Short Range Wireless Continues from page 49
signal was run through the digital data path and looped back indirectly to the DAC cores. Without the programmable filters active in Figure 10, the harmonic at 2fc measured at –73.88dBm. With the PFILT active in Figure 11, not only is the harmonic filtered out but also the noise floor of the data path is reduced and displays the typical Chebyshev out-of-band ripple. Group delay also remained flat in the pass band for the band-pass filter.
Finally, Figure 12 shows the results of the band-pass filter applied to the DAC outputs using the same multitone test vector. The pass band increases the noise
floor by 4.2dB but reduces the noise floor in the stop band by 2dB to 3dB following the common Chebyshev out-of-band ripple.
Figure 9. A MATLAB-generated band-pass magnitude response and group delay compared to implemented filter response in an MxFE PFILT model.
Latency
Latency through the loopback configuration was measured using a hardware test bench with equal length
Table 2. MATLAB Band-Pass FIR Specifications
coax cables. Total latency measured was 500ns.
Tables 3 and 4 show the expected latency for the configuration in which the AD9082 was run. The sum of ADC and DAC rates gives minimum to maximum value. 500ns is observed to lie within this range. Keeping the propagation delay in wireless systems below 1µs is adequate for ensuring negligible impact on overall network latency and maintaining coherency between link partners. This can apply to 802.11b/g, 4G LTE, and even 5G-NR mobile phone synchronisation. Therefore, demonstrating a latency of 500ns ensures that even with digital filter delay, the
Figure 10. An MxFE loopback output. PFILT disabled. 200MHz to 15dBm RFIN.
Figure 11. An MxFE loopback output. PFILT enabled. 200MHz to 15dBm RFIN.
Figure 12. A multitone test vector MxFE DAC output comparison with and without filtering. Compared to MATLAB-generated filter mask. Reference level of –40dBm.
system remains interoperable as a wireless receiver platform for your designs.
Conclusion
(Right) Table 3. DAC Latency Calculations for Given Test Configuration
RF signal chains perform the necessary analogue processing to get your signal from waves to bits. However, hardware- side issues like parasitics and power amplifier nonlinearities as well as wireless challenges like multipathing and fading degrade the quality of the signal and turn the signal chain into a non-ideal transfer function. Compensating for attenuation and spectral losses is an important step to ensure your data is accurate and reliable. Using ADI’s AD9082 MxFE with programmable filtering allows the user the ability to easily design and implement useful filter profiles with sharp transition bands over a wide range of frequencies.
https://www.analog.com/en
(Left) Table 4. ADC Latency Calculations for Given Test Configuration
References
“Evaluating the AD9082/AD9081/AD9986/ AD9988 Mixed-Signal Front-End (MxFE) RF Transceiver.” Analog Devices, Inc., January 2022. “AD9081/AD9082 System Development User Guide UG-1578.” Analog Devices, Inc., July 2021. “Mixed Signal: Section 6.” Analog Devices, Inc.
50 November 2023 Components in Electronics
www.cieonline.co.uk.uk
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