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, 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 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.

Pictures

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