CC1101 channel spacing ,deviation,Datarate，RX filter bandwith 设置问题
你好！
我想请教以下几个问题：
1.RX Filter BW 的设置，我看了DN005 有讲到 BWchannel> BWsignal+ 4· XTALppm· fRF ，这个值大多少才合适，还是刚好等于就可以。太大了会不会影响sensitivity.
2.signal BW信号带宽和DataRate 有什么关系，比如我用4.8K的DataRate, 在GFSK的调制情况下 信号带宽大概是多大，因为确定了信号带宽才能确定RX Filter BW。
同样的Datarate是不是也会根据不通的调制方式而会有不同响信号带宽要求。
3.deviation 的设置是不是根据4· XTALppm· fRF 设置，以提供数据给CC1101 去做频偏补偿。
4.channel spacing 是不是越大越好，还是只要大于信号带宽就可以了，设置时根据什么去考量。
5.对于一般的数据应用 我该选择哪种调试方式比较合适，有没参考资料对比CC1101支持的5终调试方式比较，ASK/OOK除外。
谢谢，希望能得到你的帮助。
看起来专家都比较忙，或者是我的问题太简单。
在这问问题的多数是软件工程师，有几个能真正搞明白呢，搞明白的也去搬砖去了。
问太多，给你个回答就是看参考smart studio有意思吗？
难道真的国外的月亮圆点。唉。
The transmitted signal will have a certain signal bandwidth (BWsignal), which depends on the data rate and modulation format. This bandwidth can be approximated by Carson's rule:
BWsignal = 2*fm + 2*fdev (= data rate + frequency separation)
where
- fm is the highest modulating frequency. 2*fm = data rate
- fdev is the frequency deviation. 2*fdev = frequency separation
BWsignal for 4.8 kbps and +/-25.4 kHz deviation is then approximated as 55.2 kHz
BWsignal for 10 kbps and +/-19 kHz deviation is then approximated as48 kHz
On the receiver side there is a channel filter, which is centered on the down-converted received RF frequency, i.e. the intermediate frequency (IF). The channel filter has a programmable bandwidth BWchannel. The signal bandwidth has to be less than the receiver channel filter bandwidth, but we also have to take the frequency error of the transmitter and receiver into account.
If there is an error in the transmitter carrier frequency and the receiver LO frequency, there will also be an error in the IF frequency. For simplicity assume the frequency error in the transmitter and receiver is equal (same type of crystal). If the receiver has an error of –X ppm and the transmitter has an error of +X ppm the IF frequency will have an error of +2*X ppm (CC11xx uses low side LO injection). Conversely, if the receiver has an error of +X ppm and the transmitter an error of -X ppm the IF frequency will have an error of -2*X ppm.
BWchannel has to be larger than the maximum signal bandwidth BWsignal plus the maximum frequency error due to crystal inaccuracies. Worst case scenario will be for the crystal errors on Tx and RX side to be of opposite signs
BWchannel > BWsignal + 4* XTALppm* fRF
where
- XTALppm is the total accuracy of the crystal including initial tolerance, temperature drift, loading, and ageing
- fRF is the RF operating frequency.
BWsignal is more or less equal for the 4.8 kbps and 10 kbps cases above and can have the same frequency error. The deviation is set to get the same signal bandwidth and thus the same crystal accuracy requirements for the two data rates.
The crystal accuracy, assumiing operation at 868 MHz, will be roughly 15 ppm for the 2 cases above: 4.8 + 2*25.4 + 15*868 = 108 kHz.
Finally: For a fixed RX filter BW, sensitivity vs separation/datarate decreases with about 1.5-2.5 dB per halving down to a certain limit where the loss increases very fast. Thus, you can trade sensitivity for crystal accuracy. (crystal cost)
http://e2e.ti.com/support/wireless_connectivity/f/155/t/180039.aspx
砖家都比较忙，我的问题太简单。
The transmitted signal will have a certain signal bandwidth (BWsignal), which depends on the data rate and modulation format. This bandwidth can be approximated by Carson's rule:
BWsignal = 2*fm + 2*fdev (= data rate + frequency separation)
where
- fm is the highest modulating frequency. 2*fm = data rate
- fdev is the frequency deviation. 2*fdev = frequency separation
BWsignal for 4.8 kbps and +/-25.4 kHz deviation is then approximated as 55.2 kHz
BWsignal for 10 kbps and +/-19 kHz deviation is then approximated as48 kHz
On the receiver side there is a channel filter, which is centered on the down-converted received RF frequency, i.e. the intermediate frequency (IF). The channel filter has a programmable bandwidth BWchannel. The signal bandwidth has to be less than the receiver channel filter bandwidth, but we also have to take the frequency error of the transmitter and receiver into account.
