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AD9101SE bảng dữ liệu(PDF) 8 Page - Analog Devices |
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AD9101SE bảng dữ liệu(HTML) 8 Page - Analog Devices |
8 / 12 page AD9101 –8– REV. 0 Deglitcher Many recently announced video-speed digital-to-analog con- verters feature very low glitch impulse. This is the result of de- sign emphasis on spurious free dynamic range (SFDR), a key spec for the emerging direct digital synthesis (DDS) market. These DACs have extremely low spurs and often do not require deglitching. Although their specs are impressive, these DACs may suffer har- monic distortion, especially at higher clock rates. Therefore, a deglitcher using the AD9101 can improve SFDR in some cases. Figure 7 illustrates the block diagram for deglitching an AD9713, 12-bit DAC. SAMPLING AMPLIFIER (AD9101) LOW DISTORTION OUTPUT 12 DAC (AD9713) DDS ACCUMULATOR (AD9955) CLK1 CLK2 CLK3 32 TUNING WORD Figure 7. Deglitcher Block Diagram IF-to-Digital Conversion Traditional receivers with information encoded with in phase (I) and quadrature (Q) signals comprise extensive analog signal processing ahead of the pair of ADCs. This I-Q demodulation in the analog domain requires precise gain and phase matching as well as close matching of the ADCs. This leads to high cost both in materials and labor to attain the desired performance. Digital front end designers have paid the cost for these components because ADCs have limited the dy- namic range at higher signal frequencies. IF BPF DSP I Q NUMERICALLY CONTROLLED OSCILLATOR (NCO) ADC ANALOG INPUT H (z) H (z) 12 AD9101 Figure 9. Direct IF-to-Digital Thus, the final IF signal was mixed with quadrature signals from the final LO. The two resultant baseband signals repre- senting I and Q were digitized by independent converters. IF BPF QUADRATURE DEMODULATOR 90° LOCAL OSC. ADC ADC DSP I Q ANALOG INPUT Figure 8. Traditional l-Q Demodulation This method, shown in block form in Figure 8, relies heavily on accuracy of the phase of the analog I and Q signals applied to the ADCs. As little as 0.5 ° of phase error can reduce system dy- namic range by 6 dB or more. Using the bandwidth and low distortion of the AD9101 greatly simplifies the analog front end and allows signal processing to be done in the digital domain which is more predictable and less susceptible to environmental changes. The simplified front end is illustrated in Figure 9. This configuration removes the burden from the analog section. The AD9101 expands the dynamic range of the ADC into the IF bandwidth, allowing straightforward digital algorithms to de- modulate the I and Q data. |
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