ADRF6755 RF output

Hi, 

After setting the attenuation value to 0 dBm, I am getting -24dBm for 1GHz.I have attached schema and other details. If any suggestion you have, let me know.

1)REFF input CLK And PFD set -40Mhz (/2,bubbler&5bit Rdivider all are disabled.)

2)output frequency range-950Mhz to 2150Mhz

3)loop filter values same as ADRF EVM 

4)Register CR9[7:4] = 0xF (5mA cp output current setted)

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  • +2
    •  Analog Employees 
    on Nov 25, 2020 3:03 PM 4 months ago

    Hello,

    If you get a lower output power than expected but it is at the right frequency on PLL VCO integrated IQMOD,  first, check if baseband inputs are at the right condition. The condition is specified at the SPECIFICATION section and TPC section in the datasheet. Baseband inputs(IBBP/IBBN/QBBP/QBBN) are at 0.9Vp_p differential @0.5V DC biased. Please check it with an oscilloscope at high-impedance. At this condition, it should be around 0dBm typical.

    For the schematic, No AC- Coupling capacitor on the Reference Input circuit. Make sure Reference Input AC-Coupled. Reference & PFD Frequency with the charge pump setting on the suggested loop filter is okay. Make sure the reference input signal level is 0.4~VREG(3.3V) range.

    Are 499 ohm on R227,R233,R251, R259  termination resistors for DAC?  and it looks 1.6Kohm R704, R247 are to interface to 1Kohm differential termination resistors. Please refer to the Baseband Inputs section for DAC and ADRF6755 baseband input interface.

    Thanks

    Tony

  • Hi Tony,

    Thanks a lot for your valuable comments. The Above mentioned points had checked. We connected the REFIN pin to Si5338 CMOS Ac coupled output. We find out Baseband input biasing level is different. Our DAC is a 12bit current steering  DAC, its Typical common-mode voltage and current 0.6V (max 0.7V) and 2mA(max 3mA)&AVDDHV=2.5V.So DC biasing voltage and differential voltage level are different. If you have any termination method, please suggest.

Reply
  • Hi Tony,

    Thanks a lot for your valuable comments. The Above mentioned points had checked. We connected the REFIN pin to Si5338 CMOS Ac coupled output. We find out Baseband input biasing level is different. Our DAC is a 12bit current steering  DAC, its Typical common-mode voltage and current 0.6V (max 0.7V) and 2mA(max 3mA)&AVDDHV=2.5V.So DC biasing voltage and differential voltage level are different. If you have any termination method, please suggest.

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