GS2970 Datasheet, PDF (30/145 Pages) Semtech Corporation – 3Gb/s, HD, SD SDI Receiver Complete with SMPTE Audio and Video Processing

The SDO output is muted when the RC_BYP pin is set HIGH and the PLL is unlocked
(LOCKED pin is LOW). When muted, the output is held static at logic ‘0’ or logic ‘1’.
Table 4-1: Serial Digital Output
SDO_EN/DIS
0
1
1
RC_BYP
X
1
0
SDO/SDO
Disabled
Re-timed
Buffered (not re-timed)
NOTE: the serial digital output is muted when the GS2970 is unlocked.
4.5 Serial Digital Reclocker
The GS2970 includes both a PLL stage and a sampling stage.
The PLL is comprised of two distinct loops:
• A coarse frequency acquisition loop sets the centre frequency of the integrated
Voltage Controlled Oscillator (VCO) using an external 27MHz reference clock
• A fine frequency and phase locked loop aligns the VCO’s phase and frequency to
the input serial digital stream
The frequency lock loop results in a very fast lock time.
The sampling stage re-times the serial digital input with the locked VCO clock. This
generates a clean serial digital stream, which may be output on the SDO/SDO output
pins and converted to parallel data for further processing. Parallel data is not affected by
RC_BYP. Only the SDO is affected by this pin.
4.5.1 PLL Loop Bandwidth
The fine frequency and phase lock loop in the GS2970 reclocker is non-linear. The PLL
loop bandwidth scales with the jitter amplitude of the input data stream; automatically
reduces bandwidth in response to higher jitter. This allows the PLL to reject more of the
jitter in the input data stream and produce a very clean reclocked output.
The loop bandwidth of the GS2970 PLL is defined with 0.2UI input jitter. The bandwidth
is controlled by the LB_CONT pin. Under nominal conditions, with the LB_CONT pin
floating and 0.2UI input jitter applied, the loop bandwidth is set to 1/1000 of the
frequency of the input data stream. Connecting the LB_CONT pin to 3.3V reduces the
bandwidth to half of the nominal setting. Connecting the LB_CONT pin to GND increases
the bandwidth to double the nominal setting. Table 4-2 below summarizes this
information.
GS2970 3Gb/s, HD, SD SDI Receiver Complete with
SMPTE Audio and Video Processing
Data Sheet
47478 - 4
September 2012
30 of 145