In this regard, SiTime points out a difference between its oscillators and earlier programmable quartz oscillators that used ring oscillator PLLs that produced jittery outputs. The company’s Sigma-Delta Fractional-N LC PLL is different. SiTime says it reduces clock jitter to levels comparable with or better than fixed-frequency oscillators.
Interestingly, because the MEMS resonators are thinner than any packaged quartz crystal, they allow SiTime to package particularly thin oscillators—down to 0.25 mm. Standard footprints are 2.5 by 2.0, 3.2 by 2.5, 5.0 by 3.2, and 7.0 by 5.0 mm. But the very low height profile compared to crystal oscillators makes them particularly appealing in mobile products.
Product families are differentiated by application area. In the high-performance family, with output frequencies up to 800 MHz, integrated phase jitter is less than 1 ps and rms jitter is less than 3 ps. Low-power oscillators, programmable to any frequency between 1 and 110 MHz, draw under 3.5 mA from 1.8 to 3.3 V and start up in 3 ms. Another line offers programmable spread-spectrum dithering, and a line of multi-output oscillators in single packages is intended for systems that require multiple clock frequencies.
SpectraLinear’s programmable EProClock spread-spectrum clock generators are partly a product-cost sell. The company says they provide the same performance as high-performance crystal oscillators, SAW oscillators, or voltage-controlled oscillators, but cost significantly less.
Yet even more, the story is about faster development time and short ordering leadtime. SpectraLinear says they provide considerable on-the bench flexibility with an extensive library of multiplexers and programmable elements. Available within hours or days of product definition, the company says, each product has more than 2000 control points.
The parts promise to cut out delays associated with ordering customized parts by making it possible to optimize any device for its intended application by programming operating speed, spectral phase noise, timing jitter, power, heat, and radiated emissions. This includes programming output frequencies from 3 to 200 MHz using either crystal or clock input. By programming drive levels, designs can accommodate seven different rise and fall times.
For spread-spectrum, it is possible to individually program frequency (25 to 120 kHz), spread (0.25% to 5.0%, center or down), and profile, (Lexmark or Triangular). These can be programmed in-circuit, which helps minimize test time while ensuring that products meet Part 15 standards. Similarly, designers can vary clock output drive strength and adjust rise and fall times on the bench to perform noise sensitivity analysis.
Also, there are seven independent programmable output drive-strength levels for each output. Jitter performance can be traded off for power dissipation. Single-PLL generators may have up to four clock outputs. Four-PLL generators may have up to 12. On-chip crystal-load capacitors eliminate the need for external crystal load capacitors.
Zarlink’s novel is to approach is to shrink the solution size by squeezing everything needed for clock generation onto a single chip. The company notes that traditionally, a large number of clock oscillators, crystals, and fixed-frequency clock generator and multiplier ICs have been required to satisfy the diverse clocking requirements of CPU, memory, DSPs, framers, physical layers, and other components.
Yet Zarlink notes that new single-chip silicon clock generation products can effectively manage and control dataflow across multiple components for a range of applications. Beyond board space advantages, the company says, these single-chip solutions reduce power consumption, ease system validation, simplify frequency margining, and help improve overall reliability. Most importantly, Zarlink claims, their unique architecture supports any rate to any rate frequency translation, where traditional M/N and fractional-N multiplication have frequency and performance limitations.
Zarlink’s ClockCenter platform for high-speed optical transport network (OTN) and communications equipment comprise multichannel synchronous clock translators and free-run clock generators. They provide “any-rate to any-rate frequency translation,” according to the company. Specifically, ClockCenter synchronous products accept and generate any frequency (1 kHz to 720 MHz). ClockCenter free-run products were developed to allow designers to replace multiple oscillators, logic converters, and fan outs to time processors, memory chips, physical-layer (PHY) chips, and other components with an integrated single-chip device.