AD1847
Miscellaneous
P in Nam e
P LCC
TQFP
I/O
D escription
XT AL1I
XT AL1O
XT AL2I
XT AL2O
XCT L1:O
40
41
42
43
34
35
36
37
I
24.576 MHz Crystal # 1 Input.
24.576 MHz Crystal # 1 Output.
16.9344 MHz Crystal # 2 Input.
16.9344 MHz Crystal # 2 Output.
O
I
O
O
37 & 36 31 & 30
External Control. T hese T T L signals reflect the current status of register bits inside the
AD1847. T hey can be used for signaling or to control external logic.
VREF
16
10
O
Voltage Reference. Nominal 2.25 volt reference available externally as a voltage datum
for dc-coupling and level-shifting. VREF should not have any signal dependent load.
VREFI
15
21
9
I
I
Voltage Reference Internal. Voltage reference filter point for external bypassing only.
L_FILT
15
Left Channel Filter Capacitor. T his pin requires a 1.0 µF capacitor to analog ground
for proper operation.
R_FILT
NC
19
29
13
23
I
Right Channel Filter Capacitor. T his pin requires a 1.0 µF capacitor to analog ground
for proper operation.
No Connect. Do not connect.
P ower Supplies
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P LCC
TQFP
I/O
D escription
VCC
13 & 25
7 & 19
I
I
I
I
Analog Supply Voltage (+5 V).
Analog Ground.
GNDA
VDD
14, 20, 24
2, 9, 34, 39
3, 10, 35, 38
8, 14, 18
40, 3, 28, 33
41, 4, 29, 32
Digital Supply Voltage (+5 V).
Digital Ground.
GNDD
(Continued from page 1)
Analog Mixing
AUX1 and AUX2 analog stereo signals can be mixed in the ana-
log domain with the DAC output. Each channel of each auxil-
iary analog input can be independently gained/attenuated from
+12 dB to –34.5 dB in –1.5 dB steps or completely muted. T he
post-mixed DAC output is available on L_OUT and R_OUT
externally and as an input to the ADCs.
T he ∑∆ DACs are preceded by a digital interpolation filter. An
attenuator provides independent user volume control over each
DAC channel. Nyquist images are removed from the DACs’
analog stereo output by on-chip switched-capacitor and
continuous-time filters. T wo stereo pairs of auxiliary line-level
inputs can also be mixed in the analog domain with the DAC
output.
Even if the AD1847 is not playing back data from its DACs, the
analog mix function can still be active.
T he AD1847 serial data interface uses a T ime Division Multi-
plex (T DM) scheme that is compatible with DSP serial ports
configured in Multi-Channel Mode with 32 16-bit time slots
(i.e., SPORT 0 on the ADSP-2101, ADSP-2115, etc.).
Analog-to-D igital D atapath
T he ∑∆ ADCs incorporate a proprietary fourth-order modula-
tor. A single pole of passive filtering is all that is required for
antialiasing the analog input because of the ADC’s high 64
times oversampling ratio. T he ADCs include digital decimation
filters that low-pass filter the input to 0.4 ϫ FS. (“FS’’ is the
word rate or “sampling frequency.”) ADC input overrange con-
ditions will cause status bits to be set that can be read.
AUD IO FUNCTIO NAL D ESCRIP TIO N
T his section overviews the functionality of the AD1847 and is
intended as a general introduction to the capabilities of the de-
vice. As much as possible, detailed reference information has
been placed in “Control Registers” and other sections. T he user
is not expected to refer repeatedly to this section.
D igital-to-Analog D atapath
T he ∑∆ DACs contain a programmable attenuator and a low-
pass digital interpolation filter. T he anti-imaging interpolation
filter oversamples and digitally filters the higher frequency im-
ages. T he attenuator allows independent control of each DAC
channel from 0 dB to –94.5 dB in 1.5 dB steps plus full mute.
T he DACs’ ∑∆ noise shapers also oversample and convert the
signal to a single-bit stream. T he DAC outputs are then filtered
in the analog domain by a combination of switched-capacitor
and continuous-time filters. T hese filters remove the very high
frequency components of the DAC bitstream output. No exter-
nal components are required.
Analog Inputs
T he AD1847 SoundPort Stereo Codec accepts stereo line-level
inputs. All inputs should be capacitively coupled (ac-coupled) to
the AD1847. LINE1, LINE2, and AUX1, and post-mixed DAC
output analog stereo signals are multiplexed to the internal pro-
grammable gain amplifier (PGA) stage.
T he PGA following the input multiplexer allows independent
selectable gains for each channel from 0 to 22.5 dB in +1.5 dB
steps. T he Codec can operate either in a global stereo mode or
in a global mono mode with left-channel inputs appearing at
both channel outputs.
REV. B
–7–
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