Pulse shaping circuit using an analog delay line for fiber-optic systems

• Main Author: BROSNAN, MICHAEL JOHN
• Format: Patent
• Language: English; French; German
• Published: 25.03.1998
• Edition: 6
• Subjects: BASIC ELECTRONIC CIRCUITRY; ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; PULSE TECHNIQUE; RESONATORS; TRANSMISSION; TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHICCOMMUNICATION

A fiber-optic system includes a photodetector (16) for receiving optical signals from a light source (12), a threshold producing circuit (26) coupled to the photodetector (16), and a delay block (28) coupled to the photodetector (16). The threshold producing circuit produces a decision threshold voltage ((VT)) in response to signals from the photodetector (16). The delay block (28), formed of one or more stages of all-pass filter (60), delays the signals from the photodetector (16). The outputs of the delay block (28) and the threshold producing circuit (26) are connected to the inputs of a comparator (52). By providing a delayed signal, the decision threshold voltage ((VT)) is established in the comparator (52) before the delayed signals reach the comparator (52). In this manner, pulse width distortion is largely eliminated in the first bit of data in burst mode data and the dynamic range of the overall system is preserved. In some cases, a multi-staged delay (100) causes DC offset error in the delayed signal to the comparator (52). To reduce this error, a DC offset correction circuit (110) coupled to the delay block (100) corrects the DC offset error through the use of negative feedback across the delay block (100).