GS12341 datasheet(20/109 Pages) SEMTECH

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GS12341

Final Data Sheet

Rev.1

PDS-061928

August 2019

20 of 109

Semtech

Proprietary & Confidential

www.semtech.com

Note: The parameters referred to within Section 4.3.1 to Section 4.3.2 are linked to their

respective registers in Table 4-3. For a complete list of registers and functions, please see

Section 5.

4.3.1 PLL Loop Bandwidth Control

The ratio of output peak-to-peak jitter to input peak-to-peak jitter of the Reclocker can

be represented by a low-pass jitter transfer function, with a bandwidth equal to the PLL

loop bandwidth. Although the default loop bandwidth settings for the GS12341

Reclocker are ideal for most SDI signals, the GS12341 allows the user to adjust the loop

bandwidth for each supported rate.

Registers 0x0A through 0x0C contain the following parameters which allow the user to

configure rate dependent loop bandwidth: CFG_PLL_LBW_12G, CFG_PLL_LBW_6G,

CFG_PLL_LBW_3G, CFG_PLL_LBW_HD, CFG_PLL_LBW_SD, and

CFG_PLL_LBW_MADI. The loop bandwidth settings are defined in terms of ratios of the

nominal loop bandwidth. For each rate, where '1.0x' is the nominal loop bandwidth, the

following ratios are available: 0.0625x, 0.125x, 0.25x, 0.5x, and 1.0x. Table 2-3 provides

the specific loop bandwidths for each data rate and loop bandwidth setting. Lowering

the loop bandwidth will lower the jitter amplitude above the loop bandwidth

frequency. Although lower output jitter is desirable, the lower loop bandwidth may

reduce the device’s IJT to very high jitter that may be present outside the loop

bandwidth.

4.3.2 Automatic and Manual Rate Detection

With the default rate detect setting, the Reclocker will automatically attempt to lock to

any of following data rates: MADI (125Mb/s), SD-SDI (270Mb/s), HD-SDI (1.485Gb/s),

3G-SDI (2.97Gb/s), 6G-SDI (5.94Gb/s) and 12G-SDI (11.88Gb/s). This includes the f/1.001

rates. However, the Reclocker can be configured to only lock to a single rate, by setting

the CFG_AUTO_RATE_DETECT_ENA and CFG_MANUAL_RATE parameters in register

0x06.

The STAT_LOCK parameter in register 0x86 will indicate that the Reclocker is locked

when its value is 1b and unlocked when its value is 0b. The lock status can also be

monitored externally on any GPIO pin, however it is the default mode for GPIO1, pin 18.

The STAT_DETECTED_RATE parameter in register 0x87 will indicate the data rate at

which the Reclocker is locked to. A value of 0d in the STAT_DETECTED_RATE parameter

indicates that the device is not locked, while values between 1d and 6d will indicate that

the device is locked to one of the six available rates between MADI at 125Mb/s and

UHD-SDI at 11.88Gb/s.

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