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Analog Gain by Balanced Amplifier
REFERENCE CURRENT RESISTOR
APPLICATION FOR EXTERNAL DIGITAL FILTER INTERFACE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
WDCK(WordClock)
DATA-L
BCK
SCK
DATA-R
DF1704
DF1706
PMD200
Mode
Control
RST
ZEROL
ZEROR
WDCK(LRCK)
DATAL (DATA)
BCK
SCKI
DGND
V
DD
SCKO
MDO
MDI
MC
CS
V 3
CC
AGND2
I
OUT
L–
I
OUT
L+
V
CC
2
V
CC
1
V
COM
3
I
REF
V
COM
2
V
COM
1
AGND1
I
OUT
R+
I
OUT
R–
DATAR(MUTE)
Analog
OutputStage
SameasStandard
Application
B0201-01
():OriginalPinName
APPLICATIONS FOR INTERFACING WITH THE EXTERNAL DIGITAL FILTER
PCM1738
SBAS174C – FEBRUARY 2002 – REVISED FEBRUARY 2007
The I/V converters are followed by balanced amplifier stages that sum the differential signals for each channel,
creating a single-ended voltage output. In addition, the balanced amplifiers provide a second-order, low-pass
filter function that band-limits the audio output signal. The cutoff frequency and gain is given by external R and C
component values. In the case of Figure 40 , the cutoff frequency is 45 kHz with a gain of 1. The output voltage
for each channel is 6.2 Vp-p, or 2.2 Vrms.
As shown in the analog output application circuit, marked R
1
on Figure 40 , there is a resistor connected from
I
REF
(pin 21) to the analog ground, designated as R
1
. This resistor sets the current for the internal reference
circuit. The value of R
1
must be 16 k Ω , ± 1% in order to match the specified gain error shown in the Electrical
Characteristics table.
Figure 41. Connection Diagram for External Digital Filter (Internal DF Bypass Mode) Application
For some applications, it may be desirable to use an external digital filter to perform the interpolation function, as
it may provide improved stop-band attenuation or other special features not available with the PCM1738's
internal digital filter.
The PCM1738 supports the use of an external digital filter, including:
• The DF1704 and DF1706 from Texas Instruments
• Pacific Microsonics PMD100 HDCD filter/decoder ICs
• Programmable digital signal processors
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