8-GHz PLL synthesizer IC streamlines converter stages

Norwood, Mass.—Eliminating the need for frequency multiplier stages, thereby slashing cost in RF designs, IC maker Analog Devices, Inc . (ADI), rolls out the industry's first 8-GHz PLL (phase-locked loop) synthesizer chip.

ADI's latest ADF4108 can be used in broadband wireless access, satellite communications, instrumentation, WLAN (wireless LANs), and base station designs. The ADF4108 device can be used to implement LO s (local oscillators) in up-conversion and down-conversion sections of receivers and transmitters.


Although there's no VCO (voltage controlled oscillator) aboard (yet), the IC comprises a low-noise digital PFD (phase frequency detector), a precision charge pump, a programmable reference divider, programmable A (6-bit) and B (13-bit) counters, and a dual-modulus prescaler (P/P+1 ).

The A and B counters, in conjunction with the dual-modulus prescaler, implement an N divider (N = BP+A ). In addition, the 14-bit reference counter (R counter) lets selectable REFIN (reference) frequencies at the chip's PFD input.

Click to view block diagram

The ADF4108 operates over a power supply range of 3.2-V to 3.6-V, and a separate charge pump supply pin (VP ) can support extended tuning voltage in 3.3-V systems. A complete PLL can be implemented if the synthesizer is used with an external loop filter and VCO.

Power Managed

The IC also offers hardware-programmable power-down modes, enabled by a CE (chip enable) pin. When the CE pin is low, the device is immediately disabled. You also get an asynchronous power-down mode. In a programmed synchronous power-down, the device power-down is gated by the charge pump to prevent unwanted frequency jumps.

Three-Wire Serial Control

The ADF4108 also uses an SPI -compatible (serial peripheral interface) port for writing to the device. The maximum serial clock rate is 20-MHz. This translates to a maximum update rate of 833-kHz, or one update every 1.2-µs, which is more than adequate for systems that have typical lock times in hundreds of microseconds.

Price And Availability

The ADF4108 is available now in a LFCSP (lead-frame chip-scale package), priced at $3.30 ea/1000.

Click here for a datasheet (in Adobe Acrobat .PDF format).

For more information, contact Analog Devices, Inc., 804 Woburn St., Wilmington, Mass. 01887. Phone: 800-ANALOGD (800-262-5643) or 781-937-1428. Fax: 781-937-1021.

Analog Devices , 800-262-5643,

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