If there is an error in the transmitter carrier frequency and the receiver LO frequency, there will also be an error in the IF frequency. For simplicity assume the frequency error in the transmitter and receiver is equal (same type of crystal). If the receiver has an error of –X ppm and the transmitter has an error of +X ppm the IF frequency will have an error of +2*X ppm (CC11xx uses low side LO injection). Conversely, if the receiver has an error of +X ppm and the transmitter an error of -X ppm the IF frequency will have an error of -2*X ppm.
BWchannel has to be larger than the maximum signal bandwidth BWsignal plus the maximum frequency error due to crystal inaccuracies. Worst case scenario will be for the crystal errors on Tx and RX side to be of opposite signs
BWchannel > BWsignal + 4* XTALppm* fRF
where
- XTALppm is the total accuracy of the crystal including initial tolerance, temperature drift, loading, and ageing
- fRF is the RF operating frequency.
BWsignal is more or less equal for the 4.8 kbps and 10 kbps cases above and can have the same frequency error. The deviation is set to get the same signal bandwidth and thus the same crystal accuracy requirements for the two data rates.
The crystal accuracy, assumiing operation at 868 MHz, will be roughly 15 ppm for the 2 cases above: 4.8 + 2*25.4 + 15*868 = 108 kHz.
Finally: For a fixed RX filter BW, sensitivity vs separation/datarate decreases with about 1.5-2.5 dB per halving down to a certain limit where the loss increases very fast. Thus, you can trade sensitivity for crystal accuracy. (crystal cost)
http://e2e.ti.com/support/wireless_connectivity/f/155/t/180039.aspx
Bruce,
看来你对射频原理非常感兴趣，希望了解得更深一些。 TI的App Note 里面有一些零碎的信息可以了解。不过 Rx BW, Deviation, Data Rate, Modulation 之间的关系是比较普适的，不随具体的芯片变化。这些关系也可以去查阅一些书籍深入了解。下面是我的理解供你参考：
1. Rx BW 一方面需要 > 2 * Deviation + 4 * Freq. Error, 另一方面 Rx BW越大，噪声进来就越多，所以会损失灵敏度。所以理论上是刚好 2 * Deviation + 4 * Freq. Error。但是 Freq. Error 是随温度，晶体，晶体老化(Aging) 变化的，所以需要考虑一定的容余。
2. Rx BW 和 Symbol Rate 大概是2倍的关系。注意不是 Data Rate，因为 4-GFSK 下 Data Rate = 2 * Symbol Rate。
3. Channel Spacing 从防止互相干扰考虑肯定是越远越好，但是考虑到频谱利用率的问题，太大自然可用频道就少了。
4. 为最好的距离表现和抗干扰表现，原则上是越小越好。为省电，是越大越好。
mark!
这是老外回答的么，这么耐心。。
这里支持的都是TI中国的技术团队成员。
Nutcracker 感谢你的回复，你是对的，这些是通用的RF问题。
4. 为最好的距离表现和抗干扰表现，原则上是越小越好。为省电，是越大越好
这条指的是Channel spacing还是Rx Bw filter？
感谢！
Bruce,
应该是Channel Spacing.
modulation BW 在测试EN300220里面的指标！测试没有过！我该怎么调整啊！着急啊！
hi Nutcracker ：
看了你的回复，我有几点疑问：
1.你的回复是说：Rx BW 一方面需要 > 2 * Deviation + 4 * Freq. Error，但Carson's rule:BWsignal = 2*fm + 2*fdev (= data rate + frequency separation)。到底以哪个为准？
2.根据这个公式，再结合BWchannel > BWsignal + 4· XTALppm· fRF 。再来回头看Smart RF studio中CC1310的设置，我发现RX BW和这些公式对不上啊。
比如：868M，50Kbps Symbol rate，25K deviation，晶振10ppm。那么根据Carson's rule，BWsignal = 50K + 2*25K = 100K了，而CC1310 在50Kbps下的RX BW设置为了98K < 100K，这又是为什么呢？ 200Kbps也是同样的情况
如果根据你的公式，得出BWsignal = 50K，加上4· XTALppm· fRF，还算比较接近98K。
可是再看300Kbps，400Kbps的RX BW值，根据你的公式，得出BWchannel 大概在250K-300K左右，但实际CC1310在这两个速率下的RX BW设置为了622K，为什么要大这么多？
以上，还麻烦帮忙解答一下，谢谢！