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15.1 GENERAL DESCRIPTION . . . . . . . . . . . . . . 15-1

15.2 MODE OF OPERATION . . . . . . . . . . . . . . . 15-1

15.3 SPECIFICATION . . . . . . . . . . . . . . . . . 15-2

15.3.1 Electrical . . . . . . . . . . . . . . . . . . 15-2

15.3.2 Mechanical . . . . . . . . . . . . . . . . . . 15-2

15.4 DRAWING PACKAGE NUMBER . . . . . . . . . . . . . 15-3

15.5 RESPONSIBLE ENGINEER . . . . . . . . . . . . . . 15-3 CHAPTER 15 FIDUCIAL OUTPUT MODULE (FIDO)

15.1 GENERAL DESCRIPTION The FIDO is a module containing circuits that extract the fiducial pulse (T-zero) from the 476 MHz Main Drive Line and others that produce the fourth sub-harmonic at 119 MHz. The fiducial is signalled by means of a pulse added to the normal signal on the drive line, the result being a 476 MHz signal with one half cycle having an amplitude double the normal value. The output from a FIDO, consisting of a 119 MHz signal with a missing half-cycle to indicate T-zero, is fed to a number of Programmable Delay Units (PDUs), which use this information to provide the triggers for a sector of the Linac or appropriate sub-division of the other systems of the SLC.

15.2 MODE OF OPERATION The 476 MHz input from a directional coupler on the Main Drive Line is split by a power divider and matching network to provide the appropriate drive levels to the T-zero detector and the frequency divider. The T-zero detector is a sub-nanosecond tunnel-diode zero-crossing detector driven by a differential transistor pair, providing fast response time and excellent temperature stability. The load-line for the tunnel diode is biased such that the circuit is armed when the 476 MHz input reaches 1.5 V on the positive-going edge of the fiducial. The subsequent zero-crossing produces a very fast transition of the tunnel diode (< 200 ps). This triggers a delay-line mono-stable of about 8 ns duration which, in turn, resets the 119 MHz dividers. This blanks-out half a cycle of the 119 MHz and ensures that the correct phase exists when the counting resumes. A missing pulse detector in the PDU allows timing to be referenced to the next leading edge of the 119 MHz. A mono-stable with a time-constant of 2.5 ms inhibits operation of the detector by disturbances on the 476 MHz drive line between fiducials. Up to 10 independant outputs are provided, 4 for use with PDUs, 2 with PSUs and 4 for other triggering purposes. The output drivers are current sources and can drive 32 mA into 50 ohms, either single-ended or differentially. A provision for externally inhibiting the reset


FIDUCIAL OUTPUT MODULE (FIDO) Page 15-2 for the PSU outputs is provided. The output channels can be monitored at a socket which can be switched between them.

15.3 SPECIFICATION

15.3.1 Electrical o Input from Main Drive Line: Frequency 476 MHz Amplitude 2 V peak-to-peak RF +/- 2 dB 4 V peak minimum Fiducial Impedance 50 ohms o Output channels: Frequency 119 MHz with missing half-cycle fiducial Current 32 mA max. into 50 ohms o Reset Inhibit Input : Differential NIM - 16 mA each side - 50 ohms o Monitor point level : 1 V on 50 ohms o Resolution : Time-walk < 200 ps from +1 to +6 dB above threshold o Stability : Less than 40 ps change in timing for 10 degrees C. o Power : 117 V ac 10 W input: -2 V, -5 V & -12 V generated internally

15.3.2 Mechanical Standard rack-mounting unit, 3-1/2 in high. Front panel with following items: o 7 type "N" connectors: J0-J3 Output to PDU J4-J5 Output to PSU J11? Input from drive line


FIDUCIAL OUTPUT MODULE (FIDO) Page 15-3 o 5 BNC connectors: J6-J9 Trigger output J10 Monitor Point o LEMO 2-pin connector for reset inhibit. o Selector switch for monitor point.

15.4 DRAWING PACKAGE NUMBER 135-724

15.5 RESPONSIBLE ENGINEER E. L. Cisneros


 
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Contact (until Aug. 15, 1996): Jeffrey Miller
Owner: Bob Sass

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