GS3470 datasheet(27/169 Pages) SEMTECH

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GS3470

Final Data Sheet

Rev.8

PDS-060500

September 2017

27 of 169

Semtech

www.semtech.com

4.6 Serial Digital Retimer

The retimer operates at three frequencies: 2.97Gb/s, 1.485Gb/s, and 270Mb/s.

Note: The SD/HD bit takes precedence over the 3G/HD bit, so if the SD/HD bit is HIGH,

the 3G/HD bit is ignored.

The retimer can automatically determine the supported rate based on the input signal,

or the rate can be set manually. For more detail on these modes, please refer to

Section 4.3.1.

4.7 External Crystal/Reference Clock

The GS3470 requires an external 27MHz reference clock for correct operation. This

reference clock is generated by connecting a crystal to the XTAL and XTAL pins of the

device. Refer to Typical Application Circuit.

A crystal with a maximum frequency variation of ±100ppm and a maximum equivalent

resistance of 50Ω should be selected.The external crystal is used in the frequency

acquisition process. It has no impact on the output jitter performance of the device

when the device is locked to incoming data.

Alternately, a 27MHz external clock source can be connected to the XTAL pin of the

device. It is recommended to DC-couple the reference clock input and to ensure the

reference clock does not exceed 1.2V.

4.8 Lock Detect

The LOCKED output signal is set HIGH by the Lock Detect block under the following

conditions:

Table 4-3: Serial Digital Output

SERIAL_LOOPBACK_EN

RC_BYP

DDO/DDO

Disabled

Re-timed

Buffered (not Re-timed)

Table 4-4: Lock Detect Conditions

Mode of Operation

Mode Setting

Condition for Locked

SMPTE Mode

SMPTE_BYPASS = HIGH

DVB_ASI = LOW

Retimer PLL is locked to valid

SMPTE video.

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