News and New Products

FROM EDN EUROPE: Synthesiser chip challenges HF-crystal oscillators

by Graham Prophet -- EDN Europe, 10/13/2005

In its mixed-signal chips, Silicon Laboratories employs a frequency-synthesis technique for clock generation that it calls DSPLL: now, it is launching a range of frequency-source parts that embody that technology to perform the same function as standard crystal oscillators and voltage-controlled crystal oscillators. The Si 5390 and 550 are frequency-synthesis chips that the company will pre-programme to produce up to four output frequencies (selectable) from a base frequency that a low-cost, standard, fundamental crystal generates.

Silicon Labs has created the product to exactly match today's market for XOs and VCXOs; if you have a need for a high-stability source of a specific frequency, you can place an order with a crystal oscillator manufacturer, and in due time they cut the required crystal element and ship your oscillator. The 530/500 parts aim to mimic that process but on top of that cut delivery time to days, and improve on most of the existing oscillator specifications such as stability and reliability. The chip employs DSP techniques together with a very-low-jitter voltage-controlled oscillator. The chip produces VCO operation digitally rather than by "pulling", yielding better stability and much-improved linearity (better than ±1%). Also contributing is internal regulation of the supply voltage rails. Operation is up to from 10 MHz to 1.4 GHz (square wave, 50% duty-cycle output) with jitter of under 0.3 psec rms, and the resolution-according to Silicon Labs' Director Mike Petrowski-is in excess of 40 bits, or under 1 part-per-billion.

If frequency is fully selectable digitally, why not give the user control of that frequency-selection process? Petrowski noted that the company has tailored this part to match the existing market model for XO supply and declined to comment on where such a user-settable chip might appear in the future. Likewise, he acknowledged that there is no impediment to extending the technique to other environments where designers need crystal stability in frequency sources, such as oven-stabilised circuits. Depending on features selected, the chips-which are delivered as a single package containing IC and reference crystal-sell for $6.05 to $88.95 (1000).

Silicon Labs, www.silabs.com