LINEAR Application Note 99 LT5528 WCDMA ACPR AltCPR Noise Measurementshandbook
Update: 29 September, 2023
ACPR (adjacent channel power ratio), AltCPR (alternate channel power ratio), and noise are important performance metrics for digital communication systems that use, for example, WCDMA (wideband code division multiple access) modulation. ACPR and AltCPR are both measures of spectral regrowth. The power in the WCDMA carrier is measured using a 5MHz measurement bandwidth. For ACPR, the total power in a 3.84MHz bandwidth centered at 5MHz (the carrier spacing) away from the center of the outermost carrier is measured and compared to the carrier power. The result is expressed in dBc. For AltCPR, the procedure is the same, except we center the measurement 10MHz away from the center of the outermost carrier. To measure ACPR and AltCPR, refer to the test setup shown in Figure 2. The DUT (device under test) is the LT5528, which is a high linearity direct I/Q modulator. It accepts WCDMA modulation at the baseband inputs, and generates a WCDMA modulated signal at the RF output. Note that a free running RF generator provides the LO signal. This type of generator is used because of its superior noise performance. This is critical, as a noisy LO signal may corrupt the modulator output, and consequently the ACPR measurement. For the generator shown, the automatic level control must be switched off to avoid degrading its broadband noise floor. Also,
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Publication date: 05 June, 2012
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PDF Link: LINEAR Application Note 99 LT5528 WCDMA ACPR AltCPR Noise Measurementshandbook PDF