THANKS TO RECENT ADVANCES, many test instruments are able to perform a variety of tasks. For example, Picosecond Pulse Labs' model 4022 is labeled as a time-domain-reflectometer/ time-domain-transmission (TDT) enhancement module. Yet it does not need to be used for these applications. In fact, this pulse generator can supply less than 10 ps risetime differential test signals for the testing of numerous ultra-highspeed logic families. The capabilities of the model 4022 are examined in an application note from the company titled, "Generation of 10 ps Risetime, Differential Test Signals."
According to the three-page document, the model 4022 was originally designed as a risetime enhancer for use with Agilent and Tektronix time-domain reflectometers (TDRs). Yet this generator does not need to be triggered by a dedicated TDR pulse. It can be triggered by almost any other pulse generator.
To achieve ultimate low-jitter performance, the company recommends that the measurement oscilloscope not be triggered by the trigger output from the pulse generator that is used to trigger the 4022. Any jitter present between that generator's trigger and the main pulse outputs would immediately translate into added jitter on the 4022's pulses. To achieve the lowest jitter triggering, use a pick-off tee for the oscilloscope's trigger. Next, insert a fixed length of high-quality coaxial cable between the pickoff tee and the 6-dB tee. The note ends by showing how an ultra-narrow impulse generator can be configured simply by adding an impulse forming network (IFS) between the pulse head and attenuator.
Picosecond Pulse Labs, 2500 55th St., Boulder, CO 80301; (303) 443-1249, FAX: (303) 447-2236, Internet: www.picosecond.com.