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ADL5370 Datasheet(PDF) 14 Page - Analog Devices |
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ADL5370 Datasheet(HTML) 14 Page - Analog Devices |
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ADL5370 Rev. 0 | Page 14 of 20 RBIP 50Ω RBIN 50Ω 93 92 19 20 IBBN IBBP AD9779 ADL5370 RBQN 50Ω RBQP 50Ω 84 83 23 24 RSLI 100Ω RSLQ 100Ω OUT1_N OUT1_P OUT2_P OUT2_N QBBP QBBN LPI 2.7nH LNI 2.7nH 1.1nF C1I 1.1nF C2I LNQ 2.7nH LPQ 2.7nH 1.1nF C1Q 1.1nF C2Q Figure 32. DAC Modulator Interface with 3 MHz Third-Order Low-Pass Filter USING THE AD9779 AUXILIARY DAC FOR CARRIER FEEDTHROUGH NULLING The AD9779 features an auxiliary DAC that can be used to inject small currents into the differential outputs for each main DAC channel. This feature can be used to produce the small offset voltages necessary to null out the carrier feedthrough from the modulator. Figure 33 shows the interface required to utilize the auxiliary DACs. This adds four resistors to the interface. RBIP 50Ω RBIN 50Ω 93 90 92 19 20 IBBN IBBP AD9779 ADL5370 RBQN 50Ω RBQP 50Ω 84 87 89 83 86 23 24 RSLI 100Ω RSLQ 100Ω OUT1_N AUX1_N AUX2_N OUT1_P AUX1_P OUT2_P AUX2_P OUT2_N QBBP QBBN LPI 2.7nH LNI 2.7nH 1.1nF C1I 1.1nF C2I LNQ 2.7nH LPQ 2.7nH 1.1nF C1Q 1.1nF C2Q 250Ω 500Ω 500Ω 500Ω 500Ω 250Ω 250Ω 250Ω Figure 33. DAC Modulator Interface with Auxiliary DAC Resistors GSM OPERATION Figure 34 shows the GSM EVM and spectral mask performance vs. output power for the ADL5370 at 450 MHz. For a given LO amplitude, the performance is independent of output power. –35 –56 –49 –42 –63 –70 –77 –84 –91 2.0 1.5 1.0 0.5 0 012345 67 OUTPUT POWER (dBm) 250kHz 400kHz 600kHz EVMRMS (%) EVMPK (%) 1200kHz Figure 34. GSM EVM and Spectral Performance vs. Channel Power at 450 MHz vs. Output Power; LO Power = 0 dBm Figure 35 shows the GSM EVM, spectral mask performance and 6 MHz offset noise vs. LO amplitude at 450 MHz with an output power of 6 dBm. Increasing the LO drive level improves the noise performance but degrades EVM performance. –35 –56 –49 –42 –63 –70 –77 –84 –112 –105 –98 –91 3.1 2.9 2.7 2.5 2.3 2.1 1.9 1.7 1.5 1.3 1.1 0.9 –6 –4 –2 0246 LO AMPLITUDE (dBm) 250kHz 400kHz 600kHz 1200kHz EVMRMS (%) EVMPK (%) 6 MHz OFFSET NOISE Figure 35. GSM EVM, Spectral Performance, and 6 MHz Noise Floor vs. LO Power at 450 MHz; Output Power = 6 dBm Figure 35 illustrates that an LO amplitude of 0 dBm provides the ideal operating point for noise and EVM for a GSM signal at 450 MHz. |
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