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Extending ADF4193 Vtune range

Learn how to extend the Vtune range of the ADF4193 by bypassing the internal differential amplifier stage and implementing an external quad-stage op-amp with variable CMR voltage. Explore different methods and their impacts on settling time and phase noise.

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Extending ADF4193 Vtune range

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  1. Extending ADF4193 Vtune range Austin Harney

  2. ADF4193 standard application circuit

  3. 1. ADF4193 Extend Vtune range by bypassing internal diff amp stage and implement this using external quad stage op-amp and variable CMR voltage (e.g. OP484) Gain of Diff amp = R2d/R1d SW3 switch controlled using Muxout = SW3 Timeout Signal Powerdown internal diff amp in Register5

  4. 1. ADF4193 Extend Vtune range using OP484 ADF4193 charge pump output swing = 4V (1.2V to 5.2V), so if set gain of diff amp = 1, need to use adjustable CMR to set the centre of the tuning range. To cover a Vtune of 2V to 14V for example would need programmable CMR values of 4V, 8V, 12V. This would allow you to cover 2V to 14V. The CMR voltage needs to be set quickly enough to not impact settling time during hopping. Alternative is to use gain in diff amp, e.g. with R2d = 1k and R1d = 500r and using CMR voltage = 5V would achieve a tuning range from 1V to 9V

  5. 2. ADF4193 Extend Vtune using external non-inverting op-amp. Simple approach but phase noise gets gained up by op-amp gain This only gains up charge pump output voltage so 1.2V to 5.2V output range would become 2.4V to 10.4V with gain=2, not suitable if lower Vtune required

  6. 3. ADF4150HV to directly drive extended range VCO. PLL LBW = 1MHz to achieve us locktimes. Depending on spurious requirement this might be simplest solution

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