CompuScope 82GC 101CompuScope 82GC External ClockExternal clocking is a very powerful feature in a digitizer. It allows the user to synchronize the digitizer to anexternal system.On the CompuScope 82GC, external clock signal must be a continuous sine wave signal of amplitude between225 mV RMS and 500 mV RMS. Note that the external clock input is AC coupled, so DC biases get canceled.The allowable external clock frequency is between 1 GHz and 10 MHz. An SMA connector is employed for theExternal Clock input because of its superior high frequency response at 1 GHz ñ BNC connectors start runninginto bandwidth limitations at such high frequencies.PLEASE NOTE:THE EXTERNAL CLOCK ILLUSTRATIONS IN THIS SECTION DEPICT THE CLOCK SIGNALAS A SQUARE WAVE FOR CLARITY, PLEASE FOLLOW THE RECOMMENDATIONS ABOVETO ACHIEVE PROPER OPERATION.In single channel mode, sampling is done on both the ìrisingî and ìfallingî edge of the sine wave.Figure 63: External Clocking in single channel modeIn dual channel mode, sampling is done on only the ìrisingî edge of the sine wave.Figure 64: External Clocking in dual channel modeNote that high-speed waveform digitizers are very sensitive to phase noise and duty cycle of the external clockinput. All efforts should be made to minimize jitter and distortion on the external clock signal.Care should be taken not to inject a TTL or CMOS signal (0 to 5 Volts) into the external clock input, as it mayresult in saturation of the input circuitry.
