Its basic function is to pick up the narrowband signals from the broadband & high speed digital signals , and transform it to the baseband . then the low speed baseband signals are sent to the following dsps for processing 其基本功能是从输入的宽带高速的数字信号中提取所需的窄带信号,将其下变频为数字基带信号,并转换成较低的数据率,以供后续的dsp作进一步的处理。
Here we try out a hard way with video card to realize it . in the second place , we discuss some ways of digital modulation in transmission of image data , for example bpsk , qpsk , qam , and so on 随后，针对qpsk ，详细讨论了其基本原理和具体的实现算法，并进行了仿真验证，然后选用hsp50215数字上变频芯片和hsp50214b数字下变频芯片，设计了数字调制、解调器的实现方案。
The interchange is unable to change characteristic of the system , but it can decrease operation greatly . we can quantitatively calculated the reduced computational complexity by using multiphase filter and put forward the model of digital arithmetic 这种互换不会改变系统特性，却大大减少了运算量，定量的证明采用多相滤波减少的计算量，并由此提出了数字下变频的数字化算法模型。
The receiver unit mainly consisted of the digital down converter , matched filter , integration and dump module , power detector , symbol tracking processor , differential demodulator , parallel - to - serial conversion module , output processor and afc module 接收部分主要有数字下变频、数字匹配滤波器、积分清洗、功率检测、符号跟踪处理、差分解调、并串处理、自动频率跟踪处理等模块。
This paper discusses the verification of this digital down converter design and gives testing results . the author of this paper has realized a digital down converter in altera ’ s eps40f1020c5 fpga and this digital down converter has a very good performance 论文作者和其所在课题组的成员共同在altera的fpgaep1s40f1020c5中实现了性能优异的单通道数字下变频器,达到了良好的下变频效果。
While the all - pass network for equalizing improves the precision of signal transmission . at last the circuitry realization ? some test data and trouble shooting are presented . the measure results are much better than the product of the other institute 下变频系统的群延迟均衡器，采用全通网络电路来实现，采用ansoft的serenade软件对其进行仿真与优化，该设计提高了系统传输信号的准确度。
In this paper , variant metering methods are taken in terms of the different features of the analog signal and the digital signal . the rf signal is attenuated and down converted to intermediate frequency and then transmitted to the digital circuit 本课题针对模拟和数字电视信号的不同特点采用了不同的测量方法，在对射频信号进行衰减和下变频处理后的中频信号经过模数转换后，进入数字电路处理。
By the tuner , the dvb - t signal received has been converted to the if signal , and then demodulated by the cofdm demodulation chip . in the end , the usb controller sends the ts ( transport stream ) to the pc where it is decoded by the software 接收到的dvb - t信号经调谐器进行下变频处理后输出中频信号,再进行cofdm (编码正交频分复用)解调,得到的ts码流信号通过usb控制器送入pc机中进行软件解码播放。
At last , simulate the work of the digital down - convert frequency in ideal instance and in instance of existing timing error , carrier error , intersymbol interference . these simulation results prove that the structure of digital down - convert frequency is right 最后仿真了所设计的数字下变频结构在理想情况下和存在定时误差、载波误差、交叉串扰情况下的工作情况，证明了所设计的数字下变频结构是正确的。
This paper focus on the key techniques of digital spread and despread spectrum communication system , which includes high speed adc of digital if , digital down converter , digital pn code matched filter and carrier recovery of digital demodulation 本文结合stel - 2000a对全数字化扩频、解扩中的关键技术进行了研究。主要包括数字中频中的a / d变换、数字下变频、数字匹配滤波器以及数字化解调中的载波跟踪技术等。
