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AD8346ARU Fiches technique(PDF) 9 Page - Analog Devices |
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AD8346ARU Fiches technique(HTML) 9 Page - Analog Devices |
9 / 12 page REV. 0 AD8346 –9– AC Coupled Interface An ac coupled interface can also be implemented. This is shown in Figure 24. This has the advantage that there is almost no voltage loss due to the biasing network, allowing the AD8346 inputs to be driven by the full 2 V p-p differential signal from the AD9761 (each of the DAC’s four outputs delivering 1 V p-p). As in the dc coupled case, the bias levels on the I and Q inputs should be set to as precise a level as possible, relative to each other. This prevents the introduction of additional input offset voltages. In the example shown, the bias level on each input is set to approximately 1.2 V. The 2.43 k Ω resistors should have a ratio tolerance of 0.1% or better. "I" DAC 2 LATCH "I" IOUTB IOUTA "Q" DAC 2 LATCH "Q" QOUTB QOUTA MUX CONTROL SELECT WRITE CLOCK AD9761 DVDD DCOM AVDD 0.1 F RSET 2k SLEEP FS ADJ REFIO DAC DATA INPUTS CFILTER 100 100 CFILTER 100 100 500 500 500 500 500 500 500 500 0.1 F 634 +5V PHASE SPLITTER VOUT IBBP IBBN QBBP QBBN AD8346 LOIP LOIN VPS1 VPS2 0.5V p-p EACH PIN WITH VCM = 1.2V +5V Figure 23. AD8346 Interface to AD9761 TxDAC 2 LATCH "I" IOUTB IOUTA 2 LATCH "Q" QOUTB QOUTA MUX CONTROL SELECT WRITE CLOCK AD9761 DVDD DCOM AVDD 0.1 F RSET 2k SLEEP FS ADJ REFIO DAC DATA INPUTS CFILTER 100 100 CFILTER 100 100 0.1 F 1k +5V PHASE SPLITTER VOUT IBBP IBBN QBBP QBBN AD8346 LOIP LOIN VPS1 VPS2 1V p-p EACH PIN WITH VCM = 1.2V +5V 0.01 F 0.01 F 0.01 F 0.01 F "I" DAC 2.43k 2.43k 2.43k 2.43k 2.43k 2.43k 2.43k 2.43k "Q" DAC Figure 24. AC-Coupled DAC Interface The network shown has a high-pass corner frequency of approximately 14.3 kHz (note that the 12 k Ω input imped- ance of the AD8346 has been factored into this calcula- tion). Increasing the resistors in the network or increasing the coupling capacitance will reduce the corner frequency further. Note that the LO suppression can be manually optimized by replacing a portion of the four “top” 2.43 k Ω resistors with potentiometers. In this case, the “bottom” four resis- tors in the biasing network would no longer need to be precision devices. |
Numéro de pièce similaire - AD8346ARU |
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Description similaire - AD8346ARU |
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