We don't have a reference design for this frequency band. You should be able to get good performance if you use the 169 MHz design and adjust this some if needed. 

For channel size 6.25 kHz you have to use CC1125, minimum RX bandwidth on CC1121 is ~41 kHz. We don't have a SOC that covers 220 MHz. 

Hi,

CC1125 looks like a great chip for my application.

1) You suggested to use "the 169MHz design".  Are you referring to an Eval Board/Kit?  If yes how do I find this?  I'd like to have a schematic of that eval board too.

2) The description of the chip says the chip contains all the filters.  Do I understand that all that's needed is a balun at the Rx and what ever filtering at the Tx port and I need to change that from 169MHz to 220MHz?

3) Looks like I simply connect my Power Amplifier to the Tx output.  Do I need to connect a LNA to the Rx input or is the NF low enough and the gain sufficient to achieve good receiver sensitivity?

4) If what I said in 3) above is true, I need a Tx/Rx SPDT switch to connect the Tx and the Rx sections to the antenna.  The CC1125 seems to provide an output to control the switch,  Figure 5.1 of the CC1125.pdf datasheet shows no Tx/Rx switch, just a connection from the TRX_SW pin to the middle of the RF, is this really how this is done?  Looks like I need to supply DC power at the PA port, how much DC?.  The LNA ports are differential and requires a balun and  the PA port single ended and does not require a balun (did I get this right)?

5) It looks like the CC1125 has a built in Baseband Processor.  I just need to connect serially to it with a UART and send my data and it will packetize it, create a preamble, and send the data with some modulation like FSK or GFSK, etc.  Does it do some baseband filtering or pulse shaping (like a raised cosine filter shaping the pulse for example)?   How do I chose the modulation and how do I set registers in the CC1125 (any document for that)?  Is there any form of Error Correction (FEC) ?

6) Do I need to design a loop filter for the synthesizer or is this already done and covers my 220MHz- 221MHz band?  What is the step size (i.e. when I change frequency)?   

Thanks,

Jeff

1) I'm referring to http://www.ti.com/tool/cc1120em-169-rd

2) The PA and the LNA have a optimal load/ source impedance at different frequencies. The one we have measured/ calculated is given in the datasheet. The component values from the 169 MHz design will be close to optimal but to get the last dB you should probably select values midway between the 169 Mhz design and this http://www.ti.com/lit/an/swra398a/swra398a.pdf

3) This is dependent on which FEM you are using etc. If you look under reference designs under http://www.ti.com/product/cc1120 (http://www.ti.com/tool/cc112xsky65367em-rd) you will see some ways to do it.

4) The TRX_SW pin is high impedant in RX and tied to ground. Some FEMs also has a built in switch. Please check the ref design for required external components.

5) CC1125 does not have a FEC. The easiest way to set the registers is to use Smart RF Studio (http://www.ti.com/tool/smartrftm-studio) How to set modulation etc is also described in the UserGuide.

6) No, the loopfilter is build-in except for the 1.8 nF cap that is independent of frequency band.

Thanks.

1) It's a good thing we can setup the registers using the Smart RF Studio software when we use the eval board but ultimately we will have to set the registers of the CC1125 ourselves with an on board CPU in the final design.  I would need to know how to interface with the CC1125 registers, a list of the registers would be very useful with the fields whowing the different ways to set them.

2) Please confirm my understanding of the system:  I interface with the CC1125 using a simple serial interface and set it to a certain frequency, Tx power level and modulation.  Next I send the data to it at a given datarate like 19.2kbps for example using the same serial interface and the CC1125 will segment my data into smaller packets add a preamble and send the packets to the other CC1125 on the other side of the RF link.  The other CC1125 which is receiving will detect the preamble, set the Rx gain using a built in AGC loop sequence, receive the data payload of each packet, reassemble the packets and generate the original 19.2kbps data stream I sent.  Is this how it works or do I need a whole other SOIC or Baseband Processor to achieve this?

