MAX2871 setting inquiry

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

Dear. HEKE

How much should I input into the Tune Input?
How should I configure the loop filter?
If you have a better solution, please suggest it.
Thank you for your support.

DEAR.HEKE

I would like to set it up in the GUI of MAX2871 as follows.
When REF_FREQ is '0' in the GUI, a red warning is received.

How can I set it to the following conditions?
Disable the REF_REFQ (REFIN) input.
I want to output using only internal VCO.
RF_OUTA, OUTB is 250Mhz.

Is it possible to set TUNE INPUT in GUI?

Setting REF_FREQ to '0' changes both OutA and B to 0.

Thank you

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

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

Dear HEKE

Thank you for your support.

LO signal for RF Up/Down-converter.

Let's review the external clock input.