gs9005a Gennum Corporation, gs9005a Datasheet - Page 10

• Manufacturer Part Number: gs9005a
• Description: Serial Digital Receiver Corporation
• Manufacturer: Gennum Corporation

520 - 28 - 11
VCO Frequency Setting Resistors
There are two modes of VCO operation available in the
GS9005A. 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) may be used for any data rate 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 GS9005A.
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.
INPUT
22n
75
75
2
1
113
-5V
47p
-5V
47p
VCO
0.1
resistance is approximately
-5V
ECL
DATA
INPUTS
Fig. 17 GS9005A Typical Test Circuit Using -5V Supply
STAR
ROUTED
+
10
11
-5V
5
6
7
8
9
10
5.6p
10n
DDI
DDI
VCC2
SDI
SDI
ƒ/2
VEE3
0.1
0.1
12 13 14 15 16 17 18
LOOP
VOLTAGE
910
4
GS9005A
3
2
All resistors in ohms, all capacitors in microfarads, all inductors in henries unless otherwise stated.
1 28 27 26
SSI
10
-5V
See Figure 18
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.
SDO
SDO
SCO
SCO
SS1
SS0
-5V
CD
-5V
0.1
25
24
23
22
21
20
19
0.1
10k
-5V
ANALOG
DIGITAL
390
100
390
390
100
100
390
100
CLOCK
DATA
CLOCK
CARRIER
DETECT
OUTPUT
DATA
-5V