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ADP3334 Datasheet(PDF) 3 Page - Analog Devices |
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ADP3334 Datasheet(HTML) 3 Page - Analog Devices |
3 / 5 page Circuit Note CN-0285 Rev. 0 | Page 3 of 5 The ADF4351 output match consists of the ZBIAS pull-up and, to a lesser extent, the decoupling capacitors on the supply node. To get a broadband match, it is recommended to use either a resistive load (ZBIAS = 50 Ω) or a resistive in parallel with a reactive load for ZBIAS. The latter gives slightly higher output power, depending on the inductor chosen. Note that it is possible to place the parallel resistor as a differential component (that is, 100 Ω) in Position C1c to minimize board space (see Filter Type B, Table 2). Design the filter with a cutoff approximately 1.2 times to 1.5 times the highest frequency in the band of interest. This cutoff allows margin in the design, because typically the cutoff is lower than designed due to parasitics. The effect of printed circuit board (PCB) parasitics can be simulated in an electromagnetic (EM) simulation tool for improved accuracy. Figure 3. ADF4351 RF Output Filter Schematic As can be seen from Table 2, at frequencies lower than 1250 MHz, a fifth-order filter is required. For 1.25 GHz to2.8 GHz, third-order filtering is sufficient. For frequencies more than 2.8 GHz, filtering is not required because the harmonic levels are sufficiently low to meet the sideband suppression specifications. Figure 4. Sideband Suppression for Filter Type B, 850 MHz to 2450 MHz Figure 5. EVM Plot A sweep of sideband suppression vs. frequency is shown in Figure 4 for the circuit using Filter Type B (800 MHz to 2400 MHz). In this sweep, the test conditions were the following: • Baseband I/Q amplitude = 1 V p-p differential sine waves in quadrature with a 500 mV (ADL5375-05) dc bias • Baseband I/Q frequency (fBB) = 1 MHz. EVM is a measure of the quality of the performance of a digital transmitter or receiver and is a measure of the deviation of the actual constellation points from their ideal locations, due to both magnitude and phase errors (see Figure 5). EVM measurements are given in Table 3 comparing the results with and without the filter. In this case, the baseband I/Q signals were generated using 3GPP Test Model 4 using a Rohde & Schwarz AMIQ I/Q modulation generator with differential I and Q analog outputs. Filter Type B was also used. A block diagram of the test setup for the EVM is shown in Figure 6. For comparative purposes, the ADF4350 is also measured. Lower EVM due to in-band PLL noise improvements on the ADF4351 can be seen in Table 3. Other contributing factors to the EVM improvement are the lower phase frequency detector (PFD) spurious levels on the ADF4351. ADF4351 12 RFOUTA+ 13 RFOUTA– ADL5375 3 LOIP 4 LOIN L1 L2 1nF L1 L2 1nF C1a C1a C1c C2a C2a C2c C3a C3a C3c ZBIAS ZBIAS 120pF 120pF 0.1µF 3.3V –70 –65 –60 –55 –50 –45 –40 –35 –30 –25 –20 800 1000 1200 1400 1600 1800 2000 2200 2400 CARRIER FREQUENCY (MHz) 5dBm FILTER B: 850MHz TO 2450MHz Q I ERROR VECTOR MEASURED SIGNAL PHASE ERROR (I/Q ERROR PHASE) MAGNITUDE ERROR (I/Q ERROR PHASE) IDEAL SIGNAL (REFERENCE) 0 |
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