GS9028 datasheet(6/7 Pages) GENNUM

6 / 7 page

521 - 68 - 04

The termination resistor (RT) value should be equal to the

characteristic

impedance

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 RSET

resistor connected to pin 4. The relationship between the

output amplitude (VOUT) and RSET is approximately given by

the equation below:

RSET = (1.3696 x ZO)/(2 x VOUT) - 5.5

where ZO is in ohms and VOUT is in volts.

The minimum value of RSET is 46Ω. For 75Ω cable and

800mV output amplitudes, the value of RSET is 59Ω. Also,

note that the above formula assumes that the transmission

line is properly end terminated.

TYPICAL APPLICATION CIRCUIT

10n

8.2nH

1µ

100n

VCC

RSET

VEE

SDO

VEE

SDI

VCC

8.2nH

GS9028

All resistors in ohms, all capacitors in farads, unless otherwise shown.

GS9028 Datasheet(PDF) 6 Page - Gennum Corporation