Added Rf Synthesizer Frequency Accuracy Section; Added Example Frequency Accuracy Calculation Section - Analog Devices ADRV9005 Reference Manual

Reference Manual
SYNTHESIZER CONFIGURATION AND LO OPERATION
Figure 98. LO Switching Network (Receiver Channels Configured as Observation Receivers for Transmitter Channels)
Note that depending on the application, select the best phase noise or best-power saving options for better optimization.This changes the
frequency the internal VCO operates at to optimize for phase noise or power consumption. The option of best phase noise only works
for LO frequency under 1 GHz. The RF LO power consumption has three configurable options (Low, Medium High), which balance the power
consumption and RF LO phase noise. This option changes some of the analog DC biases to reduce the VCO voltage swing, and thus the
power consumption. High power means low LO phase noise, and vice versa.
The ADRV9001 provides two modes of retuning the PLL: the normal mode and fast mode. In terms of phase noise performance, there is
no difference between the fast and normal modes. However, the normal mode tracks temperature over time while the fast mode does not.
Therefore, the fast mode takes less time to complete retuning.
RF Synthesizer Frequency Accuracy
Although configuration of the RF synthesizer is valid to 1 Hz accuracy, the frequency might vary slightly. The actual carrier frequency can be
calculated from this based on the equation as follows:
Rf_synth_freq = round(f_carrier/f_step,max) × f_step,max
The frequency step size of the RF PLLs is given by the following equation:
f_step,max = DEV_CLK/((2^23−15) × RfLogenDivider)
where RfLogenDivider can be retrieved from the adi_adrv9001_Radio_RfLogenDivider_Get() API. The RfLogenDivider is based on the VCO
frequency and the LO optimization (power consumption/phase noise).
Example Frequency Accuracy Calculation
The desired carrier frequency is 4 GHz and the device clock is 307.2 MHz. LO optimization is set to 'Best Power Saving'.
From the adi_adrv9001_Radio_RfLogenDivider_Get() API, the RfLogenDivider was found to be 2.
The maximum frequency step can then be calculated as: 307.2 MHz/((2^23−15) × 2) = 18.31057962 Hz.
The actual carrier frequency can then be calculated as: round(4 GHz/18.31..Hz) × 18.31...Hz = 4.000 000 006 GHz i.e. 6 Hz offset from the
desired carrier frequency.
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Figure 97. LO Switching Network
ADRV9001
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