| 摘要 |
A circuit for receiving light incorporates an amplifier (12) having a differential output and is so designed that the positive-phase and antiphase output (Vp, - Vp) from the amplifier (12) are inputted to a comparator (34) always at optimum threshold levels respectively. For this purpose, the peak voltage (Vi) of the positive-phase and antiphase outputs from the amplifier (12) is sensed by a peak value sensor (26) and the peak voltage (Vi) is converted into a current by a voltage-to-current converter (28) having a transconductance (gm). The converter (28) has a differential output and outputs a positive-phase output (I+ = gm Vi) and an antiphase output (I- = gm Vi) respectively. These currents (I+, I-) are converted into voltages by resistors (R10, R12) and the resultant voltages are substracted from the positive-phase and antiphase output (Vp, - Vp). Thereby, the outputs (Vp, - Vp) are mutually level-shifted by the same voltage value respectively. The signals thus level-shifted are inputted to the positive-phase and antiphase inputs of the comparator (34) respectively. <IMAGE> |
