Time was when high-speed clock generation was about supplying clock signals to CPUs. But with the proliferation of graphics hardware, high-speed I/O, and RF in everything from handsets to server farms, the CPU has ceased to be the only important market for fast clock generators. If fact the whole PC industry may be in the shadow of networking, enterprise computing, and consumer electronics in this regard.

But these broader markets have their own needs in addition to the obvious cost and power constraints. These applications need a vast array of different frequencies, differing degrees of jitter control, and in some cases frequency-spreading and other interesting features. In recent days both Cypress Semiconductor, one of the pioneers in programmable clock generators, and Cypress spin-off SpectraLinear have introduced new families of clock chips. The two have started with similar circuitry but taken two remarkably different approaches to these diverse markets.

This may come of something of a surprise to Cypress, which thought that it was spinning off a specialized group focusing on clocks for PC motherboards. But SpectraLinear has been quietly expanding beyond this corner of the market for quite a while, and now lists many of the same applications as Cypress in its market focus. Differences in detailed specs may make the two new families complementary in many cases, but the two vendors are definitely beginning to overlap.

One point the two new lines—FleXO from Cypress and Ready Clock from SpectraLinear—have in common is that internally they are programmable PLL-based clock generators, not fixed-frequency oscillators. This becomes hugely important when you look at the range of frequencies that can come up in modern designs. As Cypress business-unit director Sudhir Gopalswami pointed out, there are basically two alternatives to precise clock generation out there: SAW oscillators or overtone crystal oscillators. Both are expensive and have to be built for a specific frequency. Just getting a non-standard crystal to drive them can be expensive and time-consuming.

Both Cypress and SpectraLinear have taken this concept to market, but in different ways. Cypress provides several configurations of one basic chip—as a synthesizer or VCO with external-crystal inputs, or packaged with a crystal in a standard ceramic pack as a crystal oscillator or a crystal-controlled VCO. Either the company will program the part to your specifications or they will simply sell you their programmer. SpectraLinear, in contrast, is offering their part as a huge array of standard products: 41 at announcement, to be exact, with the ability for customers to define their own on the fly. In effect, you buy the frequency you need off the shelf. Inside, the parts are programmable, but you don't have to worry about that—you buy the chip as if it were a fixed-frequency oscillator.

The two lines have different specs and features as well. FleXO spans the entire frequency range from 50 MHz to 690 MHz with one chip, with a very tight 0.6 ps RMS jitter spec across the full useful range of the part. There is a cost for this precision, however, as any analog designer can tell you: power. The FleXO chips consume from 90 to 140 mA, depending upon the way they are programmed, Gopalswami said. The loading was not stated.

One interesting additional feature available in the parts that are packaged with the crystal is what Cypress calls frequency margining: the ability to move off-frequency in 0.2 ppm increments in either direction, under control of the chip's i²C interface. This has obvious uses in manufacturing test and troubleshooting.

SpectraLinear's 41 chips cover a range of preset frequencies from 12.000 to 150.000 MHz with various options. Eventually the parts will span from 1 MHz to 200 MHz output, and will use standard crystals at 24, 25, 27, or 48 MHz. Because the chips are standard products, you don't program them. You order a chip using the GUI on the company Web site, and SpectraLinear ships within 1 day. In Q4, the company will upgrade this to same-day shipping. With your chips you get a full data sheet characterizing the part with the options you have requested. This way there are no surprise consequences for a particular programming configuration, commented director of marketing Cavit Ozdalga. If you don't find the frequency and features you want on the standard-product list, you can configure-your-own on the Web site, and SpectraLinear will program it up for you.

The frequency range is lower on the Ready Chip parts, and the jitter spec—at less than 100 ps, measured at 50 MHz, 3.3 V into a 15 pF load, is considerably relaxed compared to the precision FleXO. But in exchange you may save power: the Ready Chip draws only 5 mA at 3.3 V and 0 load capacitance.

In the features department, the Ready Chip does not have frequency margining, but it does have configurable spreading: selectable as disabled, ±0.25 percent, or ±0.75 percent, based on a SpectraLinear profile. The chips are available only in a lead-free 4.4 mm 8TSSOP, not in a crystal package. Pricing on the Ready Chip is less than a dollar in 1K quantities.