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CC1120 - analog FM demodulation
I have a trouble with analog FM demodulation, could somebody help me with these:
1) what are the exact requirements to read data from SOFT_RX_DATA_OUT and enable related trigger clock on GPIO (=CLKEN_SOFT).
Under which condition the CLKEN_SOFT and SOFT_RX_DATA_OUT are available? There will be great any map/diagram/etc. that can clear this.
I run some tests and it seems that clock and data are only available in transparent mode, and I can get minimum clock at about 31kHz (at minimal RX filter BW).
2) What are exact meaning of SOFT_RX_DATA_OUT as user's guide talks about instantaneous frequency offset (in par. 4.1.4) and register description states:
soft-decision symbol data in normal/transparent receiver (p. 100).
It is a software example in http://e2e.ti.com/support/low_power_rf/f/155/t/159307.aspx#579195 that hopefully helps some.
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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?
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.
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?
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.
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We have created a small demo running on the Experimenters board that samples the microphone and sends the "analog sound" using analog FM modulation to a receiver board (a second 5438 experimenters board)
This example uses a setting of 10kbits/s, but using FM audio we end up updating the 160k samples per second (16 x TX bitrate), then on the RX we use 40kHz RX bandwidth which also becomes 160k samples per second (4xRXBW).
Included is a code example of how to make this work.
thank you both Martin for explanation and Thomas for sample code, I'm just going through it.
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?
Software engineer of Unication Co., Ltd (BC, Canada)
The CC1120 is a very flexible device. It can be configured in 4 modes of operation
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)
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 ?
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?
The analog FM feature was included to enable FSK with more than 4 levels and hence 8 bits are used.
Does this sample code suitable for CC1125??
Yes, the CC1120/1/5 are register compatible.
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