CC1120 - analog FM demodulation

It is a software example in http://e2e.ti.com/support/low_power_rf/f/155/t/159307.aspx#579195 that hopefully helps some.

Thank you for your response TER,

Besides the TX in analog FM mode is rather clear to me. The RX analog FM is misty. I already tried the settings from the post above,

but i RX mode I'm able read a baseband? signal on GPIO, but only in transparent mode at rather high rate (~31k).

I wonder about analog FM in RX mode in the similar manner like in TX using SOFT_TX_DATA_CLK, to read instantaneous frequency offset

using SOFT_RX_DATA_OUT as stated in 4.1.4.

Is there any documentation about configuration and meaning of SOFT_RX_DATA_OUT and CLKEN_SOFT?

Many thanks,

Martin

The documentation on this is stated in 4.1.4, page 26 in the userguide.

The CLKEN_SOFT is a signal generated in the modem which is a clock operating on 16x the programmed datarate. For each clock tick the frequency offset given by equation 3 could be read from the register SOFT_RX_DATA_OUT for further processing in the MCU.

Hi TER,

I know in the chapter 4.1.4. but there is unsufficient information about this. In addition there is only "CLKEN_SOFT should be output...", nothing about 16x datarate and even more no information how to enable it.

I tried some experimental settings and I noticed that output CLKEN_SOFT clock is available only with enabled in transparent mode (in MDMCFG0), but as I wrote earlier, the clock frequency si much higher than 16x datarate and depends on BW setting, of course. The minimum clock frequency of CLKEN_SOFT is 31.200kHz with CC1120.

What is the register setting to enable CLKEN_SOFT to generate 16x datarate?

Thank you

Martin

Hi Martin

First of all I know this is a pretty late reply. You may already have sorted this out. But here is a few comments anyway.

The CLKEN_SOFT does not go at 16x data rate. It asserts at the same rate as the programmed data rate. E.g each time it asserts, a new sample is available in the SOFT_RX_DATA_OUT register.

IIf you ave not disabled SYNC search (SYNC_CFG0.SYNC_MODE = 0) the CLKEN_SOFT signal will not be output before a valid sync word is detected. 

Hello,

thank you both Martin for explanation and Thomas for sample code, I'm just going through it.

Martin

Hi,

     After I  viewed the demo code, here are some questions:

Question:  1. Does CC1120 handles the FM modulation and demodulation ?

                    2. SOFT_RX_DATA_OUT register is the discrimination data of the demodulated audio signal?

Thanks,

Robert  

Software engineer of  Unication Co., Ltd  (BC, Canada)

Robert, 

The CC1120 is a very flexible device. It can be configured in 4 modes of operation

• Full RF modem with use of FIFO (with CRC, framing, etc)
• Synch Serial mode (data is decoded and provided bit by bit
• Asynch Serial mode (data is not decode, it is provided at 16 times the setup bit rate and you have to discriminate externally)
• "Analog FM" (an instantaneous frequency offset is provided at 4 times the RX bandwidth)

Regards
/TA 

Hi TA,

       Thanks for quick reply. Here is another question.

      Q1:  Is there any document details how to use  CC1120 in Analog FM mode ?

        (Except section 4.1.4 in SWRU295C user's guide), there is no details about  how to use Analog FM mode)

Robert

As our test, we obtained the demodulated audio data from SOFT_RX_DATA_OUT register by reading with SPI port.

Hare are questions:

Q1: Is it the discriminator output? please confirm it.

Q2: What is maximum data frame rate that could be used to retrieve data from SOFT_RX_DATA_OUT ?

Hi TA,

Analog FM is one of requirement to our new product. The SOFT_RX_DATA_OUT register could provide the discriminator output (we done the test on CC1120DK development kit). Sine SOFT_RX_DATA_OUT only has 8-bits resolution; it is too low for our application.  

Question: Does CC1120 could provide the discriminator output with 16 bit or more resolution?

Thanks ,

Robert Lin

The analog FM feature was included to enable FSK with more than 4 levels and hence 8 bits are used.

Hi

Does this sample code suitable for CC1125??

Thank you

Lee Chang-Yun, 

Yes, the CC1120/1/5 are register compatible.

Regards,
/TA