LT1116 applicaTions inForMaTion High Speed Adaptive Trigger Circuit To achieve single supply operation, the input signal Line receivers often require an adaptive trigger to must be shifted into the pre-amplifier’s common mode compen sate for variations in signal amplitude and DC range. The input amplifier A1 adds a 1V level shift, while offsets. The circuit in Figure 3 triggers on 2mV to 200mV A2 provides a gain of 20 for high frequency signals. signals from 100Hz to 10MHz from a single 5V rail. The Capaci tors C1 and C2 insure that low frequency signals trigger level is the average of the input signal’s positive see unity gain. Bandwidth limiting in A1 and A2 does not and negative peaks stored on 0.005µF capacitors. Pairs of affect triggering because the adaptive trigger threshold NPN and PNP transistors are used instead of diodes to varies ratiometrically to maintain circuit output. temperature compensate the peak detector. 5pF 5V 3kΩ 1kΩ 1% 5V CABLE 1kΩ 5V VIN – 5V 4R A1 + 0.005µF 200Ω 500pF 200Ω LT1191 3MΩ A2 5V + + LT1192 – A3 0.005µF 3MΩ LT1006 – R 47µF 1000pF 100Ω 1kΩ 50Ω 3kΩ 1% 500Ω 5V C1 C2 0.1µF 100µF 0.1µF NPN = 2N3904 + Q PNP = 2N3906 LT1116 – Q TRIGGER OUT LT1116 • AI03 Figure 3. Fast Single Supply Adaptive Trigger 1116fc 8 For more information www.linear.com/LT1116