ADF4251

Obsolete

Lowest Phase Noise PLL Synthesizer using Fractional-N Technology

Data Sheet (Rev. 0) Product Selection Table

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Overview

Sigma-delta based fractional-N technology ensures superior
Phase Noise and spurious performance is maintained over temperature
Hardware and Software Power-Down
Flexibility of programmable fractional-modulus ensures exact output frequencies can be synthesized.
0.1 - 3.0GHz Fractional-N / 0.05 - 1.2GHz Integer-N PLL's
3 wire Serial Interface with 1.8V logic compatibility
250MHz REF_IN Frequency
8 x Programmable charge pump currents
PFD frequencies up to 30MHz allow faster settling and lower phase noise.
Supported on ADIsimPLL software design tool
Available in 4x4mm Chipscale package
2.7 - 3.3V Power Supply with separate V_P to 5V

The ADF4251 Fractional-N Synthesizer when combined with a VCO and loop filter forms a complete phased locked loop (PLL). This solution from ADI creates state-of-the-art LO's (local oscillator) for the upconversion and downconversion of RF signals in Wireless applications. The ADF4251 can provide the LO for both RF and IF sections. The RF section incorporates Fractional-N techniques while the IF section uses integer-N techniques. The ADF4251 PLL consists of a low noise digital phase frequency detector (PFD), a precision charge pump, a programmable reference divider, programmable integer registers. Programmable modulus fractional interpolator.

-103dBc/Hz In-band Phase Noise performance for GSM 1800MHz conditions (as an example) is approximately a 15dB improvement over the ADI best Integer-N PLL Phase Noise (ADF4106) and a 10dB improvement over competing F-N PLL products available today. Fractionality will provide for higher PFD reference which will allow wider loop bandwidth for fast lock times. This product is targeted principally at Handset and infrastructure applications requiring low phase noise, fast settling, small channel steps at high output frequencies.

Evaluation board with software is available. There is also a full data sheet with performance graphs. Additionally, the device is featured on ADIsimPLL Synthesizer simulation tool.