| 摘要 |
A continuously tunable wideband optical communications receiver exhibits optimum performance across multiple octaves of received signal bandwidth. The receiver's transimpedance preamplifier input stage includes a variable transconductance field effect transistor, whose transconductance exhibits a very steep non-linear variation with drain current over the operational bandwidth of the transimpedance amplifier. As a result, the bandwidth of the transimpedance amplifier and therefore the receiver can be tuned to accommodate the detected data rate. The data rate of the received signal (known either a priori, or extracted by a clock recovery circuit) is used to adjust drain current and thereby tune the operational bandwidth of the receiver. A bandwidth control code look-up table previously stored in memory during a calibration phase of operation is employed by the receiver's microcontroller to generate a digital code representative of an control voltage to be output by a digitally programmable current control circuit. This control voltage is applied to a control port of the transimpedance amplifier so as to set the drain current supplied to the HJFET which, in turn, sets its transconductance, and thereby the effective operational bandwidth of the receiver.
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