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Communication D/A Converter Reconstruction Filter
40
20
0
Power – dB
–20
–40
–60
–80
–100
0 2 4 6 8 10 12 14 16
f – Frequency – MHz
Figure 13–5. QPSK Power Spectral Density Without Raised Cosine Filter — W-CDMA
Amplitude
0 2 MHz 28.7
CLK
30.772
f ( MHz)
Figure 13–6. Reconstruction Filter Characteristics
Figure 13–7 shows a first-order reconstruction (low-pass) filter consisting of a high-speed
differential amplifier configured for unity gain. The DAC outputs are terminated into 50 Ω.
In Figure 13–7, the value for the filter capacitor is given by the expression:
13-14