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Application Brief

BAW Oscillator Solutions for Network Interface Card

Juan Rodriguez

Clock and Timing Solutions

BAW Resonator Technology

BAW Oscillator in Network Interface Card

Bulk Acoustic Wave (BAW) is a micro-resonator
technology that enables the integration of highprecision and ultra-low jitter clocks directly intopackages that contain other circuits. In the BAW
oscillator, the BAW is integrated with a colocatedprecision temperature sensor, a ultra-low jitter, lowpower fractional output divider (FOD), a singleended LVCMOS and differential LVPECL, LVDS, andHCSL output driver, and a small power-reset-clock
management system consisting of several low-noise
low dropout (LDOs) regulators..

Some SmartNICs implement a common clock andindependent reference PCIe clocking architecture at
the same time. The card receives a clock from themotherboard through a PCIe connector. Additionally,
the card needs a PCIe clock source in the casethe common clock from the connector is unavailable.
The PCIe buffer can be necessary since ASIC andFPGA typically needs more than one PCIe clock.
The LMK6H BAW oscillator can be used in Network
Interface Card (NIC) applications to clock the PCIe
buffer and MUX, as well as the Ethernet buffer, whichis shown in Figure 2.

Figure 1 shows the structure of the BAW resonator
technology. The structure includes a thin layer ofpiezoelectric film sandwiched between metal films
and other layers that confine the mechanical energy.
The BAW utilizes this piezoelectric transduction togenerate a vibration.

Every NIC or SmartNIC require an Ethernet oscillator,
which can require precise jitter performance. TI's
current design, the LMK6H, LMK6P, and LMK6Dprovides 125 fs maximum at 156.25 MHz (12k- 20M).
This Ethernet oscillator serves as the clock source
for the Ethernet buffer. The LP-HCSL buffers that areused in PCIe meet the requirements for the Ethernet
clock fan-out, that being the CDCDB family.

Figure 1. Basic Structure of a Bulk Acoustic Wave (BAW) Resonator

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PCIe clock from connector
2:x PCIe MUX

100 MHz HCSL
PCIe Oscillator
LMK6H156.25 MHz
Ethernet Oscillator
LMK6H/P/D,

1:4/8/20 PCIe buffer
CDCDB400/800/2000

ASIC/FGPA
Integrated Processor,SerDes, Retimer
1:4/8/20 Ethernet buffer
CDCDB400/800/2000

Figure 2. Typical SmartNIC Clock Tree
Benefits of the BAW Oscillator
One of the key benefits of the BAW oscillator
in comparison to microelectromechanical systems(MEMs) and quartz oscillators is the exceptional jitter
performance. Figure 4 shows the jitter performance
for TI's BAW oscillator design.
TI’s BAW oscillator family supports 1.8-V, 2.5-V, and3.3-V supply voltages and is available in DLE (3.2mm × 2.5 mm) and DLF (2.5 mm × 2 mm) packages,
which save space in compact board designs. Figure 3
showcases the two BAW oscillator layouts on the left
in comparison to both a typical crystal layout, and acrystal with BAW oscillator combination.

The BAW oscillator is tolerant to temperatures up
to 105°C and features a 20 to 30 higher MeanTime Before Failure (MTBF) than competing crystal
oscillator designs. Figure 5 shows that through thelifetime of the BAW oscillator, it has a reliablefrequency stability of ±25 ppm, inclusive of all aging
and environmental factors. Over temperature, theBAW oscillator has a ±10 ppm frequency stability
that is significantly better than current quartz-based
oscillators.
Figure 6 shows the vibration sensitivity of the BAW
oscillator. The BAW oscillator has a typical vibration
sensitivity of 1 ppb/g, which is significantly better than
the 5–10 ppb/g sensitivity of quartz oscillator designs.

Figure 3. PCB Footprint Comparison of BAW Oscillator and Crystal

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Figure 4. BAW Oscillator 156.25-MHz Phase-Noise Performance (Normalized Spur Mode)

Figure 5. BAW Oscillator vs Quartz XO: Frequency Stability Over Temperature

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Figure 6. Vibration Sensitivity Comparison of BAW Oscillator and Quartz

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