Digital characteristics of high speed number of modes converters

Today's High Speed ​​Mold Converter (DAC) usually contains many digital signal processing modules to make it easier to use. It should be discussed, we use Ti DAC34H84, which is a 4-channel, 16-bit, 1250 msps DAC. The reason for this is that it is a typical high speed digital to analog converter, DAC has isolated input and the FIFO input clock domain, digital interpolation module, a fine frequency resolution digital quadrature modulation, and analog quadrature modulator correction sin (x) / x correction. The paper will describes the function and role of these properties. Be Be FIG 1 DAC34H84 functional configuration of FIG. The first module is a digital interpolation module, which is responsible for increasing the sampling rate of the DAC internal digital signal. In general, increasing step by using double the sampling rate, the interpolation is achieved. By inserting zeros between the input sample points to do the job, which fIF and FIN - generating two signals fIF. A low-pass filter through digital, situated removed FIN - fIF of the second signal, leaving only the signal fIF. The reason for using interpolation and zero-order used to keep the majority of high-speed DAC output structure. Use of zero-order hold, the DAC according to the digital sampling clock cycle initial output amplitude corresponding settings, then hold until the next clock period and until the end of the output sample. This produces an output of a "staircase" type of frequency response as represented by Equation 1: sin (π * fIF / fs) / (? π * fIF / fs) Equation 1 Wherein, fIF analog output frequency, and fs is the sampling rate. This response has a low-pass effect (see Figure 2), which is the loss at f = fs / 2 of ~ 3.5 dB, and is zero at multiples of fs. Although the DAC output signal of the image will be at N * fs +/- fIF, but higher Nyquist amplitude image (the Nyquist) region at much lower than the fIF signal, thus lower signal to noise ratio (SNR) and possibly noticeable decrease in amplitude. This limits put in most applications fs / 2 or less the output signal frequency. Further, the FS signal and fIF - fIF interval between the images, as fIF close fs / 2 is reduced, so that the analog filter at the DAC output (FS role is to remove - unwanted image fIF) is difficult to establish, eventually fIF most applications is limited to fs / 3 or less. Be Be Interpolation module 2 without the DAC output spectrum, Read, technology zone A transcoding error field produces two interference sharing Digital circuit design and analog ground isolation techniques parse Static electricity can cause great harm to the terminals and other electronic components On the basic problem of switching power supply design solutions A combinational logic circuit combining circuit configuration described features

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