3) Do you have suggestions for FEMs at 220MHz?  Specifically we will want to go to higher power levels (like Pout = 2W and 4W).

1) Note that with Smart RF Studio you can export all registers to a file, typically a .h. Then these settings can be used in your code. Please check http://www.ti.com/litv/zip/swrc253b (the easy link example is a good place to start)

2) I believe the software examples will give you an idea here.

3) Check with Skyworks or RFMD.

1) Is CC1125 superheterodyne or direct conversion.

2) Is the baseband signal at a certain IF or is it at baseband (0Hz)

3) Can I set the channel bandwidth filter?  Our channels are 6.25kHz / 12.5kHz / 25kHz.

4) Can I use the serial interface to read and right to registers in the CC1125?

5) How many registers are there in the CC1125?

You can easily find answers to all of these questions looking at the datasheet and UserGuide

1) See the block diagram in the datasheet.

2) For low datarates (as in your case) use the default IF frequency.

3) If you look at SmartRF Studio and the UserGuide you will see that you can get all 3 bandwidths setting the CHAN_BW filter.

4) As the software example I linked to show you use the SPI interface to read/ write al registers.

5) Note that you don't need to use a lot of the registers on CC1125 since they should be kept at their reset values.

1) The block diagram shows direct conversion with I and Q separation on the Rx (low pass filters which normally means zero IF) but shows no conversion on the Tx.  Does it mean the Tx has no frequency conversion and is just the LO being modulated for OOK and ASK - but what about FSK and GFSK on the Tx there should be an upconversion there but the block diagram does not show it?

2) Not sure if you sent me the User Guide already - what is the name of the file for that?

3) How many registers are there in the CC1125?

The UserGuide is here: http://www.ti.com/litv/pdf/swru295e

For 1) and 3): Could you give some background for these questions? For development a system with CC1125 the number of registers are not relevant.

Thanks - You're right the user guide has all the answers about the SPI interface and the registers.  The CC1125 is not only a transceiver but it has a full blown baseband processor in it and is perfect for our application.

1) The Development Kit I found (CC1125DK) has 2 radio cards in it but the frequency is 869MHz.  Is there any other Development Kit with radios that are closer to 220MHz (like 169MHz) ?  If not I guess we can just change the RF components to make it work at 169MHz using the 169MHz reference design schematic or at 274-320MHz using the 274-320MHz reference design schematic or go to in between frequencies using in between components as you explained before.

2) Can I buy the little radio cards (CC1125EM-CAT1-868) seperately?  I did not find them on the internet (Digikey, Mouser, Findchips.com).

2) If I implement the 169MHz or the 274-320MHz reference design, is the RF port 50ohm or 75ohm?'

Thanks very much for the help.

Jeff

1) It depends on the soldering equipment you have at disposal. To start with I would try these: http://www.ti.com/tool/cc1120emk-169. CC1120 covers 12.5kHz channels but not 6.25 kHz. Do your initial testing on CC1120 and if the performance is as expected get CC1125 samples and change the chip. CC1120 and CC1125 are pin and software compatible so a lot of development could be done on CC1120 before switching to CC1125.

3) The antenna port  is 50 ohm.

Thanks.

I was able to find the CC1120EMK-169 which is closer to my frequency of 220MHz.  This is a kit that has 2 radios and 2 antennas but no TrxEB (so the kit is incomplete it seems).

The closest complete kits I found were the CC1120DK and the CC1125DK but these kits are 915MHz and 868MHz respectively.

1) Do the radios on the CC1120EMK-169 Evaluation Module Kit have the exact same PCB for the RF module as the CC1125DK / CC1125DK but with different RF components or is it that the PCBs are also different from one kit to the other for the RF module ?

2) Where can I get the schematic (and BOM) of the TrxEB board - I'd like to use your MSP430F5438 MCU. 

1) They uses the same PCB

2) See http://www.ti.com/lit/ug/swru294a/swru294a.pdf

Thanks !

