e7765 Semtech Corporation, e7765 Datasheet - Page 6

• Manufacturer Part Number: e7765
• Description: 1.3 Ghz Quad Pin Electronics Driver
• Manufacturer: Semtech Corporation

Driv
Driv
Do NO
Do NO
Do NO
Do NO
Driv
Driver er er er er
Driv
The driver digital control inputs DHI/DHI* and DEN/DEN*
are “Flex Inputs” – wide voltage differential inputs capable
of receiving ECL, TTL, CMOS, or custom level signals.
Single-ended operation is supported by connecting the non-
driven, differential input to the appropriate DC threshold
level. Differential input drive is recommended for highest
performance.
Drive Enable
The drive enable inputs (DEN / DEN*) control whether the
driver is forcing a voltage, or is placed in a high-imped-
ance state. If DEN is more positive than DEN*, the output
will force either DVH or DVL. If DEN is more negative than
DEN*, the output goes into a high impedance state. The
DEN/DEN* inputs are independent per drive channel and
remain effective in the differential mode.
Do NO
Do NOT lea
Do NO
Driver Data
When the driver is enabled (Table 1) the drive data inputs
(DHI / DHI*) determine whether the driver output is forc-
ing a high or a low. If DHI is more positive than DHI*, the
driver will force DVH when the driver is active. If DHI is
more negative than DHI*, the driver will force DVL when
active. The DHI/DHI* inputs are independent per drive
channel, but these input signals for drive channels 1 and
3 are not effective when differential mode is enabled.
Do NO
Do NO
Do NOT lea
Driver Differential Mode Selection
The TTL input SEL_DHI will place a pair of drive channels
into a differential drive mode. Channels 0 and 1 are a
differential pair that is independent from the channel 2
and 3 differential pair.
Circuit Description (continued)
TEST AND MEASUREMENT PRODUCTS
©
2006 Semtech Corp. , Rev. 11, 7/18/06
S
T lea
T lea
T lea
T lea
T lea
T leav v v v v e DEN / DEN* floating.
T lea
T leav v v v v e DHI / DHI* floating.
E
L
_
0
D
1
H
e DEN / DEN* floating.
e DEN / DEN* floating.
e DEN / DEN* floating.
e DEN / DEN* floating.
e DHI / DHI* floating.
e DHI / DHI* floating.
e DHI / DHI* floating.
e DHI / DHI* floating.
[ I
] 0
D
D
D
H
I H
I H
0 [
D /
D /
f ]
H
H
o r
[ * I
[ * I
m
] 0
] 0
:
D
D
D
H
I H
H
1 [
* I
D /
D /
f ]
H
H
o r
[ * I
[ I
m
] 1
] 0
:
6
SEL_DHI[0] = 1 is used for outputting a differential signal
where DOUT[1] is the inverse of DOUT[0] with the mini-
mum of skew, and both drivers respond to the DHI/DHI*[0]
signal. More detail is shown in Table 2. Notice that power-
on (PON) and drive enable (DEN) controls are all still in
effect for individual drivers. SEL_DHI[1] likewise controls
the second pair, channels 2 and 3.
Driver Levels
DVH and DVL are high input impedance voltage inputs
which establish the driver’s high and low output levels.
Driver Bias
The DBIAS pin is an analog current input which establishes
an on-chip bias current, from which other currents are
generated. This current, to some degree, also establishes
the overall power consumption and performance of the
drivers. Each driver is given its own DBIAS control to allow
for varying performance among the four drivers.
Ideally, an adjustable external current source would be
used to minimize any part-to-part performance variation
within a test system. However, a precision external resis-
tor tied to a large positive voltage is typically acceptable.
(See figure below.) The optimal DBIAS current is a func-
tion of the RADJ and FADJ settings, and cannot be set in-
dependently.
The established bias current follows the equation:
DBIAS = (VCC - 0.7) / (Rext + 462 ).
BIAS
VEE
462Ω
Rext
VCC
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E7765