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CC1190 + CC1101 Ref Design SAW filter question
I have seen in the Preliminary CC1101 + CC1190 Ref Design that was posted in this forum that there is a SAW filter between the transceiver and the front-end. I have not been able to find any information about the purpose of this filter. I assume that it is to reduce spurious outputs from the CC1101 to aid in passing FCC requirements but are there any details available about the issue? Like what frequencies are a problem for FCC? Or is it mainly to prevent interference from pager and cell phone base stations that are nearby the 915MHz band?
The reference design you refer is indeed preliminary and does not come with any documentation. When the reference design is put on the web there will also be a design note with electrical parameters.
As for the SAW filter: This is included in the design to attenuate CC1101 harmonics so that the harmonics emitted by CC1190 (which also includes harmonics generated by CC1190 itself) are below the FCC 15.247 requirements. Please note that the 3rd, 4th, 5th, 6th, 8th, 9th harmonics all fall in restricted bands were the limit is -41.2 dBm. The main concern will be the 3rd, and if the output power is +27 dBm, the harmonic needs to be 68 dB down. This mandates for a SAW filter. Please note that I assume no duty cycle relaxation factor. That is, the transmission lasts for more than 100 ms. [Note on relaxation factor: The spurious emission limit is -41.2 dBm inside the restricted bands, but FCC allows for up to 20 dB higher peak emission if duty cycling is being used. The maximum TX on time must be less than 100 ms to get a benefit from this rule. The relaxation factor is 20*log(TX_ON_TIME/100 ms)]
An added benefit of the SAW filter is the improved out-of-band blocking performance.
Thanks for the quick and detailed response. That is exactly the information I was looking for.
I have seen in swra319 "CC1190 FAQ";
Q: What output power can I expect when using the CC1190 combo boards (EMKs)?A: The CC1101-CC1190- 915 EMK combo board can deliver up to +26dBm and stillmeet FCC part 15.247 regulations. The CC1101-CC1190 868 EMK combo board candeliver up to +20dBm and still meet ETSI EN300 220 Regulations.
I assume the limit of +20dBm@868 is due to more strict spurious limitations in ETSI. Is there any way to use the full +27dBm at 868?
Would it be possible with duty cycling as per FCC?
Sorry for slow response on this.
The CC1101-CC1190 can do +20 dBm in Europe. The limitation is the modulation bandwidth requirements under EN 300 220 (BW between -36 dBm points in the output spectrum). For +27 dBm at 868 MHz you need to use a transceiver with less phase noise
Thank you for the reply. Would +27dBm be possible with the CC1020+CC1190?
So even if SAW filter is used in CC1101+CC1190, it is still impossible to pass European limitations ? (assuming 0.5W ERP and following CC1101+CC1190 reference design).
+27 dBm will be possible with CC1020 + CC1190. Only looked at low data rates (4.8 kbps), but in this case there will be a significant margin to the modulation bandwidth requirements.
The maximum output power is limited by the modulation bandwidth requirements
A SAW filter will not improve on modulation bandwidth as it is too close to the carrier. A SAW filter is still needed though, but this is to attenuate spurs both below and above the carrier.
Thanks for the clarification of the requirements. The CC1190 data sheet shows a connection between the CC1020 and CC1190 with some passives and a SAW. Is there a more detailed schematic showing component values, or even better a CC1020+CC1190 Ref Design?
Hello Sverre,Apparently, C1020+CC1190 could pass European limitations but your main concern is about the modulation bandwidth requirements.However, for what I understand from ETSI EN 300-220, the modulation bandwidth requirement applies only to equipment with a bandwidth above 200kHz. Otherwhise (eg equipement with a bandwidth below 200kHz), it is necessary to be compliant with the adjacent channel power requirements . So, would it still be possible to meet ETSI EN 300-220 by using a channel spacing of 25kHz and 27dBm output power.
To answer your question regarding a CC1020+CC1190 reference design. We do not have such a design, but once the CC1101+CC1190 design is released you can simply change CC1101+balun with CC1020+output/input match.
In Europe you can transmit at +27 dBm in the 869.4 to 869.65 MHz range. The whole band may be used as 1 wideband channel so no need to comply with ACP requirements. BTW: in the new ETSI EN 300 220 narrowband is now =<25 kHz.
Thank you for your quick answer.
Actually, using one wideband channel is not an option for us: we need to use sub-bands in the 869.4 - 869.65 MHZ range (25kHz channel spacing) and I guess ACP applies.
In fact, that is not my main concern and I have a few more questions. We made some tests with the CC1190-868MHz reference design and the output power is close to 20dBm. In the same time, we tried the CC1190-915MHz reference design, but with a transceiver CC1020 configured at 869.625MHz. The power available at the PA output is close
to 27dBm but I guess that the output matching is quite bad.....
So, I have two questions after that:
- How is performed the 20dBm limitation in the CC1190-868MHz reference design??? In fact, there is just a few changes of values between the 915 and 868MHz reference designs, so I am quite lost with that!
- Is it recommanded to use the 915MHz reference design with a transceiver configured at 869MHz? Or is it possible to improve the current consumption by slightly changing the reference design?
Finally, in order to understand the matching network beetween the CC1190 and the antenna, one thing missing in the CC1190 datasheet is the PA load impedance and the LNA input impedance (VS frequency). Do you have these informations ?
Do not hesitate to ask me more informations if it is not really clear.....
Thanks, Sverre. I really forgot to say, that I am going to occupy whole 869.40 - 869.65 band, using only one channel. It's clear now.
Ender, you can see this topic: http://e2e.ti.com/support/low_power_rf/f/155/p/35307/125067.aspx
There are reference designs for CC1101+CC1190, so you dont need to know impedance of the CC1190 input and output. The topology, BOM and everything is given there, so we need just copy all stuff between CC1190 and SMA connector. :)
P.S. sorry if I am saying something wrong.I am just amateur. :)
I already looked at CC1101+CC1190 reference design, but apparently, it can't pass EN 300-220 for our application (sub-bands of 25kHz in the 869.4MHz - 869.65MHZ range and 27dBm output power). That is why I am trying to get more informations.
Hi Ender, I saw that you are having trouble getting passed some the standards with that RF Filter. It can be tough so you may want to check the impedance of what you are going for to see if there is another kind of rf filter you can use. TI has some incredible ones but if you need anything custom done that might be another ball of wax entirely check out some other rf filter references to see if you can get some better specs http://www.oscilent.com/catalog/Category/rf_saw_filter.htm
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