The LMX2487E is a low power, high performance delta-sigma fractional-N PLL with an auxiliary integer-N PLL. It is fabricated using National Semiconductor's advanced process. With delta-sigma architecture, fractional spurs at lower offset frequencies are pushed to higher frequencies outside the loop bandwidth. The ability to push close in spur and phase noise energy to higher frequencies is a direct function of the modulator order. Unlike analog compensation, the digital feedback technique used in the LMX2487E is highly resistant to changes in temperature and variations in wafer processing. The LMX2487E delta-sigma modulator is programmable up to fourth order, which allows the designer to select the optimum modulator order to fit the phase noise, spur, and lock time requirements of the system. Serial data for programming the LMX2487E is transferred via a three line high speed (20 MHz) MICROWIRE interface. The LMX2487E offers fine frequency resolution, low spurs, fast programming speed, and a single word write to change the frequency. This makes it ideal for direct digital modulation applications, where the N counter is directly modulated with information. The LMX2487E is available in a 24 lead 4.0 X 4.0 X 0.8 mm LLP package.
The LMX2487E is a low‑power, high‑performance delta‑sigma fractional‑N PLL with an auxiliary integer‑N PLL, fabricated using National Semiconductor’s advanced process. It features a programmable up‑to‑fourth‑order delta‑sigma modulator, fine frequency resolution, fast programming via a three‑line 20 MHz MICROWIRE interface, and is offered in a 24‑lead 4.0 × 4.0 × 0.8 mm LLP package.
The document provides a functional block diagram, pin descriptions, absolute maximum ratings, recommended operating conditions, electrical characteristics, RF and IF synthesizer parameters, phase‑noise data, and typical performance curves. It also includes mechanical dimensions, package ordering information, and legal notices.
| Package | 24‑lead 4.0 × 4.0 × 0.8 mm LLP |
|---|---|
| RF PLL Frequency Range | 3.0 GHz to 7.5 GHz |
| Power Supply Voltage | 2.5 V to 3.6 V |
| Operating Temperature | -40 °C to +85 °C |
| Input Sensitivity (RF PLL) | 3‑6 GHz, 6 dBm |
| Phase Noise (RF_CPG =0) | -202 dBc/Hz |
It is supplied in a 24‑lead 4.0 × 4.0 × 0.8 mm LLP package.
The device operates from –40 °C up to +85 °C.
Serial data is transferred via a three‑line high‑speed (20 MHz) MICROWIRE interface.
The RF PLL can synthesize frequencies from 3.0 GHz to 7.5 GHz.