Analog Devices ADRV9001 User Manual page 145

Reference Manual
RECEIVER/OBSERVATION RECEIVER SIGNAL CHAIN
Quadrature Error Correction (QEC)
In an ideal analog mixer, the in-phase (I) and quadrature-phase (Q) sinusoidal signals are orthogonal. In addition, the I and Q paths of LPF
and ADC should have identical frequency responses. However, in reality, IQ imbalance always exists in the mixer, LPF, and ADC, resulting
in quadrature errors. Without properly handling, it seriously degrades reception performance. For IF reception, the respective image mixes
partially onto the desired signal during the IF down conversion. In direct conversion reception, IQ-imbalance leads to a distortion of the
IQ-signals themselves within the respective desired baseband channel.
In general, quadrature error can be classified as frequency independent error (FIE) and frequency dependent error (FDE). FIE is mainly caused
by the mixer I/Q sinusoid mismatch in both gain and phase, while FDE is mainly caused by the inconsistent filter responses.
Because the ADRV9001 supports both the NB and WB modes, NBQEC and WBQEC algorithms are developed accordingly to handle
quadrature errors in these two modes effectively. NBQEC employs a time-domain adaptive algorithm to estimate both the gain and phase
mismatch. Then, estimations are applied to correct the distorted input signal in real-time before passing to DDC. WBQEC designs a correction
filter to cancel the effect of the mismatch filter by modeling the quadrature error generation as a mismatch filtering process. The correction
filter parameters are obtained through the initial calibration by injecting RF tones into the mixer at selected frequencies and then on-the-fly
adjustment by processing the receiver data in real-time.
Digital Down Converter (DDC)
DDC is only used when IF reception is employed. By using a programmable NCO configurable from 45 kHz to 21 MHz, it further converts the IF
signal to the baseband.
Frequency Offset Correction
In a communication system, the transmitter transmits a desired signal at RF over the air. As the clock reference at the transmitter or the
receiver is independent of each other, this can result in the RF carrier frequency offset between the transmitter and the receiver. This frequency
difference is called the carrier frequency offset (CFO). In the receiver data chain, there is a frequency offset correction block to further correct
small carrier frequency offsets in both the NB and WB modes through an API command. The BBIC must estimate and provide the correction
value. The correction can occur immediately or relative to the receiver frame boundary. Another programmable NCO is employed with a
configurable frequency -12 kHz to +12 kHz and frequency tuning word (FTW) 32 bits wide.
The API command adi_adrv9001_Rx_FrequencyCorrection_Set( ) corrects small deviations in the receiver LO frequency. Provide the
frequency deviation value at Hz and specify if the correction should take place immediately or at the start of the next available frame. Note that
the device employs the digital NCO in the datapath to correct the frequency deviation instead of the RF PLL retuning.
Programmable FIR Filter (PFIR)
The PFIR is an optional 128-tap programmable FIR used in both the NB and WB modes. The four sets of customized FIR profiles are stored at
the initialization phase. One of the four stored FIR profiles is switched to and loaded on the fly under the control of the baseband processor.
The PFIR is loaded with a customized low-pass filter profile to reduce the adjacent channel interference, which helps in better channel
selectivity. For more details, see the
Receiver Signal Strength Indicator (RSSI)
RSSI measures the received signal power over a period of time, which is employed to calculate the interface gain to avoid saturating the data
port. In addition, in the Monitor Mode, it performs signal detection in WB applications and works together with the FSK Discrimination block to
detect signals in NB applications.
An API command adi_adrv9001_Rx_Rssi_Read( ) retrieves the measured signal level. The API function reads back the RSSI status for the
given receiver channel and is called any time after the device is fully initialized. The following data structure retrieves the power measurement in
both the milli-dBFS and linear format.
typedef struct adi_adrv9001_RxRssiStatus{
uint16_t power_mdB;
/* Linear power is calculated by this formula: linear power = (mantissa * 2^-15) * 2^-exponent */
uint16_t linearPower_mantissa;
analog.com
Receiver Demodulator section.
/* Power in milli dB */
/* Mantissa of Linear Power */
ADRV9001
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