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LOCAL OSCILLATOR PROGRAMMING
Introduction
The beam spectrum selected harmonic –called the “operating frequency”– is mixed with the Local
Oscillator (LO) frequency to obtained the Intermediate Frequency (IF).
Mixing two signals produces many frequencies, one of which is of interest to us: |ƒ
op
– ƒ
LO
|.
The BPM module uses 21.4 MHz as intermediate frequency. As a consequence, the LO frequency
can have either of two values:
ƒ
LO
= ƒ
op
– 21.4 MHz, or ƒ
LO
= ƒ
op
+ 21.4 MHz
The IF filters have a typical 3-dB bandwidth in excess of 500 kHz. However, BPMs made for
very large machines may have narrower filters to reject their revolution frequency.
The phase-locked synchronous demodulator tracks the carrier signal over a wide range:
21.25 MHz
≤
ƒ
IF
≤
21.55 MHz
The on-board local oscillator frequency synthesizer uses an MB87003A circuit from Fujitsu. It
requires a 17-bit serial word for its programming
1
. The BPM module implementation of this circuit
is described in an annex to this manual
2
.
Changing the LO frequency
Note: It may be necessary to change the LO frequency if the difference between your beam chosen
harmonic and the BPM operating frequency exceeds 100 kHz.
The 17-bit word is generated by a small daughter board plugged on the BPM module main board.
Each bit is programmed high or low by a solder bridge to 5V or ground:
• Solder bridges on the F-Key components side are pull-ups.
• Solder bridges on the F-Key solder side are pull-downs.
Programming bits are numbered as follows:
bit-17 & -16
bit-14
bit-13
bit-12
bit-11
bit-10
bit-9
bit-8
bit-7
bit-6
bit-5
bit-4
bit-3
bit-2
bit-1
bit-0
Components side
F-Key
Note: The synthesizer receives effectively 17 bits from the F-key. The first programmed F-key bit
is sent twice, as bit17 and as bit16.
1
Fujitsu Telecommunications Products, 1992 data book, Cmos PLL frequency synthesizer, page 2-3 thru 2-14
2
New Generation Electronics Applied to Beam Position Monitors, K.B. Unser, page 4, Tbp.: proceedings of the 1996
Beam Instrumentation Workshop, Argonne.
BERGOZ Instrumentation
Multiplexed
01630 Saint Genis Pouilly, France
Beam Position Monitor
Tel. +33-450.426.642
Fax +33-450.426.643
Page 20
User’s manual
BERGOZ Instrumentation - 01630 Saint Genis Pouilly, France - Tel.: +33-450.426.642 - Fax: +33-450.426.643
TVA-VAT-IVA-USt. Nº FR88414997130 - Sàrl. capital 152K - Siren 414 997 130 R.C.S. Bourg - APE 332B
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