參數(shù)資料
型號: AD1843JST
廠商: ANALOG DEVICES INC
元件分類: 消費家電
英文描述: Serial-Port 16-Bit SoundComm Codec
中文描述: SPECIALTY CONSUMER CIRCUIT, PQFP100
封裝: PLASTIC, TQFP-100
文件頁數(shù): 56/64頁
文件大?。?/td> 848K
代理商: AD1843JST
REV. 0
–56–
AD1843
“room” in the frequency domain for a second pole, especially in
modem applications, where the signal bandwidth is 4.2 kHz. A
suggested capacitor value is 120 pF when using the 10K op amp
feedback resistor as shown, for a –3 dB point of approximately
133 kHz. Note that the combined effect of both filters causes a
gain error of approximately 0.1% at 4.2 kHz.
1μF
0.9k
LINRN
LINLN
10k
10k
1/2
SSM2135
10k
SOURCE
10k
1/2
SSM2135
1μF
1000pF
NPO
LINLP
LINRP
CLOSE TO SOURCE
CLOSE TO AD1843
1μF
CMBUF
CMBUF
Figure 21. Single-Ended to Differential Converter
The AD1843 Codec contains an optional +20 dB gain block to
accommodate condenser microphones. Particular system re-
quirements will depend upon the characteristics of the intended
microphone. Figure 22 illustrates one example of how an elec-
tret condenser mic requiring phantom power could be con-
nected to the AD1843. CMOUT is shown buffered by an op
amp; the current drawn from CMOUT should be as minimal as
possible. 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 in-
tended gain. Typical values for these might be R1 = 20 k
,
R2 = 2 k
, and C = 220 pF. Figure 22 shows a voltage follower
buffer on the CMOUT signal. The output of this buffer,
CMBUF, can be used in any circuit which needs the common-
mode bias point from the AD1843’s on-chip voltage reference.
The AD820 is a JFET input op amp whose very high imped-
ance inputs present essentially no load on the CMOUT output
from the AD1843.
1/2 SSM2135
OR AD820
5k
1μF
CMOUT
MICL
LEFT ELECTRET
CONDENSER
MICROPHONE
INPUT
RIGHT ELECTRET
CONDENSER
MICROPHONE
INPUT
R1
0.33μF
C
1/2 AD820
R2
R2
1/2 SSM2135
OR AD820
5k
1μF
MICR
R1
0.33μF
C
CMBUF
Figure 22. AD1843 “Phantom-Powered” Microphone
Input Circuit
Connect unused analog inputs to CMBUF or leave them
unconnected; do not connect unused analog inputs to
either analog power or ground!
Figure 23 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 above, if desired.
LOUT1R
LOUT2RP
47k
1μF
LOUT1L
LOUT2LP
47k
1μF
Figure 23. AD1843 (Single-Ended) Line Output
Connections
For optimal performance, the AD1843 DAC2 output has provi-
sion for a differential configuration. A simple differential-to-
single-ended conversion circuit is shown in Figure 24. The
noise rejection of this circuit is limited by the match of the R
i
and R
f
resistors. The resistors should be 1% tolerance compo-
nents. The equation that determines the output voltage is as
follows:
V
O
= (
R
f
/
R
i
)(
V
+) – (
R
f
/
R
i
)(
V
–)
For maximum noise immunity, this circuit should be located in
close proximity to where V
O
is processed. Another differential
receiver option is the SSM2141, which provides better matching
than a discrete implementation.
1/2
SSM2135
R
f
1/2
SSM2135
LOUT2LN
(V–)
10pF
V
O
R
i
R
f
10pF
LOUT2LP
(V+)
CMBUF
R
i
1/2
SSM2135
R
f
1/2
SSM2135
LOUT2RN
(V–)
10pF
V
O
R
i
R
f
10pF
LOUT2RP
(V+)
CMBUF
R
i
Figure 24. AD1843 Differential-to-Single-Ended Converter
Line Output Connections
A circuit for headphone drive is illustrated in Figure 25. The
AD1843 headphone output is designed to drive loads of 32
ohms or smaller (i.e., higher impedance). If larger loads are
used (e.g., 16 ohms or 8 ohms), the analog output will be dis-
torted for large output signals because of current limiting.
“Walkman”-type headphone impedances are generally around
32 ohms. Telephone handset impedances are typically 150 ohms.
HPOUTL
HPOUTR
HPOUTC
Figure 25. AD1843 Headphone Drive Connections
Figure 26 shows an example circuit for the mono output
(MOUT) from the AD1843. The OP279 is a single +5 V supply
op amp which can drive a small 8 ohm or 16 ohm speaker to
modest levels.
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