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Gain and Phase Response
5-6
5.4 Gain and Phase Response
The APA100 is a closed−loop, class-D audio power amplifier with an LC output
filter. The output filter and the 39-kHz loop bandwidth limit the bandwidth of the
APA100 reference design. The gain versus frequency curve is shown in
Figure 5−8. The 4-Ω curve rolls off sooner than the 8-Ω curve.
Figure 5−8. APA100 Gain vs Frequency With 4-W and 8-W Load
40
35
30
25
20
15
10
5
0
20 100 200 1 k 2 k 10 k 20 k
Gain − dB
f − Frequency − Hz
4 W
8 W
5.5 Signal-to-Noise Ratio (SNR)
The APA100 has low noise and a wide output swing. The noise does not
increase with output power making the signal-to-noise ratio (SNR) just before
clipping good for this type of amplifier. The noise was measured with an
A-weighted filter to be 350 µV rms. The amplifier can output 19 Vrms. This
makes the SNR 95 dB at 19-Vrms output.