Max2870 no output signal

Hello.

The question provides very little detail other than you designed a PCB and there is no RF output.  It could be due to a defective PCB, PCB design error, firmware error or something else.  All I can provide are some general debugging guidelines.  I assume you have tested more than one of your PCBs and get the same result on multiple units so as to rule out a defective PCB (e.g. an open or short or assembly error such as missing 50 ohm pull-up resistor on the output or missing AC coupling cap etc.)  

If it was me, I would next compare the schematic of my PCB vs. the schematic of the breakout board assuming it is available, otherwise against the schematic of the MAX2870 EVKIT.  You can find the schematic in the EVKIT datasheet.  I would do a thorough comparison going around every pin of the MAX2870 and paying close attention to the circuitry on the RF outputs.  Investigate any differences between PCB schematics to rule them out as a possible cause.  Next I would use a DMM to check as much of the PCB as I can to confirm I get expected readings.  For example, are the VCC pins getting the correct voltage.  Is every VCC pin connected to the supply?  Is every single GND pin on the IC connected to ground?

If the PCB schematic checks out, next look into your firmware as a possible cause.  The IC datasheet warns the reader not to assume that registers will power up with default settings.  One should always program the registers after power-up, even if one doesn't need to change the default settings.  So confirm you are doing that.  The IC datasheet provides a detailed "clean start up"  sequence after power on, on page 13.  The registers should be programmed in a specific sequence.  I would make sure your firmware follows the sequence exactly as written.  In the IC datasheet, they provide the contents of all registers for each of the Typical Operating Characteristics plots.  Perhaps try programming the registers with the same settings used for the 3GHz closed loop phase noise vs frequency plot.

Hope it helps.

Best Regards

Andrew

Thank you Andrew. 

You have provided a complete review. 

Actually I have designed the PCB in compliance with the reference design and have done these tests. I have completed the firmware development before designing the PCB and tested it well on the breakout board. 

But my question is what is the reason for not having signal on the outputs even though the lock is done and the LED is shining and turns off when I disable RFOEN so it seems to be working fine. 

I have a question I hope you can answer that might be the cause of the problem. I am using a single ended structure for both outputs and I connected the unused output with a 50 ohm load to ground. In this case, can it work without the pull-up resistors on the terminated output or should I keep them?

Thanks in advance

Hello,

OK I will trust your firmware is not the cause of the problem since it sounds like you have tested it thoroughly on the breakout board.   I am not clear what this LED you refer to is.  Is the LD output of the IC driving an LED on your PCB to indicate PLL lock?  I would not expect the lock state of the PLL to depend on whether or not either of the RFOUT outputs are enabled.  Disabling an RFOUT has nothing to do with the PLL so that observation is odd.  

As for your question about termination, I think there is no reason to terminate the unused output to ground.  Both P and N outputs should have 50 ohm pull up resistors to VCC even though you only use one of them.  This may well be the cause of the problem.  It is simple enough to do an experiment to confirm by just removing the 50 ohm pulldown termination and putting in a 50 ohm pull-up.

BR

Andrew

Hello,

OK I will trust your firmware is not the cause of the problem since it sounds like you have tested it thoroughly on the breakout board.   I am not clear what this LED you refer to is.  Is the LD output of the IC driving an LED on your PCB to indicate PLL lock?  I would not expect the lock state of the PLL to depend on whether or not either of the RFOUT outputs are enabled.  Disabling an RFOUT has nothing to do with the PLL so that observation is odd.  

As for your question about termination, I think there is no reason to terminate the unused output to ground.  Both P and N outputs should have 50 ohm pull up resistors to VCC even though you only use one of them.  This may well be the cause of the problem.  It is simple enough to do an experiment to confirm by just removing the 50 ohm pulldown termination and putting in a 50 ohm pull-up.

BR

Andrew