Ok - we have the development kit now (868MHz).  We are using the CC1125 (CC1125DK).

1) How do you change/control the center frequency?

2) What is the smallest step size in frequency?  An example of channel we need to produce is 220.0025MHz.

3) How do we know how much bandwidth we occupy in the channel for a given modulation (other than using a spectrum analyzer - is there a table linking the settings and the resulting signal bandwidth)?

Thanks,

Jeff Rivard

1) and 2) See Section 9.12 in the UserGuide

3) For FSK a rule of thumb is OBW=datarate+2*deviation. For GFSK less.

Hi,

Thanks - This shows us how to program a different frequency - But I want to know how to change the frequency using the RF Studio software (not programming).  Thx

Can you provide us with the source code of the sw running on the Development Kit?

Thanks !

Source code: http://www.ti.com/litv/zip/swrc219b

For the frequency in Studio: Under Carrier Frequency you type in the frequency you are interested in. Studio will round to the closest frequency possible with the selected crystal frequency.

Hi,

We bought the 868MHz Development Kit:  CC1125DK.  It comes with two 868MHz radios but these radios have a SAW filter on them (U3 = EPCOS 3749).  This SAW filter appears in none of the schematics I have (i.e. I could not find a schematic with a SAW filter like the radio I purchased).

My ultimate goal is to recenter the design at 220MHz.  I was suggested by TI to use the 169MHz and the 274MHz reference design schematics and use in between values of inductors and capacitors as a starting point.

I now have all 3 schematics:  868MHz, 169MHz and 274MHz.  None of these schematics are the same as the PCB of the radio I purchased since none of them have a SAW filter.

1) Why do you put a SAW filter on that reference design? Finding a SAW filter at my new frequency is not simple.  Is this the kind of filter I need for a design at 220MHz (also, SAW filters are lossy and I'm used to them at IF to define the channel, not at RF)?

2) Do you have the schematic of the radio that I bought with the Development KIt (i.e. CC1125DK, 868MHz with SAW filter).

3) How do I buy a radio ("Development Kit Evaluation Module") I can plug in my kit that will correspond to the 169MHz and the 274MHz schematics I have (none of the schematics I have include a SAW filter).  Basically I was thinking of not using a SAW filter and stick to designs like the 169MHz and 274MHz.  I need the part number of the radio and a schematic corresponding exactly to what I'm going to buy.

Thanks,

Best regards,

Jeff

I believe that you have gotten EMs based on this reference design: http://www.ti.com/tool/cc1125em-cat1-868rd. The SAW filter is included in RX to comply with ETSI CAT 1. For your design you don't need a SAW filter.

As posted before http://www.ti.com/tool/cc1120emk-169 is a good startingpoint.

The offerings we have could be found here:

http://www.ti.com/product/cc1120

http://www.ti.com/product/cc1125

Hi,

We have bought the CC1125DK.  We found that the radios have SAW filters on them.  None of the schematic you gave us have a SAW filter.

We tried looking at the CC1125EM-CAT1-868RD Reference Design link but this link goes no where (a TI page with apologies saying that the page no longer exists or something).

1) We would like to have the schematic of the SAW filter based radio we purchased.

2) We want to buy radios with a PCB that has no SAW filter and corresponds to the 169 and 274MHz schematics.  The CC1120EMK-169 seems to be an example of such a design as you posted above but we have 2 questions regarding this:

i) Are we certain that the CC1120EMK-169 has no SAW filter and corresponds to a known schematic?  Please provide the info for this schematic if it is available.

ii) Can we purchase a radio card that would have no SAW filter and would have the CC1125 on it?  Please provide the info for this if it is available.

Thanks,

Jeff

1) Sorry about the link. Sometimes the links are broken for whatever reason.3580.CC1125_Cat1_EM_SCHEMATIC.pdf See attached for the schematic.

