MAX2871 setting inquiry

Question

Dears. 
 We are considering the following: 1. REF_IN None external. 2. Is it possible to output RF OUTA at 250Mhz using only internal VCO? 3. Does REF_IN require external input? 4. I would like to output using only the internal VCO. Is it possible? 5. Can RFOUT be used as a single end? 
 Thank you

Heke · Accepted Answer

Hi ADL5350 , 
 You can output the VCO without having the REF in. In that case you need to control the VCO frequency by a voltage at TUNE input. The frequency won't be stable, thus do not assume exact 250MHz without an active feedback loop (e.e a PLL). 
 Probably you can use only one leg of the differential output. Ensure AC-coupling and equal loading to the unused leg, or use a balun or some diff-to-single i/f circuit. 
 Are you looking for a solution to provide 250Mhz stable clock? 
 Cheers, heke)

Heke · Answer

Hi ADL5350 , 
 The GUI is for configuring the registers of the synthesizer, thus you cannot set the VTUNE, as it is not directly controlled from the registers. You will need to provide the tuning voltage externally. Note: The VCO sensitivity is 100MHz/V, thus if your tuning voltage shifts 10mV, the output frequency shifts 1MHz. Supply voltage, load and temperature variations also modulate the output frequency, thus do not assume accurate and stable result in open loop operation. 
 It is not possible to offer any recommendation without knowing your specification and application. Is the 250MHz signal used for clocking a digital system or as a local signal for RF up/down-converter? Why you cannot use the reference clock input? What is the jitter and accuracy specification? 
 If you are looking for a solution that is not using external reference, try googling "CY2XF24" for an example. The output frequency can be set via I2C bus. Would that work for you? 
 Cheers, heke

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MAX2871 setting inquiry