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AD6676EBZ データシート(PDF) 26 Page - Analog Devices |
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AD6676EBZ データシート(HTML) 26 Page - Analog Devices |
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26 / 90 page  AD6676 Data Sheet Rev. D | Page 26 of 90 –130 –160 –155 –150 –145 –140 –135 200 220 240 260 280 300 320 360 400 340 380 FREQUENCY (MHz) OSR = 10 (BW = 160MHz) OSR = 20 (BW = 80MHz) OSR = 40 (BW = 40MHz) OSR = 80 (BW = 20MHz) Figure 72. NSD vs. Oversampling Ratio (FIF = 300 MHz, FADC = 3.2 GHz, LEXT = 19 nH) –140 –160 –158 –156 –154 –152 –150 –148 –146 –144 –142 –100 –80 –60 –40 –20 0 20 60 100 40 80 NORMALIZED ZERO IF FREQUENCY (MHz) IF = 100MHz WITH LEXT = 100nH IF = 200MHz WITH LEXT = 43nH IF = 300MHz WITH LEXT = 19nH Figure 73. NSD at Pass Band Edge Improvement as FIF Is Increased from 100 MHz to 300 MHz with Fixed Oversampling Ratio = 16 (BW = 100 MHz, FADC = 3.2 GHz) The impact of a uneven NSD profile on a particular application depends on the bandwidth and modulation characteristics of the IF signal being digitized and demodulated. For example, a multimode software defined radio containing narrow-band carriers situated anywhere across the pass band must consider the NSD performance at the highest levels across the pass band because this represents the worst-case NSD when calculating the in-band noise for a narrow-band signal in this region. Conversely, a single wideband QAM signal falling at the center of the IF pass band benefits from excellent in-band noise performance because the NSD remains the lowest in this region. Note that the AD6676 specified NF is measured in the region where its NSD is highest. STF and NTF Repeatability After the application parameters have been determined, the STF and NTF characteristics of the AD6676 remain repeatable and stable over temperature and among devices. The on-chip calibration performed during the power-up initialization phase reduces the device-to-device variation that may otherwise exist due to tolerances associated with the device process or the external inductor, LEXT. It is worth noting that that the small variation in STF and NTF that does exist is likely to be less than traditional receiver solutions employing low oversampling ADCs with aggressive high order LC antialiasing filters. L and C component tolerances as well as variation in active device source and load impedances must be considered in the Monte Carlo analysis. The following application parameters were used to demonstrate STF and NTF repeatability: fCLK = 3.2 GHz, FIF = 250 MHz, BW = 75 MHz, LEXT = 19 nH, IDAC1FS = 4 mA, MRGN = default. Figure 74 and Figure 75 demonstrate the repeatability and temperature stability of the STF and NTF responses of single devices for five consecutive power-up initialization operations in which the device is calibrated at 25°C and then allowed to drift to −40°C and +85°C. 0.2 –1.0 –0.8 –0.6 –0.4 –0.2 0 200 210 220 230 240 250 260 280 300 270 290 FREQUENCY (MHz) TA = –40°C TA = +25°C TA = +85°C Figure 74. STF Variation over Temperature for a Single Device for Five Consecutive Power-Up Initialization Operations –146 –148 –150 –152 –154 –156 –158 –160 200 210 220 230 240 250 260 280 300 270 290 FREQUENCY (MHz) TA = –40°C TA = +25°C TA = +85°C Figure 75. NTF Variation over Temperature for a Single Device for Five Consecutive Power-Up Initialization Operations |
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