| 摘要 |
<p>The circuit (34) is of the type having an input section (12) and a shaping section (22). The input section includes a photodiode (14) and a transimpedance amplifier (16) with an AGC shunt device (19) connected between its input nodes (+,-). The shaping section includes, in order, an AGC amplifier (24), an equalizer amplifier (26), a buffer amplifier (42), and a filter (44). A controller (36) responsive to the photocurrent controls the impedance value of a dynamic impedance in the equalizer so that the frequency zero of the equalizer tracks the pole frequency of the input section as it changes in the course of changes in the value of its AGC shunt. This maintains the frequency response of the shaping section so that it continues to compensate for the frequency response characteristic of the input section. A trigger (52) responsive to the impedance value of the shunt activates the equalizer only when the shunt is active. Also disclosed is a particularly advantageous differential configuration for the equalizer which includes a diode bridge (76, 78, 80, 82) and four setting resistors (R1, R2, R1', R2') by which the break points for the frequency response can be set.</p> |
