Fanout Buffers, Dividers, and Multiplexers


The IDT clock buffer (fanout buffer), clock divider and clock multiplexer portfolio includes devices with up to 27 outputs. Differential outputs such as LVPECL, LVDS, HCSL, CML, HSTL, as well as selectable outputs, are supported for output frequencies up to 3.2 GHz and single-ended LVCMOS outputs for frequencies up to 350 MHz. Some buffers are available with mixed output signaling. IDT’s buffer portfolio has devices supporting supply voltages from 1.2 V up to 5 V and that are available in commercial and industrial temperature ranges. Fanout buffers and clock dividers are general-purpose clock building block devices that can be used in any number of applications. They are ideal for clock and signal distribution in a large variety of systems, from personal computers to consumer electronics or industrial systems, as well as high-performance networking and communications systems.

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Fanout Buffers

Fanout buffers are a useful building block of many clock trees, providing signal buffering and multiple low-skew copies of the input signal. The clock buffer from a single input reduces loading on the preceding driver and provides an efficient clock distribution network. Single output clock buffers are useful for translating a clock from one signaling standard to another (e.g. LVCMOS-in to LVPECL-out). Some devices have an integrated crystal oscillator, requiring only a low cost external fundamental-mode quartz crystal. The integrated oscillator provides an extremely low phase noise reference clock to drive jitter-sensitive devices such as the clock inputs of PHYs. If the exact buffer configuration is not found in the extensive IDT fanout buffer offerings, customers may consider devices in the IDT clock divider or clock multiplexer portfolio that, when used in divide-by-1 mode or proper select mode, can also function as a fanout buffer.

Clock Dividers

Clock dividers provide an output clock signal that is a divided frequency of the input. They can also be used as clock buffers and make multiple copies of the output frequency. Clock divider devices, when used in divide-by-1 mode, can also function as a fanout buffer.

IDT’s “8” series of fanout buffers and clock dividers feature fully differential internal architecture, even devices with single-ended I/Os. This improves jitter due to inherent common-mode noise rejection and improves output skew. The differential circuitry is constant-current and therefore injects less noise into system power supplies than single-ended solutions, reducing EMI compliance concerns.

Clock Multiplexers

A clock multiplexer selects one of the several inputs and propagates that signal forward. IDT offers several types of clock multiplexers that not only include a multiplexing function, but also clock divider and fanout buffer functions integrated on the same device. This not only reduces the total part count in a clock tree, but can also help improve the performance in many cases.