GENNUM CORPORATION P.O. Box 489, Stn. A, Burlington, Ontario, Canada L7R 3Y3
Tel. +1 (905) 632-2996 Fax. +1 (905) 632-5946 E-mail: info@gennum.com
www.gennum.com
Revision Date: March 2000
Document No. 522 - 02 - 03
PRELIMINARY DATA SHEET
G
S
1
508
HD-LINX
TM
GS1508
HDTV Cable Driver
FEATURES
SMPTE 292M compliant
dual cable driving outputs optimized for driving data
up to 1.485Gb/s
7% tolerance output
>17dB output return loss
minimum external components
seamless interface with the HD-LINXTM family of
products
low power
standard packaging
APPLICATIONS
1.485Gb/s HDTV Serial Digital Receiver Interfaces for:
Routers, Distribution Amplifiers, Switchers, and other
transmitting equipment.
DESCRIPTION
The GS1508 is a first generation very high speed bipolar
integrated circuit designed to drive two 75
co-axial
cables. The GS1508 is a SMPTE 292M compliant cable
driver that directly interfaces with other Gennum HDTV
devices and can also be used as a general purpose high
speed cable driver.
The GS1508 features two complementary outputs whose
amplitude is controlled within a precise 7% variation. The
output amplitude can be varied by adjusting the R
SET
resistor value.
The serial inputs can be AC coupled. The GS1508 is a low
power device that does not require external pull down
resistors. The GS1508 is packaged in an 8 pin SOIC and
operates from a single 5V power supply.
BLOCK DIAGRAM
ORDERING INFORMATION
PART NUMBER
PACKAGE
TEMPERATURE
GS1508-CKA
8 pin SOIC
0C to 70C
GS1508-CTA
8 pin Tape and Reel
0C to 70C
SDO
R
SET
SDO
SDI
SDI
BANDGAP REFERENCE AND BIASING CIRCUIT
OUTPUT STAGE &
CONTROL
INPUT
DIFFERENTIAL
PAIR
PATENT PENDING
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2
G
S
150
8
ABSOLUTE MAXIMUM RATINGS
T
A
= 25C unless otherwise indicated
PARAMETER
VALUE
Supply Voltage
5.5V
Input Voltage Range (any input)
-0.3 to (V
CC
+0.3)V
Operating Temperature Range
0C to 70C
Storage Temperature
-65C to 150C
Power Dissipation
300mW
Lead Temperature (soldering, 10 sec)
260C
Input ESD Voltage
2000V
DC ELECTRICAL CHARACTERISTICS
V
CC
= 5V, T
A
= 0C to 70C unless otherwise shown.
Specifications assume 800mV output amplitude level settings into end terminated 75
transmission lines. Data Rate = 1485Mb/s unless otherwise shown.
PARAMETER
CONDITIONS
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
TEST
LEVEL
Supply Voltage
V
CC
4.75
5.00
5.25
V
1
System Power
Consumption
Driving two
75
cables
P
D
-
215
265
mW
1
Supply Current
I
S
-
43
54
mA
1
Common Mode Input
Voltage Range
V
CM,IN
2.5+(V
DIFF/2
)
-
V
CC
-(V
DIFF/2
)
V
2
Common Mode Output
Voltage Range
V
CM,OUT
-
V
CC
-V
OUT
-
V
2
AC ELECTRICAL CHARACTERISTICS
V
CC
= 5V, T
A
= 0C to 70C unless otherwise shown.
Specifications assume 800mV output amplitude levels into end terminated 75
transmission lines. Data Rate = 1485Mb/s unless otherwise shown.
PARAMETER
CONDITIONS
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
TEST
LEVEL
Serial Digital Rate
DC
1485
-
Mb/s
1
Additive Jitter
1485Mb/s
-
5
-
ps
RMS
1
3
Differential Input
V
DIFF
150
-
800
mV
diff p-p
2
Differential Output
V
OUT
750
800
850
mV
p-p
1
Output Rise/Fall Times
(20% - 80%)
t
R
, t
F
-
120
250
ps
2
1
Mismatch in Output Rise/Fall
Times
-
15
30
ps
4
Overshoot
-
1
8
%
4
Duty Cycle Distortion
-
15
30
ps
1
Output Return Loss
5MHz to 1485MHz
-
17
-
dB
2
4
NOTES:
1. RMS additive jitter measured using Pseudo Random bit sequence (2
23
- 1).
2. Measured with Gennum Evaluation Board (EB1508).
TEST LEVELS:
1. 100% tested at 25C.
2. Guaranteed by design.
3. Correlated Value.
4. Tested with EB1508
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3
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S
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508
PIN CONNECTIONS
INPUT / OUTPUT CIRCUITS
Fig. 1 (Pins 1 and 2)
Fig. 2 (Pins 7 and 8)
SDI
SDI
V
EE
R
SET
SDO
SDO
GND
V
CC
1
2
3
4
8
7
6
5
GS1508
TOP
VIEW
PIN DESCRIPTIONS
NUMBER
SYMBOL
TYPE
DESCRIPTION
1, 2
SDI, SDI
I
Serial data inputs (non-inverting and inverting).
3
V
EE
P
Most negative supply voltage.
4
R
SET
I
Output amplitude control resistor.
5
V
CC
P
Most positive supply voltage.
6
GND
P
Not connected internally. Connect to Ground. Used for isolation.
