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The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) Page 25 of 25
F
IGURE
3.24
B
: S
IGNAL TRACES OF INPUT SIGNALS
. U
PPER TRACE
:
AS SUPPLIED TO THE
CFD’
S
I
N SOCKET
(
OBTAINED FROM
AN ALTERNATIVE AMPLIFIER OUTPUT
),
LOWER TRACE
:
RAMP MONITOR OUTPUT
(
THE
R
AMP SWITCH IS TURNED OFF
HERE
). S
IGNALS ARE TRIGGERED ON THE
CFD
TIMING OUTPUT SIGNAL
(
TRACE NOT SHOWN
). L
EFT AND RIGHT
PICTURES WERE OBTAINED WITH TWO DIFFERENT CABLE LENGTHS BETWEEN
A
IN
AND
A
OUT
SOCKETS
.......................... 20
F
IGURE
3.25
B
: S
IGNAL TRACES TRIGGERED ON
CFD
TIMING SIGNAL
. U
PPER TRACE
:
INPUT SIGNAL
(
AS IN
F
IGURE
3.24
B
),
LOWER TRACE
:
RAMP MONITOR OUTPUTS WITH
R
AMP SWITCH TURNED ON
. L
EFT PICTURE
: “
PURE
”
RAMP SIGNAL
(
OBTAINED WITHOUT SIGNAL INPUT TO ON
A
IN
SOCKET
),
RIGHT
:
WITH SIGNAL CONNECTED TO
A
IN
(
NORMAL
OPERATION
) ................................................................................................................................................................. 21
F
IGURE
3.26
B
:
UPPER TRACE
: CFD
X OUTPUT
,
MIDDLE TRACE
:
STOP OUTPUT
(
WITH A PULSE WIDTH SET BY THE
S
TOP
W
IDTH
POTENTIOMETER SETTING
),
LOWER TRACE
:
RAMP MONITOR
,
ALL TRACES TRIGGERED ON THE STOP SIGNAL
. T
HE STOP
SIGNAL SHOULD BE USED IF THERE IS A SPARE
TDC
CHANNEL AVAILABLE
................................................................. 21
F
IGURE
3.27
B
:
AS
F
IGURE
3.25
B RIGHT
,
BUT INCLUDING THE
CFD
X OUTPUT
(
LOWEST TRACE
)
FOR THREE DIFFERENT
SETTING OF THE
“
WIDTH OFFSET
”
POTI
. T
HE PULSE
-
HEIGHT
/
DELAY RATIO IS NOT AFFECTED BY CHANGING THIS
SETTING
,
ONLY THE DELAY OFFSET AT ZERO PULSE HEIGHT
. T
HE MIDDLE PICTURE SHOWS A TYPICAL SETTING
,
IN THE
LEFT PICTURE THE SETTING IS OPTIMIZED FOR LOW DEAD
-
TIME
(
REQUIRES A MULTI
-
TRANSITION
TDC
WITH LOW DEAD
TIME
). I
N THE RIGHT PICTURE THE OFFSET IS SET TOO HIGH
,
INDICATED BY A FLAT BASE AT THE END OF THE SIGNAL
(
MARKED IN RED
): T
HE CIRCUIT WILL NOT FUNCTION PROPERLY IN THIS CONDITION
.................................................. 22
F
IGURE
3.28
B
: L
IN AND LOG PLOTS OF THE PULSE HEIGHT DISTRIBUTION FROM A MICRO
-
CHANNEL PLATE AS OBTAINED
WITH A
CFD1
X UNIT
. T
HE PEAK FOR PULSE HEIGHT ZERO IN THE LOG PLOT
(
SEE ARROW
)
WAS OBTAINED BY
TEMPORARILY REMOVING THE INPUT TO
A
IN
DURING DATA ACQUISITION
(
SITUATION AS IN
F
IGURE
3.25
B LEFT
) ........ 22
List of Equations
E
QUATION
3.1
B
................................................................................................................................................................... 11