LTC6948IUFD-1

Clock Generators, PLLs, Frequency Synthesizers Overview

The LTC6948IUFD-1 is a fractional-N phase-locked loop (PLL) synthesizer featuring an integrated voltage-controlled oscillator (VCO). It operates within a VCO frequency range of 2.24 GHz to 3.74 GHz, supporting output frequencies from 0.373 GHz to 3.74 GHz via an internal divider. The device incorporates a reference divider, phase-frequency detector, ultralow noise charge pump, and a fourth-order delta-sigma modulator for spurious-free operation. Key electrical parameters include a maximum reference input frequency of 425 MHz, a programmable output divider ranging from 1 to 6, and supply voltages of 3.15 V to 3.45 V for digital/RF sections and 4.75 V to 5.25 V for the VCO and charge pump. It is housed in a 28-lead QFN package.

Clock Generators, PLLs, Frequency Synthesizers Feature Summary

• Ultralow Noise Performance: Achieves –226 dBc/Hz normalized in-band phase noise floor and –274 dBc/Hz normalized 1/f noise.
• Integrated VCO with Wide Range: Covers 2.24 GHz to 3.74 GHz internally, extendable to 0.373 GHz–3.74 GHz with output dividers.
• Advanced Modulator: Utilizes a 4th-order delta-sigma modulator to eliminate discrete spurious tones, enabling wide loop bandwidths.
• Programmable Architecture: Features an 18-bit fractional denominator, 8-step charge pump current settings, and SPI control interface.

Clock Generators, PLLs, Frequency Synthesizers Applications

• Wireless Basestations (LTE, WiMAX, W-CDMA, PCS)
• Microwave Data Links
• Military and Secure Radio Systems
• Test and Measurement Equipment

Clock Generators, PLLs, Frequency Synthesizers Procurement Notes

Verify the specific suffix '#PBF' indicates lead-free packaging compliant with RoHS standards. Confirm the 'I' temperature grade corresponds to the required operating junction range of –40°C to 105°C. Ensure the ordering part number matches the exact frequency band variant (LTC6948-1) required for the design, as other variants cover different VCO ranges.

Clock Generators, PLLs, Frequency Synthesizers Selection Notes

Select the LTC6948IUFD-1 when the target application requires a VCO frequency range between 2.24 GHz and 3.74 GHz. This variant is distinct from the -2, -3, and -4 models which cover higher frequency bands. Consider the output divider setting (O_DIV) to determine the final available output frequency range, noting that O_DIV=1 provides the full 2.24 GHz to 3.74 GHz span.

Clock Generators, PLLs, Frequency Synthesizers Part Context

The LTC6948 series comprises four variants differentiated by their integrated VCO frequency ranges. The LTC6948IUFD-1 specifically targets the lower end of the series spectrum (2.24 GHz to 3.74 GHz), while subsequent models (-2, -3, -4) address progressively higher frequency bands up to 6.39 GHz. All variants share identical pinouts, control interfaces, and core architectural features.

Clock Generators, PLLs, Frequency Synthesizers Replacement Considerations

Direct functional replacements within the same family include LTC6948IUFD-2#PBF, LTC6948IUFD-3#PBF, and LTC6948IUFD-4#PBF, provided the system can accommodate their respective higher VCO frequency ranges. No cross-family substitutes are documented in the official specifications.

Clock Generators, PLLs, Frequency Synthesizers FAQ

What is the maximum reference input frequency supported by the LTC6948?

The LTC6948 supports a maximum reference input frequency of 425 MHz.

How does the LTC6948 handle fractional spurs?

It employs an advanced 4th-order delta-sigma modulator in the fractional feedback divider, which converts quantization noise into high-pass shaped phase noise that is filtered by the loop, resulting in exceptionally low spurious levels.

What is the purpose of the MUTE pin?

The MUTE pin is an active-low CMOS input that mutes the RF differential outputs (RF+, RF–) while maintaining internal bias levels, allowing for quick response upon deassertion.