AD1849K Analog Devices, AD1849K Datasheet - Page 22

• Manufacturer Part Number: AD1849K
• Description: Serial-Port 16-Bit SoundPort Stereo Codec
• Manufacturer: Analog Devices

AD1849K
A circuit for 2 V rms line-level inputs is shown in Figure 11.
Note that this is approximately a divide-by-two resistive divider.
An external passive antialias filter is required. If line-level inputs
are already at the 1 V rms levels expected by the AD1849K, the
resistors in parallel with the 560 pF capacitors should be
omitted and the series 5.1 k resistor should be decreased to
2.5 k .
The AD1849K Codec contains a bypassable +20 dB gain block
to accommodate condenser microphones. Particular system
requirements will depend upon the characteristics of the
intended microphone. Figure 12 illustrates one example of how
an electret condenser mike requiring phantom power could be
connected to the AD1849K. CMOUT is shown buffered by an
op amp; a transistor like a 2N4124 will also work fine for this
purpose. Note that if a battery-powered microphone is used, the
buffer and R2s are not needed. The values of R1, R2, and C
should be chosen in light of the mic characteristics and intended
gain. Typical values for these might be R1 = 20 k , R2 = 2 k ,
and C = 220 pF.
Figure 12. AD1849K “Phantom-Powered” Microphone
Input Circuit
LEFT ELECTRET
RIGHT ELECTRET
MICROPHONE
Figure 11. AD1849K 2 V rms Line-Level Input Circuit
CONDENSER
MICROPHONE
CONDENSER
INPUT
INPUT
5.1k
R
R
5.1k
2
2
560pF
560pF
NPO
NPO
1 F
1 F
5k
5k
1/2 SSM-2135
5.1k
OR AD820
5.1k
0.33 F
0.33 F
R
R
C
C
1
1
1/2 SSM-2135
1/2 SSM-2135
OR AD820
OR AD820
LINL
LINR
0.33 F
0.33 F
CMOUT
MINL
MINR
CMOUT
–22–
Figure 13 shows ac-coupled line outputs. The resistors are used
to center the output signals around analog ground. If dc-
coupling is desired, CMOUT could be used with op amps as
mentioned below.
A circuit for headphone drive is illustrated in Figure 14. Drive is
supplied by +5 V operational amps. The circuit shown ac
couples the headphones to the line output.
The AD1849K has a common return path LOUT1C which is
biased up to the CMOUT voltage, nominally 2.25 V. The
AD1849K allows for 6 dB larger output voltage swings by
resetting the OLB bit (Bit 59 of the Control Word) to “0.”
Figure 15 illustrates an alternative headphone connection for
the AD1849K which uses the LOUT1C pin to eliminate the
need for ac coupling. The 12
variations caused by different headphone impedances.
LOUT1L, LOUT1R and LOUT1C are short-circuit protected.
Note that driving headphones directly as shown in Figure 15
with OLB = 0 will cause clipping for large input signals and will
only work with very efficient “Walkman-type” headphones. For
high quality headphone listening, Analog Devices recommends
the circuit shown in Figure 14 with OLB = 1.
Figure 14. AD1849K Headphone Drive Connections
LOUT1C
LOUT1R
LOUT1L
LOUT1C
Figure 13. AD1849K Line Output Connections
LOUT1R
LOUT1L
Figure 15. AD1849K Optional Headphone Drive
Connections
LOUT0L
LOUT0R
10k
10k
12 1/2W
12 1/2W
SSM-2135
1 F
1 F
8.66k
8.66k
resistors minimize output level
47k
47k
470 F
470 F
HEADPHONE
LEFT
HEADPHONE
RIGHT
HEADPHONE
RETURN
HEADPHONE
LEFT
HEADPHONE
RIGHT
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