7, 8
SDO, SDO
O
Serial data outputs (non-inverting and inverting).
SDI
V
CC
SDI
5k
20k
R
SET
SDO SDO
+
-
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4
G
S
150
8
DETAILED DESCRIPTION
INPUT INTERFACING
SDI/SDI are high impedance differential inputs. (
See
Figure 1 for equivalent input circuit).
Several conditions must be observed when interfacing to
these inputs:
1. The differential input signal amplitude must be between
150 and 800mVpp.
2. The common mode voltage range must be as specified
in the DC Characteristics table. For a 400mV input from
the GS1504 HD cable equalizer, this corresponds to a
common mode voltage range of between 2.7 and 4.8
volts.
3. For input trace lengths longer than approximately 1cm,
the inputs should be terminated as shown in the Typical
Application Circuit.
The GS1508 inputs are self biased, allowing for simple AC
coupling to the device. For serial digital HDTV, a minimum
capacitor value of 4.7F should be used to allow coupling
of pathological test signals. A tantalum capacitor is
recommended.
OUTPUT INTERFACING
The GS1508 outputs are current mode, and will drive
800mV into a 75 ohm load. These outputs are protected
from accidental static damage with internal static protection
diodes.
The SMPTE 292M standard requires that the output of a
cable driver have a source impedance of 75
and a return
loss of at least 15dB between 5Mhz and 1.485GHz.
In order for an HD SDI output circuit using the GS1508 to
meet this specification, the output circuit shown in the
Typical Application Circuit is recommended.
The values of L
COMP
and C
COMP
will vary depending on PCB
layout, but typical values are 12nH and 0.5pF respectively.
The small value of C
COMP
can be easily swamped by
parasitic PCB capacitance, so it is recommended that the
ground plane be removed under the GS1508 output
circuitry (
see the Application Information section in this data
sheet for further details). A 4.7F capacitor is used for AC
coupling the output of the GS1508. This value is chosen to
ensure that pathological signals can be coupled without a
significant DC component occurring.
Fig. 3 Output Optimized for Waveform Symmetry
L=8.2nH, R=75 (Typical ORL=13.5dB)
Fig. 4 Output Optimized for Return Loss
L=12nH, C=0.5pF, R=75 (Typical ORL=18dB)
Figures 3 and 4 show the eye diagram of the GS1508
output for two different output compensation conditions.
Figure 4 shows the GS1508 output optimized for wideband
return loss of 18dB. Figure 3 shows the GS1508 output
optimized for output waveform symmetry. In this case the
output may not exhibit a return loss of 15dB.
When measuring return loss at the GS1508 output it is
necessary to take the measurement for both a logic high
and a logic low output condition. This is because the output
protection diodes act as a varactor (voltage controlled
capacitor) as shown in Figure 5.
Consequently, the output capacitance of the GS1508 is
dependent on the logic state of the output.
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5
G
S
1
508
Fig. 5 Static Protection Diodes
OUTPUT RETURN LOSS MEASUREMENT
To perform a practical return loss measurement, it is
necessary to force the GS1508 output to a DC high or low
condition. The actual measured return loss will be based on
the outputs being static at V
CC
or V
CC
-1.6V. Under normal
operating conditions the outputs of the GS1508 swing
between V
CC
-0.4V and V
CC
-1.2V, so the measured value of
return loss will not represent the actual operating return
loss.
A simple method of calculating the values of actual
operating return loss is to interpolate the two return loss
measurements. In this way, the values of return loss are
estimated at V
CC
-0.4V and V
CC
-1.2V based on the
measurements at V
CC
and V
CC
-1.6V.
The two values of return loss (high and low) will typically
differ by several decibels. If the measured return loss is R
H
for logic high and R
L
for logic low, then the two values can
be interpolated as follows:
R
IH
= R
H
- (R
H
-R
L
)/4 and
R
IL
= R
L
+(R
H
-R
L
)/4
where R
IH
is the interpolated logic high value and R
IL
is the
interpolated logic low value.
For example, if R
H
= -18dB and R
L
= -14dB, then the
interpolated values are R
IH
= -17dB and R
IL
= -15dB.
OUTPUT AMPLITUDE ADJUSTMENT
The output amplitude of the GS1508 can be adjusted by
changing the value of the R
SET
resistor as shown in Figure 6
and Table 1. For an 800mV
p-p
output with a nominal 7%
tolerance, a value of 53.6% is required. A 1% SMT resistor
should be used.
The R
SET
resistor is part of the high speed output circuit of
the GS1508. The resistor should be placed as close as
possible to the R
SET
pin. In addition, PCB capacitance
should be minimized at this node by removing the PCB
groundplane beneath the R
SET
resistor and the R
SET
pin.
Fig. 6 GS1508 Output Amplitude vs. 1/R
SET
NOTE: For reliable operation of the GS1508 over the full
temperature range, do not use an R
SET
value below 49.9
.
SDO
SDO
GS1508
TABLE 1: R
SET
vs V
OUT
R
SET
R
1/R
SET
OUTPUT SWING
500.0
0.0020
0.095
150.0
0.0067
0.298
75.0
0.0133
0.575
53.6
0.0187
0.785
43.2
0.0231
0.937
1.000
0.800
0.600
0.400
0.200
0.000
0.0000 0.0050 0.0100 0.0150 0.0200 0.0250
1 / R
SET
(mho)
OUTPUT SWING
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