GS1535B Gennum Corporation, GS1535B Datasheet - Page 18

• Manufacturer Part Number: GS1535B
• Description: Multi-rate Sdi Automatic Reclocker
• Manufacturer: Gennum Corporation

4.2 VCO
4.3 Charge Pump
The S-PLL offers several advantages over the linear PLL. The Loop Bandwidth of
an S-PLL is independent of the transition density of the input data. Pseudo-random
data has a transition density of 0.5 verses a pathological signal which has a
transition density of 0.05. The loop bandwidth of a linear PLL will change
proportionally with this change in transition density. With an S-PLL, the loop
bandwidth is defined by the jitter at the data input. This translates to infinite loop
bandwidth with a zero jitter input signal. This allows the loop to correct for small
variations in the input jitter quickly, resulting in very low output jitter. The loop
bandwidth of the GS1535B/9065B’s PLL is defined at 0.2UI of input jitter.
The PLL consists of two acquisition loops. First is the Frequency Acquisition (FA)
loop. This loop is active when the device is not locked and is used to achieve lock
to the supported data rates. Second is the phase acquisition (PA) loop. Once
locked, the PA loop tracks the incoming data and makes phased corrections to
produce a re-clocked output.
The internal VCO of the GS1535B/9065B is a ring oscillator. It is trimmed at the
time of manufacture to capture all data rates over temperature and operation
voltage ranges.
Integrated into the VCO is a series of programmable dividers used to achieve all
serial data rates, as well as additional dividers for the frequency acquisition loop.
A common charge pump is used for the PLL of the GS1535B/9065B.
During frequency acquisition, the charge pump has two states, “pump-up” and
“pump-down,” which is produced by a leading or lagging phase difference between
the input and the VCO frequency.
During phase acquisition, there are two levels of “pump-up” and two levels of
“pump down” produced for leading and lagging phase difference between the input
and VCO frequency. This is to allow for greater precision of VCO control.
The charge pump produces these signals by holding the integrated frequency
information on the external loop-filter capacitor, C
information is the result of the current flowing through an internal resistor
connected to the loop-filter capacitor.
40066 - 0
August 2006
GS1535B / GS9065B Preliminary Data Sheet
LF
. The instantaneous frequency
18 of 27