Digital down converters adsl

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Although this down conversion method can realize that with hardware its resource occupation amount is large, the internal system design is complicated. The internal system that the objective of the invention is to cause greatly for the resource occupation amount that solves existing digital down converter method designs complicated defective, has proposed a kind of Wideband Intermediate Frequency signal digital down conversion method. Technical scheme of the present invention is: a kind of Wideband Intermediate Frequency signal digital down conversion method specifically comprises the steps:.

Described step S3 detailed process is as follows:. Wherein a t is the envelope information of input signal, Be the phase information of signal, f 0 Be carrier frequency. Obtaining sample sequence is:. In the formula:.

Be x[n] in-phase component and quadrature component zero intermediate frequency signals. According to the orthogonal transformation based on multiphase filtering,.

Be simplified design, to multiphase filtering orthogonal transformation structural drawing 3a, be improved to the structural drawing of Fig. Described step S4 detailed process is as follows:. Utilizing multiphase filter structure to realize that 2D doubly extracts and low-pass filtering, is with 2D road in-phase component I or quadrature component Q, and extraction is 1 tunnel in-phase component or quadrature component.

In the design process of multiphase filter structure, adopt follow-on distributed DA, Distributed Arithmetic algorithm to replace conventional taking advantage of to add structure, to reduce the resource occupation amount. Beneficial effect of the present invention: down conversion method of the present invention, by the parallel processing to signal, obtain the baseband signal of homophase and quadrature, realized the processing to superelevation speed if sampling signal, simultaneously 2 times of extractions in the multiphase filtering orthogonal transformation process have been placed in the follow-up multiphase filter structure, doubly extract with D in the multiphase filtering and to combine, simplify the structure, in addition, in the design process to multiphase filter structure, look-up table is improved, filter coefficient is split, distributed ROM is improved to the combination of distributed ROM and piece ROM, has reduced the resource occupation amount.

The invention will be further elaborated below in conjunction with the drawings and specific embodiments. In the present embodiment, take radar echo signal as example. As shown in Figure 4, concrete steps are as follows:.

Main three parts of method of the present invention form: the parallel processing of image data, intermediate-freuqncy signal down-converted and baseband signal reduction of speed are processed. Wherein, step S1 and step S2 have finished the parallel processing of image data; Step S3 finishes the intermediate-freuqncy signal down-converted; Step S4 finishes the baseband signal reduction of speed and processes.

Detailed process is as follows:. It is MHz that the present invention adopts chirp signal imitation bandwidth, and carrier frequency is the radar echo signal of MHz, and its signal spectrum figure is shown in Fig. According to multiphase filtering orthogonalization, obtain:. And with this moment the data-switching that obtains become the two's complement form to import next stage into. Here, 2 times of extractions originally will carrying out in the multiphase filtering orthogonalization procedure have been placed in the follow-up multiphase filter structure, combine with 2 times of extractions in the multiphase filtering, realize by 4 times of extractions.

Can learn signal spectrum after the multiphase filtering orthogonalization by Fig. For realizing 4 times of extractions, the multiphase filter structure that the present invention adopts, its functional schematic is as shown in Figure 6. Regardless of the end application, whether it is communications, aerospace and defense, or instrumentation, the frequencies of interest are pushing higher into the RF and microwave spectrum.

One possible solution to this scenario is to use an increasing number of downconversion stages, such as what is shown in Figure 1. Integrating DDC functionality with an RF ADC eliminates the need for additional analog downconversion stages and allows the spectrum in the RF frequency domain to be directly converted down to baseband for processing.

The capability of the RF ADC to process spectrum in the gigahertz frequency domain alleviates the need to perform potentially multiple downconversions in the analog domain. The ability of the DDC allows for tenability of the spectrum as well as filtering via the decimation filtering, which also provides the advantage of improving the dynamic range within the band increases SNR.

In this example, the AD is operating with an input clock of First, it is important to understand the setup for the digital processing blocks in the AD The AD will be set to use the digital downconverter DDC where the input is real, the output is complex, the numerically controlled oscillator NCO tuning frequency is set to 98 MHz, half-band filter 1 HB1 is enabled, and the 6 dB gain is enabled.

Since the output is complex, the complex to real conversion block is disabled. The basic diagram for the DDC is shown in Figure 3. In order to understand how the input tones are processed, it is important to understand that the signal first passes through the NCO, which shifts the input tones in frequency, then passes through the decimation, optionally through the gain block, and then optionally through the complex to real conversion.

It is important to understand the macro view of the signal flow through the AD as well. This is illustrated by the block diagram of the AD shown in Figure 4. With an input sample clock of The second harmonic of the input frequency will alias into the first Nyquist zone at This is illustrated by the plot of the Frequency Folding Tool in Figure 5.

The first processing block that the signal passes through in the AD is the NCO that will shift the spectrum to the left in the frequency domain by 98 MHz recall our tuning frequency is 98 MHz.

This will shift the analog input from What is interesting is that we see an unexplained tone in the FFT. However, is this tone really unexplained? The NCO is not subjective and shifts all frequencies. In this case, it has shifted the alias of the fundamental input tone 98 MHz down to 0.