GS9028
The termination resistor (R
T
) value should be equal to the
characteristic impedance of the cable. Controlled
impedance traces should be used for the outputs and the
termination resistors should be placed near the GS9028.
The inductor (L) and resistor (R) are used to optimize the
output return loss and are PCB dependent. Typically, R
equals the transmission line characteristic impedance and
L is approximately 8.2nH.
OUTPUT AMPLITUDE ADJUSTMENT
The GS9028 outputs are adjustable from as low as 50mV to
as high as 1000mV. The output amplitude is set by the R
SET
resistor connected to pin 4. The relationship between the
output amplitude (V
OUT
) and R
SET
is approximately given by
the equation below:
R
SET
= (1.3696 x Z
O
)/(2 x V
OUT
) - 5.5
where Z
O
is in ohms and V
OUT
is in volts.
The minimum value of R
SET
is 46Ω. For 75Ω cable and
800mV output amplitudes, the value of R
SET
is 59Ω. Also,
note that the above formula assumes that the transmission
line is properly end terminated.
TYPICAL APPLICATION CIRCUIT
5
6
7
8
V
EE
SDI
GS9028
SDI
V
CC
SDO
1
SDO
8.2nH
75
75
75
1µ
8.2nH
4
R
SET
3
V
EE
2
1µ
59
75
1µ
100n
V
CC
10n
V
CC
All resistors in ohms, all capacitors in farads, unless otherwise shown.
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GENNUM [ GENNUM CORPORATION ]
