Today, signal-processing requirements in high-performance applications such as wireless base-station, instrumentation and broadband infrastructure, are stringent. Consequently, signal processing schemes are reaching astounding speeds, and jitter or the uncertainty of the clock edge can cause transmission errors and can have an adverse effect on a system's overall performance. To meet the extremely clean system clock needs of these applications, Analog Devices Inc. has developed a a new family of clock ICs that feature ultra-low jitter performance (sub picosecond) for significant noise reduction in system-critical signal chains.

In addition to low jitter, ADI's clock ICs improve system performance through the integration of several key functions that eliminate the need for multiple discrete components, reduce board space, and ultimately reduce bill-of-materials (BOM) costs. These features include a low-phase-noise, phase-locked loop (PLL) frequency synthesizer core, programmable dividers, and adjustable delay blocks. Combined with sub-picosecond jitter performance, these features result inthese clock ICs maximizing the performance of critical-signal-path components, such as analog-to-digital converters (ADCs), digital-to-analog converters (DACs), direct digital synthesizers (DDSs) and mixed-signal front end (MxFE) devices.

ADI's clock distribution IC series includes the AD9510, AD9511 and AD9512. These devices feature sub-picosecond performance over a broad frequency range, higher levels of integration and more programmability than other solutions. These clock distribution ICs feature LVPECL outputs, as well as user-selectable LVDS and CMOS options:

• LVPECL outputs operate to 800 MHz with additive jitter less than 250 fs (femtoseconds) rms.
• LVDS and CMOS outputs operate up to 800 MHz and 250 MHz, respectively.
• In both LVDS and CMOS modes, the additive jitter is less than 300 fs (rms).

The voltage levels for both LVPECL and LVDS clock outputs are programmable, allowing the system designer to determine the best voltage swing for a given application. The AD9510 offers the most flexibility, mixing LVPECL, LVDS and CMOS logic for a total of eight independent clock outputs. For designs requiring fewer outputs, the AD9511 and AD9512 pack five independent outputs into a smaller package at reduced power consumption.

By using dividers with increased functionality, the clock distribution ICs eliminate the extra components required to generate gate delays and phase shifts. In addition, each clock divider is programmable to any integer ratio from one to 32, offering flexibility when handling multiple frequencies on a single printed circuit board (PCB). The divide function also includes a user-selectable offset word that enables channel-to-channel phase control. Because the devices perform phase control inside the divider block, they maintain much lower jitter than equivalent discrete implementations. Also, the clock distribution ICs feature on-chip programmable delay allowing users to adjust for set-up and hold-time requirements between data converters and digital ASICs, FPGAs, and digital up/downconverters, without adding extra clock hardware. All three AD951x products include at least one fine-delay-adjust channel with a programmable full-scale range from 1 ns to 10 ns. A 6-bit delay word offers 64 unique delay settings with step sizes as low as 16 ps.

Both the AD9510 and the AD9511 integrate a low-phase-noise, 1.5 GHz PLL frequency synthesizer core on chip. The PLL is optimized for clock applications and consists of a programmable reference divider, a low-noise phase frequency detector, a precision charge pump, and a programmable feedback divider. For applications that do not require an on-chip PLL, the AD9512 offers two 1.5 GHz clock inputs and five independent clock outputs.

While the AD9510 is sampling now, production quantities are slated for February 2005. Likewise, AD9511 and AD9512 will begin sampling this month, with production quantities to be available in March next year. The AD9510 is offered in 64-lead LFCSP (lead frame chip scale package) and is priced at $11.95 per unit in 1,000-piece quantities. All three AD951x products are specified to operate over the extended industrial range of -40°C to +85°C.

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