S-51
The Tektronix S-51 is a synchronizing head for sampling oscilloscope systems such as the 3S2 or 7S12 which use S-series sampling heads.
From a periodic input signal in the 1 GHz to 18 GHz range, the S-51 generates trigger pulses which have a fixed time relationship with the input signal. The input is a 50 Ω SMA connector. The trigger output signal is available through a BSM connector on the front panel as well as through the internal interface.
Equivalent-time sampling equipment generally requires the input signal to be repetitive. The S-51 is more restrictive; it is specifically designed for periodic signals. This is true of all oscilloscopes that use synchronization instead of triggering.
Key Specifications
| Input impedance | 50 Ω real // 1 pF |
|---|---|
| Input sensitivity | min. 100 mVp-p |
| Kick-out | ma. 400 mV |
| Jitter | max. 15 ps for input signals < 5 GHz, max. 10 ps above 5 GHz |
Internals
The S-51 contains a tunnel diode sync oscillator that oscillates at about 200 MHz (165 MHz to 285 MHz). The input signal is coupled with this oscillator, resulting in injection locking. When locked, fosc is a subharmonic of fin:
- fosc = fin / n, where n is an integer between 5 and 90, inclusive
- fosc is between 165 MHz and 285 MHz.
The approximate range of fosc is adjustable.
Trigger pulses are produced at the beginning of a cycle of the sync oscillator. After each trigger pulse is produced, the sync oscillator is turned off for about 15 microseconds. As a result, the S-51 produces trigger pulses at a repetition rate of approximately 67 kHz. Even without any input, the S-51 will produce trigger pulses at approximately 67 kHz.
The tunnel diode, D2 in the schematic, that forms the sync oscillator is Tek part number 153-0041-00.
