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RF2690 参数 Datasheet PDF下载

RF2690图片预览
型号: RF2690
PDF下载: 下载PDF文件 查看货源
内容描述: W-CDMA的接收自动增益控制和解调器 [W-CDMA RECEIVE AGC AND DEMODULATOR]
分类和应用: 电信集成电路信息通信管理
文件页数/大小: 16 页 / 261 K
品牌: RFMD [ RF MICRO DEVICES ]
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Preliminary  
RF2690  
Application Notes  
Voltage Gain Measurement Set-up  
The evaluation board uses a unity voltage gain Op-Amp to simulate the 60kdifferential load impedance condition for  
the chip. The 50output impedance of Op-Amp makes the use of a 50spectrum analyzer power measurement possi-  
ble. The power gain measured will be considered as RAW Gain. The input impedance of the chip is 500differential by  
adding a parallel 680resistor. The input transformer matches 50to 500and results in 10dB difference between  
voltage gain and power gain, hence, the voltage gain of the chip is RAW Gain minus 10dB. Because the input trans-  
former loss is 0.8dB, it needs to be added to the gain. Since the Op-Amp has the unity voltage gain, the voltage at the  
evaluation board output is the same as the voltage at chip I or Q output. Therefore, the voltage gain of the chip with 60kΩ  
load can be calculated by  
Gv=RAW Gain-10+0.8(dB)  
Input IP3 Measurement  
The input IP3 measurement is based on a two tone inter-modulation test condition from the 3GPP standard, which spec-  
ifies two tones with offset frequencies at 10MHz and 20MHz. Due to the on-chip baseband filtering, the two tone output  
is attenuated and cannot be seen. Since the only parameter observable is the IM3 product, the input IP3 then is calcu-  
lated by  
IIP3=Pin+0.5*(Pin+RAW Gain-IM3)  
7
Noise Figure Measurement  
The noise figure measurement is based on the noise figure definition NF=NO-NI-Gain, where NO is the output noise  
density, NI is the input noise density (-174dBm/Hz when no input signal is applied) and Gain is the RAW Gain. The out-  
put noise density NO is measured at 1MHz offset when no signal input is applied. The NF is calculated by NF=NO-  
174dBm/Hz-RAW Gain. Since the I and Q re-combination will provide 3dB extra for signal-to-noise ratio, the actual  
noise figure is should be reduced by 3dB. In addition, noise figure should be reduced by the input transformer loss of  
0.8dB. Therefore, the NF is calculated by  
NF=NO+174-RAW Gain-3-0.8(dB)  
1dB Gain Compression Point Voltage at Baseband Output  
The device has a relatively constant 1dB gain compression point versus VGC. Gain compression is tested with a CW sig-  
nal with 60kload differential.  
How to Calculate the Power Gain of the Demodulator  
In the system analysis for cascaded gain, noise and IP, it is often required to calculate the power gain of the demodulator  
chip itself in matched load condition. Below is an example on how to determine this power gain value.  
For this example, the load impedance is 60kdifferential, the output AC impedance of the I or Q port is 500, the mea-  
sured RAW Gain is 95dB.  
First, the power gain from the input of the chip to the input of Op-Amp needs to be calculated. Since the voltage at the  
50load and the voltage at Op-Amp input are the same, the difference of the power gain across the Op-Amp is the ratio  
of load impedances. Hence, the power gain to the Op-Amp input is 95dB-10log(60000/50)=95-30=65dB.  
Second, the power gain of the demodulator itself with matched load is calculated. The mismatch coefficient a is deter-  
mined by the mismatch coefficient equation  
4RSRL  
(RS + RL)2  
4 500 60000  
-------------------------------------  
= –15dB  
-------------------------  
α = 10log  
= 10log  
(500 + 60000)2  
Rev A4 010918  
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