參數(shù)資料
型號: PCM1720
英文描述: Stereo Audio DIGITAL-TO-ANALOG CONVERTER MPEG2/AC-3 COMPATIBLE
中文描述: 立體聲音頻數(shù)字模擬轉(zhuǎn)換器MPEG2/AC-3兼容
文件頁數(shù): 11/13頁
文件大?。?/td> 194K
代理商: PCM1720
PCM1720
11
APPLICATION
CONSIDERATIONS
DELAY TIME
There is a finite delay time in delta-sigma converters. In A/D
converters, this is commonly referred to as latency. For a
delta-sigma D/A converter, delay time is determined by the
order number of the FIR filter stage, and the chosen sampling
rate. The following equation expresses the delay time of
PCM1720:
T
D
= 11.125 x 1/f
S
For f
S
= 44.1kHz, T
D
= 11.125/44.1kHz = 251.4
μ
s
Applications using data from a disc or tape source, such as
CD audio, CD-Interactive, Video CD, DAT, Minidisc,
etc., generally are not affected by delay time. For some
professional applications such as broadcast audio for stu-
dios, it is important for total delay time to be less than 2ms.
OUTPUT FILTERING
For testing purposes all dynamic tests are done on the
PCM1720 using a 20kHz low pass filter. This filter limits
the measured bandwidth for THD+N, etc. to 20kHz. Failure
to use such a filter will result in higher THD+N and lower
SNR and Dynamic Range readings than are found in the
specifications. The low pass filter removes out of band
noise. Although it is not audible, it may affect dynamic
specification numbers.
The performance of the internal low pass filter from DC to
24kHz is shown in Figure 7. The higher frequency rolloff of
the filter is shown in Figure 8. If the user’s application has
the PCM1720 driving a wideband amplifier, it is recom-
mended to use an external low pass filter. A simple 3rd-
order filter is shown in Figure 9. For some applications, a
passive RC filter or 2nd-order filter may be adequate.
FIGURE 8. Low Pass Filter Wideband Frequency Response.
1.0
0.5
0
–0.5
–1.0
d
20
Frequency (Hz)
100
1k
10k
24k
INTERNAL ANALOG FILTER FREQUENCY RESPONSE
(20Hz~24kHz, Expanded Scale)
FIGURE 7. Low Pass Filter Frequency Response.
10
5
0
–5
–10
–15
–20
–25
–30
–35
–40
–45
–50
–55
–60
10
100
1k
10k
100k
1M
10M
Frequency (Hz)
d
INTERNAL ANALOG FILTER FREQUENCY RESPONSE
(10Hz~10MHz)
10k
10k
680pF
10k
1500pF
100pF
+
V
SIN
90
0
–90
–180
–270
–360
100
1k
10k
100k
1M
GAIN vs FREQUENCY
Frequency (Hz)
P
6
–14
–34
–54
–74
–94
G
Gain
Phase
OPA604
FIGURE 9. 3rd-Order LPF.
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