廬
APPLICATION BULLETIN
OUTPUT SPECTRUM AND POST-LPF
DESIGN OF THE PCM1710
By Hajime Kawai (BB-Japan) and Robert Watson (Burr-Brown Corp.)
Mailing Address: PO Box 11400 鈥?Tucson, AZ 85734 鈥?Street Address: 6730 S. Tucson Blvd. 鈥?Tucson, AZ 85706
Tel: (520) 746-1111 鈥?Twx: 910-952-111 鈥?Telex: 066-6491 鈥?FAX (520) 889-1510 鈥?Immediate Product Info: (800) 548-6132
This application provides an analysis of the PCM1710鈥檚
output spectrum and data from actual use. In addition, a
sample design of a post-low-pass filter for the PCM1710 and
test measurements are presented for the user鈥檚 reference.
INTERNAL LOW-PASS FILTER
The PCM1710 incorporates a low-pass filter
28
remove
to
ML
1
LRCIN
Input
Interface
oversampled high-frequency spectrum noise. The equivalent
2
27 MC
DIN
Digital
Mode
circuit of this internal low-pass filter is shown in Figure 1.
Filter
Control
BCKIN
CLKO
XTI
XTO
DGND
V
DD
V
CC
2R
AGND2R
EXT1R
EXT2R
V
OUT
R
AGND1
3
4
5
6
7
8
9
10
11
12
13
14
LPF
CMOS Amp
Left
Low-Pass
Filter-Left
5-Level DAC
Right
5-Level DAC
Left
Noise
Shaper
26
25
24
23
22
21
20
19
18
17
16
15
MD
Timing
Control
RSTB
NC
CKSL
DGND
V
DD
V
CC
2L
AGND2L
EXT1L
EXT2L
V
OUT
L
V
CC
1
Figures 2 and 3 show the frequency response of the filter. As
can be seen in Figure 3, the filter has no suppression effect on
frequencies lower than about 100kHz.
DIGITAL FILTER
The PCM1710 also incorporates a digital filter. The attenua-
tion level of this digital filter is 鈥?2dB in the stop-band, and its
frequency response is shown in Figure 4.
10
5
0
鈥?
鈥?0
鈥?5
鈥?0
鈥?5
鈥?0
鈥?5
鈥?0
鈥?5
鈥?0
鈥?5
鈥?0
10
100
1k
10k
100k
1M
10M
Frequency (Hz)
FIGURE 1. Low-Pass Filter Equivalent Circuit.
FIGURE 3. Low-Pass Filter Frequency Response (10Hz ~
10MHz).
0
鈥?0
1.0
0.5
dB
dB
鈥?0
鈥?0
鈥?0
dB
0
鈥?.5
鈥?00
鈥?20
鈥?.0
20
100
1k
Frequency (Hz)
10k
24k
鈥?40
0
20k
40k
60k
80k
100k 120k 140k 160k 180k
Frequency (Hz)
FIGURE 2. Low-Pass Filter Frequency Response (20Hz ~
24kHz, Enlarged).
漏
FIGURE 4. Frequency Response (Normal Mode, De-Em-
phasis OFF).
AB-102
Printed in U.S.A. November, 1995
1995 Burr-Brown Corporation
1
2
3
4
5
