GS1575B / GS9075B HD-LINX® II Multi-Rate SDI

Automatic Reclocker

Data Sheet

40063 - 1

June 2009

17 of 28

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 GS1575B/9075B’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.

4.2 VCO

The internal VCO of the GS1575B/9075B 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.

4.3 Charge Pump

A common charge pump is used for the PLL of the GS1575B/9075B.

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 is the result of the current flowing through an internal resistor connected to

the loop-filter capacitor.