E142AHF Datasheet, PDF (6/19 Pages) Semtech Corporation – Per Pin timing Deskew w 4x2 Cross Point Switch

Edge142
EDGE HIGH-PERFORMANCE PRODUCTS
Circuit Description (continued)
Falling Edge Adjust
Default Conditions
VFALL allows independent adjustment of the falling edge
(see Figure 3). The propagation delay for a falling edge
is defined as
Tpd- = Tpd(nom) + Tspan + Tfall
where Tfall is defined as the additional delay incurred by
adjusting the VFALL input. Notice that Tfall can be either
positive or negative over a ± 150 ps range, depending
on where VMID is set. This flexibility allows the part to
either expand or contract an input signal .
All digital inputs have either an internal pull up (to ground)
or pull down (to VEE) resistor (~50 KΩ) to protect against
floating inputs migrating to an indeterminant state. All
differential timing inputs are pulled to a logical zero state.
All operating mode control inputs are pulled down to a
logical zero. The mux select and mux enable inputs
have pull down resistors to VEE. And the output enable
is pulled up to ground.
The following chart summarizes the internal state of the
digital inputs.
Notice also that Tpd+ is a function of VDELAY only, while
Tpd- is a function of VDELAY and VFALL. The transfer
function for Tspan vs. VDELAY is shown in Figure 4. The
transfer function for Tfall vs. VFALL is shown in Figure 5.
VMID
VMID is used in conjuction with VFALL to remove any
systematic pulse width expansion or contraction. VMID
and VFALL are differential analog voltage inputs which
affect the falling edge delay.
Input
Internal Resistor
IN0, IN1, IN2, IN3
Pull Down to VEE
IN0*, IN1*, IN2*, IN3* Pull up to GND
S00, S10, S01, S11 Pull Down to VEE
MUX0 SEL, MUX1 SEL Pull Down to VEE
MUX EN
Pull Down to VEE
EN*
Pull up to GND
When VFALL equals VMID, there will be no programmed
pulse width variation between the input and the output
signal. It is the difference between VMID and VFALL
that expands or contracts a pulse.
However, despite the internal resistors providing a known
default condition, it is recommended that no unused
inputs be left floating.
VMID should be statically established at the midpoint of
the voltage swing of VFALL.
INPUT
Programming Sequence
VFALL = +0.1V
VFALL = –1.3V
VDELAY, in addition to affecting the placement of the
rising edge, also affects the falling edge. Therefore, when
calibrating a system, VDELAY should be adjusted first.
As VFALL affects only the falling edge, it should be
adjusted after VDELAY is established.
OUTPUT
(–1.3V < VDELAY < +0.1V)
TPDmin + Tspan
TPDmin + Tspan + Tfall
Figure 3. Falling Edge Control
 2000 Semtech Corp.
6
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