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GC3021A-PQ 参数 Datasheet PDF下载

GC3021A-PQ图片预览
型号: GC3021A-PQ
PDF下载: 下载PDF文件 查看货源
内容描述: 3.3V混频器和载波去除芯片 [3.3V MIXER AND CARRIER REMOVAL CHIP]
分类和应用: 电信集成电路电信电路
文件页数/大小: 38 页 / 269 K
品牌: TI [ TEXAS INSTRUMENTS ]
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GC3021A 3.3V MIXER AND CARRIER REMOVAL CHIP  
SLWS137A  
2.5  
MIXER  
The mixer multiplies the pairs of samples from the input format circuit by sines and cosines and  
outputs the results to the output format and the symbol offset circuits. A block diagram of the mixer circuit  
is shown in Figure 3.  
Round Adder  
Enable Clear  
Add  
2X Gain  
DC_I_IN  
12 Bits  
XI  
(even)  
12 Bits  
Ieven  
Qodd  
Qeven  
From  
ACOS 12 Bits  
Input Format  
Circuit  
12 Bits  
12 Bits  
DC_I_OUT  
12 Bits  
SI  
DC_Q_IN  
12 Bits  
XQ  
(odd)  
Symbol  
Data To  
Symbol Offset  
Circuit  
12 Bits  
BSIN  
12 Bits  
12 Bits  
ASIN  
12 Bits  
12 Bits  
DC_Q_OUT  
12 Bits  
SQ  
Iodd  
BCOS 12 Bits  
Figure 3. MIXER  
The ACOS, BCOS, ASIN and BSIN values are generated by the NCO circuit. In the complex mode  
BCOS will equal ACOS and BSIN will equal minus ASIN. In the high speed mode the ASIN and ACOS  
values are the even time sine/cosine pairs and the BCOS and BSIN values are the odd time pairs. The lower  
11 bits of the 23 bit multiplier products are either rounded off or truncated depending upon the state of the  
round enable control. The rounding is performed using the “round to even” technique1. The 12 bit products  
are passed to the output format circuit.  
The adders sum the individual products to generate complex products. The adder outputs are  
saturated to 12 bits if the add causes overflow. The adder outputs pass through a gain circuit and then to  
the symbol offset circuit. The gain circuit, if it is enabled, doubles the data values. The gain outputs are  
saturated to plus or minus full scale if the gain causes overflow2. The adder clear control allows the Ieven  
and Qeven mixer outputs, instead of the complex products, to be passed to the symbol gain circuit. This  
permits the user to capture the high speed mode’s even outputs in the snapshot RAM, or to use them in the  
phase error lookup circuit.  
DC components before or after the mixer can be removed by adjusting the DC_I_IN, DC_Q_IN,  
DC_I_OUT and the DC_Q_OUT values. These values are added to the input and output data as shown in  
1. When the fraction to be rounded is exactly 1/2, the round to even technique rounds up when the integer portion is odd and rounds  
down when it is even. This removes any DC bias in the rounding.  
2. The input samples of QAM signals have an extra sign bit before the carrier is removed. The extra sign bit is needed because the  
square QAM constellation is spinning. Once carrier has been removed the extra sign bit can be removed by the gain circuit. This  
increases the resolution of the phase error RAM and simplifies the symbol mapping.  
Texas Instruments Incorporated  
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This document contains information which may be changed at any time without notice