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ADL5375-15ACPZ-R71 数据表(PDF) 24 Page - Analog Devices |
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ADL5375-15ACPZ-R71 数据表(HTML) 24 Page - Analog Devices |
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24 / 32 page  ADL5375 Rev. 0 | Page 24 of 32 RBIP 50Ω RBIN 50Ω 93 92 21 22 IBBN IBBP AD9779 ADL5375-05 RBQN 50Ω RBQP 50Ω 84 83 9 10 RSLI 100Ω RSLQ 100Ω OUT1_N OUT1_P OUT2_P OUT2_N QBBP QBBN LPI 771.1nH LNI 771.1nH 53.62nF C1I 350.1pF C2I LNQ 771.1nH LPQ 771.1nH 53.62nF C1Q 350.1pF C2Q Figure 60. DAC Modulator Interface with 10 MHz Third-Order, Bessel Filter 1 10 100 –60 –50 –40 –30 –20 –10 0 0 6 12 18 24 30 36 FREQUENCY (MHz) MAGNITUDE GROUP DELAY Figure 61. Frequency Response for DAC Modulator Interface with 10 MHz Third-Orde,r Bessel Filter Driving the ADL5375-15 with a TXDAC The ADL5375-15 requires a 1500 mV dc bias and therefore requires a slightly more complex interface that performs a dc level shift on the baseband signals. It is necessary to level-shift the DAC output from a 500 mV dc bias to the 1500 mV dc bias that the ADL5375-15 requires. Level-shifting can be achieved with either a passive network or an active circuit. A passive network of resistors is shown in Figure 62. In this network, the dc bias of the DAC remains at 500 mV while the input to the ADL5375-15 is 1500 mV. It should be noted that this passive level-shifting network introduces approximately 2 dB of loss in the ac signal. RBIP 45.3Ω RBIN 45.3Ω 93 92 21 22 OUT1_N OUT1_P IBBN IBBP 5V AD9779 ADL5375-15 RLIP 3480Ω RLIN 3480Ω RBQN 45.3Ω RSQP 1kΩ RBQP 45.3Ω 84 83 9 10 OUT2_P OUT2_N QBBP QBBN 5V RLQN 3480Ω RLQP 3480Ω RSQN 1kΩ RSIP 1kΩ RSIN 1kΩ Figure 62. Passive Level-Shifting Network For Biasing ADL5375-15 from TxDAC The active level shifting circuit involves the use of the ADA4938 dual-differential amplifier. This device has a VOCM pin that sets the output dc bias. Through this pin, the output common- mode of the amplifier can be easily set to the requisite 1.5 V for biasing the ADL5375-15 baseband inputs. 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 feed- through from the modulator. Figure 63 shows the interface required to use the auxiliary DACs, which adds four resistors to the interface. RBIP 50Ω RBIN 50Ω 93 90 92 21 22 IBBN IBBP AD9779 ADL5375-05 RBQN 50Ω RBQP 50Ω 84 87 89 83 86 9 10 RSLI 100Ω RSLQ 100Ω OUT1_N AUX1_N AUX2_N OUT1_P AUX1_P OUT2_P AUX2_P OUT2_N QBBP QBBN LPI 771.1nH LNI 771.1nH 53.62nF C1I 350.1pF C2I LNQ 771.1nH LPQ 771.1nH 53.62nF C1Q 350.1pF C2Q 250Ω 500Ω 500Ω 500Ω 500Ω 250Ω 250Ω 250Ω Figure 63. DAC Modulator Interface with Auxiliary DAC Resistors |
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