LMK04000 Datasheet, PDF (1/54 Pages) National Semiconductor (TI) – Low-Noise Clock Jitter Cleaner with Cascaded PLLs

LMK04000 Family
September 10, 2010
Low-Noise Clock Jitter Cleaner with Cascaded PLLs
1.0 General Description
The LMK04000 family of precision clock conditioners pro-
vides low-noise jitter cleaning, clock multiplication and distri-
bution without the need for high-performance voltage con-
trolled crystal oscillators (VCXO) module. Using a cascaded
PLLatinum™ architecture combined with an external crystal
and varactor diode, the LMK04000 family provides sub-200
femtosecond (fs) root mean square (RMS) jitter performance.
The cascaded architecture consists of two high-performance
phase-locked loops (PLL), a low-noise crystal oscillator cir-
cuit, and a high-performance voltage controlled oscillator
(VCO). The first PLL (PLL1) provides a low-noise jitter cleaner
function while the second PLL (PLL2) performs the clock gen-
eration. PLL1 can be configured to either work with an exter-
nal VCXO module or use the integrated crystal oscillator with
an external crystal and a varactor diode. When used with a
very narrow loop bandwidth, PLL1 uses the superior close-in
phase noise (offsets below 50 kHz) of the VCXO module or
the crystal to clean the input clock. The output of PLL1 is used
as the clean input reference to PLL2 where it locks the inte-
grated VCO. The loop bandwidth of PLL2 can be optimized
to clean the far-out phase noise (offsets above 50 kHz) where
the integrated VCO outperforms the VCXO module or crystal
used in PLL1.
The LMK04000 family features dual redundant inputs, five
differential outputs, and an optional default-clock upon power
up. The input block is equipped with loss of signal detection
and automatic or manual selection of the reference clock.
Each clock output consists of a programmable divider, a
phase synchronization circuit, a programmable delay, and an
LVDS, LVPECL, or LVCMOS output buffer. The default start-
up clock is available on CLKout2 and it can be used to provide
an initial clock for the field-programmable gate array (FPGA)
or microcontroller that programs the jitter cleaner during the
system power up sequence.
2.0 Features
■ ^{Cascaded PLLatinum PLL Architecture}
— PLL1
■ ^{Phase detector rate of up to 40 MHz}
■ ^{Integrated Low-Noise Crystal Oscillator Circuit}
■ ^{Dual redundant input reference clock with LOS}
— PLL2
■ ^{Normalized [1 Hz] PLL noise floor of -224 dBc/Hz}
■ ^{Phase detector rate up to 100 MHz}
■ ^{Input frequency-doubler}
■ ^{Integrated Low-Noise VCO}
■ ^{Ultra-Low RMS Jitter Performance}
— 150 fs RMS jitter (12 kHz – 20 MHz)
— 200 fs RMS jitter (100 Hz – 20 MHz)
■ ^{LVPECL/2VPECL, LVDS, and LVCMOS outputs}
■ ^{Support clock rates up to 1080 MHz}
■ ^{Default Clock Output (CLKout2) at power up}
■ ^{Five dedicated channel divider and delay blocks}
■ ^{Pin compatible family of clocking devices}
■ ^{Industrial Temperature Range: -40 to 85 °C}
■ ^{3.15 V to 3.45 V operation}
■ ^{Package: 48 pin LLP (7.0 x 7.0 x 0.8 mm)}
3.0 Target Applications
■ ^{Data Converter Clocking}
■ ^{Wireless Infrastructure}
■ ^{Networking, SONET/SDH, DSLAM}
■ ^Medical
■ ^{Military / Aerospace}
■ ^{Test and Measurement}
■ ^Video
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