A versatile, portable triggered differential USB pulse generator

Pulse heads

Internal construction of pulse head

The PicoSource PG900 Series are low-jitter triggered differential USB pulse generators. Pulse outputs are optimized for broad spectral content (fastest transition time) to best suit spectral and time-domain transmission and reflectometry measurements. An internal clock is provided for stand-alone, self-triggered operation and trigger input and output allow the generators to source or respond to system triggers. Differential outputs ensure that the proliferation of gigabit differential interconnect and systems can all be addressed (e.g. SATA, USB3, HDMI, Ethernet).

Essential to any differential test or measurement is the ability to adjust for small but significant velocity and path length differences that are bound to exist in any measurement setup. The PG900 pulse outputs can each be adjusted (time-skewed) in 1 ps increments to deskew path differences before the measurement, or to deliberately stress a transmission path with timing skew.

Despite their small size and portability the PicoSource PG900 generators pack quite a punch, with integrated Step Recovery Diode outputs of up to 6 V pk each into 50 Ω. That’s a whopping 12 V pk differential pulse amplitude to drive lossy paths or stress system ports. Outputs are adjustable in 10 mV steps down to 2.5 V pk. A user-settable amplitude limit is provided to protect more sensitive system ports and 20 dB attenuators are supplied fitted to the pulse outputs for small-signal and optimum-match applications.

Step Recovery variable amplitude pulse

The positive (fast rise) and negative (fast fall) pulses are both ground referenced and each pulses in opposite polarity to their user selected amplitude. This amplitude (the 'mark') is held for the user-selected pulse width and then returns to ground. Further pulses are prevented for the user set hold-off period and thereafter will repeat at 40 ns after the next received trigger. When the internal clock is selected, the pulse will repeat at the user-set period and holdoff is inactive. An output trigger is generated 40 ns before every pulse, however initiated.

Pulse transition time is typically 55 ps and spectral content (compared with a simulated ideal infinitely fast edge) extends to around 13 GHz @ –10 dB.

The negative (fast fall) pulse can be selected for even faster transition time by selecting 'fast' rather than 'smooth' mode. Pulse aberration is compromised but transition time is typically 45 ps and spectral content extends to around 14 GHz @ –10 dB.

Typical pulse shape as captured on a PicoScope 9300 20 GHz Sampling Oscilloscope are shown to the right.

Tunnel Diode Head fixed-amplitude pulse

The positive (fast rise) and negative (fast fall) pulses are both ground-referenced and each pulses in opposite polarity to its user-selected amplitude. This amplitude (the 'mark') is held for the user-selected pulse width and then returns to ground. Further pulses are prevented for the user-set holdoff period and thereafter will repeat at 40 ns after the next received trigger. When the internal clock is selected, the pulse will repeat at the user-set period and holdoff is inactive. An output trigger is generated 40 ns prior to every pulse, however initiated.

Pulse transition time is typically 55 ps and spectral content (compared with a simulated ideal infinitely fast edge) extends to around 13 GHz @ –10 dB.

The negative (fast fall) pulse can be selected for even faster transition time by selecting 'fast' rather than 'smooth' mode. Pulse aberration is compromised but transition time is typically 45 ps and spectral content extends to around 14 GHz @ –10 dB.

Typical pulse shape as captured on a PicoScope 9300 20 GHz Sampling Oscilloscope is shown to the right.