Multiple-threshold optical receiver for a variable-rate digital data transmission system

An optical receiver for equipping a variable-rate digital data transmission system of the optical type in which information is transmitted in the form of light pulses coded in accordance with a code having a constant direct-current component, said optical receiver being constituted by a photodetector stage in series with a transimpedance circuit whose output is applied via a capacitor of a processing circuit to a first set of two threshold comparators having symmetrical threshold values, the outputs of said comparators being applied to a transcoding circuit, said processing circuit comprising said capacitor to eliminate the direct-current component and a threshold-generating circuit receiving the output signal of the capacitor and for generating said symmetrical threshold values which are variable as a function of said output signal level, said values being selected in said threshold-generating circuit from a plurality of distinct discrete values which are predetermined so as to cover a large dynamic utilization range, said threshold-generating circuit including at least a second set of two threshold comparators to compare said output signal to symmetrical constant threshold values, and a decision logic circuit controlled by said second set of comparators to select the said variable threshold values.