Iq Fm/Fsk - Analog Devices ADRV9001 User Manual

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DPD
DPD is an optional feature available in the ADRV9001 device to enable users to achieve higher power amplifier efficiency while still meet
Error Vector Magnitude (EVM) and adjacent channel leakage ratio (ACLR) requirements in their Tx signal chain for compliance with
the standards requirements. DPD works on the principle of pre-distorting the Tx data to cancel distortion caused by power amplifier
compression. It utilizes the tracking calibration to capture the transmitted data samples and the data samples looped back through ORx
to estimate the distortion parameters. By applying the estimations in the real time, the transmitted signal is pre-distorted to compensate
for the power amplifier nonlinearity.
For more detailed information, please refer to the Digital Predistortion section in the User Guide.
TX NCO Internal Signal Source
The ADRV9001 has an internal quadrature NCO which serves several purposes. First, it could be used to generate the calibration tone
for the initial calibrations such as the Tx QEC. Second, it can be used to verify the functionality of the datapath. In both cases, as shown
in Figure 86, the Tx preprocessor takes the input data from NCO instead of data interface.
The NCO has a 32-bit phase accumulator. The NCO clock frequency for the phase accumulator is programmable. It is either set by the
profile to the interface rate or overwritten by the calibration task. To test the datapath, the user can generate a tone with a frequency
resolution of Fclk/232 up to Nyquist frequency through the API command "adi_adrv9001_Tx_NcoFrequency_Set()".
FM/FSK Modulation
The ADRV9001 provides a FM/FSK modulation for standards which use constant-envelope frequency modulation scheme, such as
DMR, Analog FM, P25 Phase 1 and Phase 2. It also provides an optional capability to perform symbol mapping and interpolation
operation on the Tx data received from baseband processor for FM/FSK modulation. This capability provides user more flexibility when
preparing Tx data for transmission. User has an option to send either pre mapped and interpolated Tx data by enabling this functionality
or send post mapped and interpolated data by bypassing this functionality in ADRV9001. For example, for the Digital Mobile Radio
(DMR) standard which uses 4.8ksps symbol data. baseband processor could send the symbol data directly to ADRV9001 and let
ADRV9001 map the symbol data and then interpolate the data to generate frequency deviation data. Note this functionality is currently
not enabled in the datapath and will be provided to user in the future.
Currently, to utilize the FM/FSK modulation capability of ADRV9001, user should perform symbol mapping, interpolating and pulse
shaping filtering in baseband processor to generate frequency deviation data before sending to ADRV9001. Two different options of
FM/FSK modulation are deployed in the ADRV9001 which are Direct FM/FSK and IQ FM/FSK as shown in Figure 86. They are briefly
discussed in the following subsections.
Direct FM/FSK
Frequency modulation is implemented by modulating the Tx RF PLL directly in Direct FM/FSK option. The Tx datapath with Direct
FM/FSK is shown in Figure 93.
FRAC–N
ANALOG
PLL (TX)
IN
ATTENUATOR
FM MOD.
As shown in Figure 93, the baseband processor TX_DATA can optionally go through the symbol mapping/interpolation and
programmable FIR, and after interpolation and frequency deviation mapping, the Frac-N PLL implements the FM/FSK modulation at
the desired RF output frequency. Finally, the PLL output is attenuated before feeding to the TX RF interface. The programmable 128-tap
FIR works as the pulse shaping filter in this scenario, customer could optionally load their filter coefficients according to the standard
requirement through API commands. Note this feature is currently not available but will be provided in future releases. In Direct
FM/FSK modulation, the DAC and LPF could both be powered down and some digital blocks such as the common interpolators, power
amplifier protection and Tx attenuation control could all be bypassed. Therefore, it could result in a significant power saving.

IQ FM/FSK

IQ FM/FSK modulation is implemented by modulating the digital NCO as shown in Figure 86. The modulated IQ data goes through
interpolator, DAC, LPF, and then be upconverted to RF frequency by mixer. The previous processing stages before the digital FM/FSK
modulator are similar to Direct FM/FSK option, which also contains optional symbol mapping/interpolation and pulse shaping
functions. The selection between direct FM/FSK and IQ FM/FSK is determined by profile.
FREQ_DEV NARROWBAND
MAPPER INTERPOLATORS
Figure 93. Direct FM/FSK Data Path Block Diagram
Rev. PrA | Page 96 of 253
Preliminary Technical Data
SYMBOL
PROGRAMMABLE
MAPPING/
128 TAP FIR
INTERPOLATION
TX_DATA
CSSI