LMS6002D Receiving performance problem
Posted: Thu May 26, 2016 11:49 pm
I am debugging a system on the bladeRF, the system is something like ATSC. The receiver performance is suffering. I tried lots of configuration of LMS6002D, but cannot find the solution, can you please help to find the problem, or tell me how to debug to improve the performance.
Thanks.
My working environment is as following:
1. the source signal is from RF signal generator, output level -10dbm, the source signal is good.
2. the receiver is bladeRF 115x, with LMS6002D
3. the central frequency is 786MHz
4. the signal bandwidth is 8MHz
5. the RX samplerate is 30.375M
6. the RX part configuration is: RXLNAGain=0db / RXVGA1=5db / RXVGA2=0db
7. the modulation mode is 4QAM
8. We get signal from ADC output of LMS6002D, and probe them by logic analyzer.
After analyzing the probed data, we see there is problem of angle error in receiving signal, but the receiving signal amplitude seems good. As following:
1, The constellation of received signal is shown as below.
From the constellation, it is obvious that there is severe phase noise or phase error. 2, The amplitude of received signal seems good. 3, Observing the phase error, we find that there is large phase variation on the receiving signal and the error signal is a periodic signal. The symbol rate is about 7.5MBaud, so the frequency of the error signal is about 15KHz.
This phase error may degrade the overall C/N performance about 1.5dB. So, our question is where comes from the periodic phase error signal? How can we eliminate this phase error?
Thanks.
My working environment is as following:
1. the source signal is from RF signal generator, output level -10dbm, the source signal is good.
2. the receiver is bladeRF 115x, with LMS6002D
3. the central frequency is 786MHz
4. the signal bandwidth is 8MHz
5. the RX samplerate is 30.375M
6. the RX part configuration is: RXLNAGain=0db / RXVGA1=5db / RXVGA2=0db
7. the modulation mode is 4QAM
8. We get signal from ADC output of LMS6002D, and probe them by logic analyzer.
After analyzing the probed data, we see there is problem of angle error in receiving signal, but the receiving signal amplitude seems good. As following:
1, The constellation of received signal is shown as below.
From the constellation, it is obvious that there is severe phase noise or phase error. 2, The amplitude of received signal seems good. 3, Observing the phase error, we find that there is large phase variation on the receiving signal and the error signal is a periodic signal. The symbol rate is about 7.5MBaud, so the frequency of the error signal is about 15KHz.
This phase error may degrade the overall C/N performance about 1.5dB. So, our question is where comes from the periodic phase error signal? How can we eliminate this phase error?