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CC1125 Sensitivity specification

tony holt
Prodigy 200 points

Other Parts Discussed in Thread: CC1101, CC1125, CC1120

Comparing the sensitivity figures of the CC1125 and the CC1101 I see they are specified differently: the CC1125 figures are for a 1% BER whereas those for the CC1101 are at 1%, 20 byte packet error rate. I calculate the latter to 1% of 20 * 8  = 160 bits which is a BER of 6.25 x 10^-5.

Looking at some BER/SNR plots for FSK it appears to mean the CC1125 sensitivity figures need to be reduced by about 5dB to be comparable to those of the CC1101.

Is this correct or am I missing something obvious? What value should I be using to adjust for the differing BERs? I'm most interested in 38.4kb/s GFSK at 434MHz where the specified values are -110dB (CC1125), -104dB (CC1101) which would mean very similar sensitivities.

Thanks,

  Tony H

  • 0
    TI__Guru**** 317180 points

    Instead of potentially getting lost in the math I measured one board (CC1120, 433MHz, 38.4kbps, 20kHz dev, 2GFSK):

    20% PER, 3byte payload: -110dBm

    1% PER, 20 byte payload: -106.5dBm

  • 0 in reply to TER
    Prodigy 200 points

    Thanks for the prompt response.

    So a 3 byte payload means a 7 byte packet (address + length + 3 bytes payload + 2 x CRC)?

    If so, I calculate the respective BERs to be:

      1/(100/20%) * 7 * 8 bits) = 3.6 x 10 ^ -3

      1/(100/1%) * 24 * 8 bits)  = 5.2 x 10 ^ -5 (I forgot the 4 byte overhead in my first post)

    Looking at a 2-FSK theoretical BER versus SNR plot (Fig 3.17, page 62) that I found in http://www.dtic.mil/dtic/tr/fulltext/u2/a190028.pdf, the SNR difference for the above BERs is 3.3dB which is close to the 3.5dB you measured. (The legend says FSK/QPSK but the text on the previous page makes it clear its for 2-FSK).

    So looking at the SNR for the 1% BER used in the CC112x specs, it seems reasonable to subtract 4.5dB from the CC112x sensitivity figures when comparing with those from the CC1101 specs.

    Or have I got it wrong?

    Tony H

  • 0 in reply to tony holt
    TI__Guru**** 317180 points

    3 byte payload = 3 byte payload + CRC. Fixed lenght packet, no address. This implies that 20% PER, 3 byte packet equals 1% BER.