10 of 10

32466 - 1

NOT

RECOMMENDED

FOR

NEW

DESIGNS

VCO Frequency Setting Resistors

There are two modes of VCO operation available in the

GS9005B. When the ƒ/2 ENABLE (pin 10) is LOW, any of the

four VCO frequency setting resistors, RVCO0 through RVCO3

(pins 13, 14, 15 and 17)maybeusedforanydatarate from 100

Mb/s to over 400 Mb/s. For example, for 143 Mb/s data

rate, the value of the total R

6k8 and for 270 Mb/s operation, the value is approximately

3k5. The 5k potentiometers will then tune the desired data

rate near their mid-points.

Jitter performance at the lower data rates (143, 177 Mb/s) is

improved by operating the VCO at twice the normal frequency.

This is accomplished by enabling the ƒ/2 function which

activates an additional divide by two block in the PLL section

of the GS9005B.

When the ƒ/2 ENABLE is HIGH two of the RVCO pins are

assigned to data rates below 200 Mb/s and two are assigned

to data rates over 200 Mb/s.

The selection is dependent upon the level of the STANDARD

SELECT BIT, SS1 (pin 21). When SS1 is LOW, RVCO0 and

RVCO1 (pins 13 and 14) are used for the higher data rates.

When SS1 is HIGH, the VCO frequency is now twice the bit rate

and its frequency is set by RVCO2 and RVCO3 (pins 15 and

17).

For 143 Mb/s and 270 Mb/s operation, (the VCO is at 286 MHz

and 270 MHz respectively) the total resistance required is

approximately the same for both data rates. This also applies

for 177 Mb/s and 360 Mb/s operation (the VCO is tuned

to 354 MHz and 360 MHz respectively). This means that one

potentiometer may be used for each frequency pair with only

a small variation of the fixed resistor value. This halves the

number of adjustments required.

Fig. 15 GS9005B Typical Test Circuit Using -5V Supply

All resistors in ohms, all capacitors in microfarads, all inductors in henries unless otherwise stated.

10µ

ECL

DATA

INPUTS

0.1µ

DATA

DATA

CLOCK

100

100

100

100

390

390

390

390

0.1µ

+

0.1µ

25

24

23

22

21

20

19

5

6

7

8

9

10

11

4

3 2

1 28 27 26

12 13 14 15 16 17 18

910

22n

75

113

75

47p

-5V

-5V

-5V

÷1

÷2

0.1µ

47p

0.1µ

-5V

10k

CARRIER

DETECT

OUTPUT

INPUT

GS9005B

DDI

DDI

VCC2

SDI

SDI

ƒ/2

VEE3

SDO

SDO

SCO

SCO

SS1

SS0

CD

SSI

LOOP

VOLTAGE

See Figure 18

ANALOG

DIGITAL

5.6p

-5V

-5V

-5V

-5V

-5V

10n

STAR

ROUTED

CLOCK