SNAS736C June 2017 – April 2019 LMX2595
The LMX2595 is a high-performance, wideband frequency synthesizer with integrated VCO and output divider. The VCO operates from 7.5 GHz to 15 GHz, and this can be combined with the output divider to produce any frequency in the range of 10 MHz to 15 GHz. The LMX2595 also features a VCO doubler that can be used to produce frequencies up to 20 GHz. Within the input path, there are two dividers and a multiplier for flexible frequency planning. The multiplier also allows the reduction of spurs by moving the frequencies away from the integer boundary.
The PLL is fractional-N PLL with a programmable delta-sigma modulator up to 4th order. The fractional denominator is a programmable 32-bit long, which can easily provide fine frequency steps below 1-Hz resolution, or be used to do exact fractions like 1/3, 7/1000, and many others. The phase frequency detector goes up to 300 MHz in fractional mode or 400 MHz in integer mode, although minimum N-divider values must also be taken into account.
For applications where deterministic or adjustable phase is desired, the SYNC pin can be used to get the phase relationship between the OSCin and RFout pins deterministic. When this is done, the phase can be adjusted in very fine steps of the VCO period divided by the fractional denominator.
The ultra-fast VCO calibration is designed for applications where the frequency must be swept or abruptly changed. The frequency can be manually programmed, or the device can be set up to do ramps and chirps.
The JESD204B support includes using the RFoutB output to create a differential SYSREF output that can be either a single pulse or a series of pulses that occur at a programmable distance away from the rising edges of the output signal.
The LMX2595 device requires only a single 3.3-V power supply. The internal power supplies are provided by integrated LDOs, eliminating the need for high-performance external LDOs.
The digital logic for the SPI interface and is compatible with voltage levels from 1.8 V to 3.3 V.
Table 1 shows the range of several of the dividers, multipliers, and fractional settings.
|OSCin doubler||0 (1X)||1 (2X)||The low noise doubler can be used to increase the phase detector frequency to improve phase noise and avoid spurs. This is in reference to the OSC_2X bit.|
|Pre-R divider||1 (bypass)||128||Only use the Pre-R divider if the multiplier is used and the input frequency is too high for the multiplier.|
|Multiplier||3||7||This is in reference to the MULT word.|
|Post-R divider||1 (bypass)||255||The maximum input frequency for the Post-R divider is 250 MHz. Use the Pre-R divider if necessary.|
|N divider||≥ 28||524287||The minimum divide depends on modulator order and VCO frequency. See N-Divider and Fractional Circuitry for more details.|
|Fractional numerator/ denominator||1 (Integer mode)||232 – 1 = 4294967295||The fractional denominator is programmable and can assume any value between 1 and 232–1; it is not a fixed denominator.|
|Fractional order (MASH_ORDER)||0||4||Order 0 is integer mode and the order can be programmed|
|Channel divider||1 (bypass)||768||This is the series of several dividers. Also, be aware that above 10 GHz, the maximum allowable channel divider value is 6.|
|Output frequency||10 MHz||20 GHz||This is implied by the VCO frequency, channel divider, and VCO doubler.|