a series of unit delay cells, and generates a reference signal having a period which is an integer multiple of the delay of a unit delay cell. Variations in the delay of a unit delay cell influence the period of the reference signal.