PCM1712 Burr-Brown Corporation, PCM1712 Datasheet - Page 14

• Manufacturer Part Number: PCM1712
• Description: DIGITAL-TO-ANALOG CONVERTER
• Manufacturer: Burr-Brown Corporation

The combined oversampling rate of the delta-sigma modu-
lator and the internal 8-times interpolation filter is 48fs. The
theoretical quantization noise performance of the 5-level
delta-sigma modulator is shown in Figure 11.
FIGURE 11. Quantization Noise Spectrum.
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 PCM1712:
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 profes-
sional applications such as broadcast audio for studios, it is
important for total delay time to be less than 2ms.
INTERNAL RESET
When power is first applied to PCM1712, an automatic
reset function occurs after 64 cycles of LRCIN.
For f
–100
–120
–140
–160
–20
–40
–60
–80
20
0
S
0
= 44.1kHz, T
®
PCM1712
5
THIRD-ORDER
T
D
= 12.625 x 1/fs
D
= 12.625/44.1kHz = 286.28 s
Frequency (kHz)
10
MODULATOR
15
20
25
14
OUTPUT FILTERING
For testing purposes all dynamic tests are done on the
PCM1712 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 12. The higher frequency rolloff
of the filter is shown in Figure 13. If the user’s application
has the PCM1712 driving a wideband amplifier, it is recom-
mended to use an external low pass filter. A simple 3rd-
order filter is shown in Figure 14. For some applications, a
passive RC filter or 2nd-order filter may be adequate.
FIGURE 12. Low Pass Filter Frequency Response.
FIGURE 13. Low Pass Filter Frequency Response.
–0.5
–1.0
–10
–15
–20
–25
–30
–35
–40
–45
–50
–55
–60
1.0
0.5
10
–5
0
5
0
20
10
100
100
(20Hz~24kHz, Expanded Scale)
SIMULATED ANALOG FILTER
SIMULATED ANALOG FILTER
FREQUENCY RESPONSE
FREQUENCY RESPONSE
1k
Frequency (Hz)
Frequency (Hz)
(10Hz~10MHz)
10k
1k
100k
1M
10k
10M
24k