Image Rejection and QEC of AD9262

Hi,

The application is an Ultra Wide-Band Direct Conversion Receiver (400MHz-6GHz) for a Spectrum Analyzer utilizing the ADL5380 and AD9262.

The datasheet for ADL5380 states it's Image Rejection (worst-case) is -46 dB @ 3.6GHz.

1) I am interested in knowing how much the AD9262's QEC algorithms help improve the Image Rejection / Distortion caused by I/Q imbalance and DC offset?

2) Is the QEC (if enabled) automatically done or does it require calibration from known RF inputs?

3) Worst case convergence time/number of samples of the QEC?

Requirement we are attempting to meet SFDR of >80dBc.

We have the capability to do this in DSP however, we are hoping that the AD9262 removes that design effort.

Thanks

  • Hello,

    The image rejection that one achieve will depend on the bandwidth of the baseband signal as well as the added effects of any amplitude ripple and group delay variation caused be a baseband I/Q filter.  

    Answers to your questions are as follows:

    1) See attachement.  For a single-tone calibration, 100 dB of QEC is possible but this can degrade towards 60 dB for  a wideband signal (i.e. WCDMA)

    2) Once the QEC is enabled by writing to register 0x101, the algorithm is constantly tracking the DC offset and quadrature errors.  One of the channels is used as a reference and correction is added to the second channel to minimize the error between the two channels. Only when you freeze the coefficients or disable the correction does the automatic correction stops.  In the customer’s application when the phase correction is no longer necessary then he can either disable the phase correction and only keep the gain and DC correction on or freeze the phase coefficient.  This is done by writing to register 0x112.

    3) Do not know answer to this question.

     

    To achieve 80 dBFS image-reject performance over the complex bandwidth of 20 MHz, you should employ your own algorithm that accounts for the degradation in SSB performance for wideband signals.

     

    Regards.

    AD9262_QEC_Capability.pdf