2) The CC1125EM-CAT1-868RD Reference Design is the only EM we have with a SAW filter. It is also the only boards we sell with CC1125 on.

For schematic for the 169 MHz design see http://www.ti.com/tool/cc1120em-169-rd / http://www.ti.com/lit/zip/swrc220

Thanks,

So if we order a CC1120EMK-169, it will have no SAW filter right?

We can simply exchange the CC1120 with a new CC1125 and the Development Kit is going to work just the same right?

Best regards,

Jeff

The 169 MHz EM does not have a SAW filter.

The only thing you have to do is to exchange the CC1120 with a CC1125 and you will be up and running.

Hi

We bought the CC1125DK it came with two 868MHz radios cards.

 Is the following reference design a radio card that will connect perfectly to our kit:

 CC112x SKY65367 EM 30 dBm 169 MHz Reference Design

I noticed that unlike other Eval Modules this one does not use the TRX_SW line coming out of the CC1125.  Is this going to work seamless with the regular TrxEB boards we have from the CC1125DK and also the regular software that comes with it?

Why is it not using the TRX_SW line?

Thanks,

Jeff

The CC112x SKY65367 is supported by TRXEB, chose this board from the range extender menu in SmartRF Studio.

The TRX_SW line is required when the TX and RX path are combined to one SMA contact/ antenna. FEMs like the SKY65367 have separate RX and TX inputs/ outputs towards the transceiver and the TRX line is not required. 

I see that the CC112x SKY65367 is using an external Tx / Rx switch (which is part of the Skyworks PA chip).

The Tx / Rx switch still requires a control line.  On the Skyworks PA chip (SKY65367-11) there is an input to control the switch called CTX.  The CTX pin is connected to GPIO0 on the CC1125 (Pin 10).

This means GPIO0 will send a level 0 or 1 depending if the radio is in Tx mode or Rx mode (GPIO0 has to replace TRX_SW).

Is GPIO0 a I/O port dedicated to Tx / Rx?

When we do our own design maybe we can use TRX_SW instead of trying to control GPIO0 (the chip is constantly disturbed every Tx / Rx cycle to take care of GPIO0).

Thanks,

Jeff

It is not recommended to use the TRX pin to control a FEM or a RF switch. The TRX pin does not provive a logic signal sisnce it is pulled low in TX and open in RX.

Is GPIO0 a I/O port dedicated to Tx / Rx?

If we connect the TRX_SW to a pull up resistor can we use it?

Hi,

We want to order both 169MHz Evaluation Module Radios:

1) CC112x SKY65367 EM 30 dBm 169 MHz Reference Design

2) Regular Eval Module 169MHz Radio (without Sky65367)

We need to know the exact MODEL NUMBER of these products so we can order them through Mouser or Digikey.

Please provide these model numbers.

Best regards,

Jeff

1) This is a reference design and boards are not for sale.

2) Search for CC1120 at the websites in question. They are called CC1120EM 169. It is just one EM on 169 MHz so it should not be possible to pick wrong product.

On the Reference Design, what is the role of R171 and C173?

Thanks,

Jeff

R171 is to lower the bias point of the PA, typically at max voltage, for reability reasons. If removed the voltage will be too high and the performance will be degraded over time. C173: Providing better AC grounding at the node between resistor and inductor for slightly higher power out.

How much DC current (bias) is going through R171 (i.e. entering Pin 17 of the CC1125)?

Thanks,

Jeff

I'm building a WSN node with the help of MSP430 and CC1121. can you help me to get the 

1) Proper reference design of CC1121 for 868-915MHz 

2) Antenna design for above radio

3) Reference design or material for interfacing MSP430F5437A with CC1121

Thanks in advance!

please see http://www.ti.com/tool/cc1121em-868-915-rd for the reference design . 

please see the antenna selection guide AN058 for different possible antenna designs for your design http://www.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=swra161b

Please refer to the SW examples for 3) http://www.ti.com/product/CC1121/toolssoftware