In/sub 0.53/Ga/sub 0.47/As junction field-effect transistors as tunable feedback resistors for integrated receiver preamplifiers

In/sub 0.53/Ga/sub 0.47/As active feedback junction field-effect transistors (JFETs) for use in integrated transimpedance photoreceivers are discussed. By varying the gate-to-source voltage V/sub GS/, the resistance can be continuously tuned between 3 and 40 k Omega with a drain-to-source capacitance of <10 fF. The temperature coefficient of resistance is between -5 and -20 Omega / degrees C (for V/sub GS/ less than the pinch-off voltage). The combination of large resistance and low capacitance can result in high receiver sensitivity without sacrificing amplifier dynamic range. The feedback FET was fabricated adjacent to 1.8- mu m-gate-length JFETs with transconductances of 110 mS/mm, gate-to-source capacitances of 1.3 pF/mm, and DC amplifier voltage gains of 100. The compatibility of these transistor structures indicates that an integrated preamplifier with dynamically tunable bandwidth can be realized.<
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