New parts leverage faster data rates of new PCIe standard

By Brian Santo, contributing writer

PCIe 4.0 version 1.0 was finally released late last year. More and more products that
conform to the spec are hitting the market, including a recent set of signal
switches, clock generators, and clock buffers from Diodes Inc. that support the
significantly faster operation of PCIe 4.0 buses. 

This latest iteration of the
Peripheral Component Interconnect Express (PCIe) bus standard has a number of
advances. But by far the most pertinent improvement is the doubling of data rates
compared to the preceding 3.0 revision (introduced in 2010), from 8
gigatransfers per second (GT/s) to 16 GT/s.

Revision 4.0 was originally due in 2015,
but it took PCI-SIG (which manages the PCI standards) 7 years to go from
revision 3.0 to revision 4.0. There are other buses, but the delay of PCIe 4.0 appears
to have encouraged the creation of yet one more standard, known as CCIX. PCI-SIG, apparently in response to CCIX, now plans
to introduce PCIe 5.0 in less than 2 years – in 2019. Version 5.0 will double
the transfer rate of PCIe yet again to 32 GT/s.

PCIe 4.0 will be immediately useful
for a variety of applications that thrive on speed, including gaming, high-performance
computing (HPC), and 10-Gigabit Ethernet connectors. PHYs, controllers and
FPGAs for PCIe 4.0 applications have been announced by PCI-SIG members such as
Cadence, Synopsys, IBM and Intel.

Most recently Diodes Inc. announced
its line of PCIe 4.0-compliant signal switches, clock generators and clock
buffers, which addresses “the expanding market for signal routing with
different protocols in PCs, servers, embedded applications including artificial
intelligence and fast data transfer generally,” said the company.

The PI3DBS16212 and PI3DBS16412 are 1-20 Gbits/s 2-channel and 4-channel 2:1
differential multiplexers/demultiplexers. The company said they are both
characterized by extremely low loss, reflection, crosstalk and skew. Typical
applications include switching high-speed serial signals employing a variety of
newer protocols. Specifically for PCIe 4.0 applications, the two muxes offer what
the company warrants as excellent signal integrity with an insertion loss of
just -1.3 dB at 16 Gbits/s. In this application, Diodes said, minimal skew
between channels eases the timing budget between nodes, and power dissipation
is very low (typically 300 µA).

The company also has four clock
generators aimed at various PCIe 4.0 applications. They are the PI6CG18201, PI6CG18401, PI6CG18801, and PI6CG15401. Based on the company’s own phase-locked loop
(PLL) design, they provide 1.8-V 2/4/8 HCSL outputs and 1.5-V 4 HCSL outputs,
respectively. All have jitter performance of less than 0.5 ps. They can provide
the reference clock for SERDES chipsets supporting the PCIe 4.0 interface. Each
output has its own enable with programmable slew rate and amplitude.

Diodes also announced four clock
buffers: the PI6CB18200,
PI6CB18401, PI6CB18601, and PI6CB18801.  The PCIe
4.0 2/4/6/8 HCSL output clock buffers are fanned-out from a reference input,
the company said, adding that like the clock generators, the slew rate and
amplitude of each output is programmable and there are individual output enables
for better power management. Additive jitter for the clock buffers is less than
0.05 ps.

Prices for the PI3DBS16212,
PI3DBS16412 signal switches range from $0.68 to $1.32. Prices for the
PI6CG18201, PI6CG18401, PI6CG18801, PI6CG15401 PCIe 4.0 clock generators and
PI6CB18200, PI6CB18401, PI6CB18601, and PI6CB18801 PCIe 4.0 clock buffers range
from $1.45 to $2.24 each in quantities of 5,000.