S-51
The Tektronix Type S-51 is a synchronizing head for sampling oscilloscope systems such as the 3S2
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 connection. The input impedance is 50 Ω real in parallel with 1 pF. The minimum input sensitivity is 100 mVp-p and the maximum kickout is 400 mV. The maximum jitter of the generated trigger signal is specified to be 15 ps for input signals less than 5 GHz and 10 ps for input signals above 5 GHz.
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.
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, f_osc is a subharmonic of f_in.
- f_osc = f_in / n, where n is an integer between 5 and 90, inclusive
- f_osc is between 165 MHz and 285 MHz.
The approximate range of f_osc is adjustable.
Trigger pulses are produced at a 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 S-51 uses a BSM connector for its trigger output on the front panel. The trigger output signal is, of course, also available at the rear interface connector.
