ad73422 Analog Devices, Inc., ad73422 Datasheet - Page 32

• Manufacturer Part Number: ad73422
• Description: Dual Low Power Cmos Analog Front End With Dsp Microcomputer
• Manufacturer: Analog Devices, Inc.

AD73422
Cascade Operation
Where it is required to configure extra analog I/O channels to
the existing two channels on the AD73422, it is possible to
cascade up to six more channels (using single channel AD73311
or dual channel AD73322 AFEs) by using the scheme described
in Figure 24. It is necessary, however, to ensure that the timing
of the SE and ARESET signals is synchronized at each device in
the cascade. A simple D-type flip-flop is sufficient to sync each
signal to the master clock AMCLK, as in Figure 23.
Connection of a cascade of devices to a DSP, as shown in Fig-
ure 24, is no more complicated than connecting a single device.
Instead of connecting the SDO and SDOFS to the DSP’s Rx
port, these are now daisy-chained to the SDI and SDIFS of the
next device in the cascade. The SDO and SDOFS of the final
device in the cascade are connected to the DSP section’s Rx
port to complete the cascade. SE and ARESET on all devices
are fed from the signals that were synchronized with the AMCLK
using the circuit as described above. The SCLK from only one
device need be connected to the DSP section’s SCLK input(s)
as all devices will be running at the same SCLK frequency and
phase.
Figure 23. SE and ARESET Sync Circuit for Cascaded
Operation
Figure 22. AD73422 AFE to DSP Connection
TO ARESET
SECTION
CONTROL
CONTROL
AMCLK
DSP
AMCLK
TO SE
DSP
DSP
DT
RFS
FL1
TFS
SCLK
DR
FL0
CLK
CLK
D
D
74HC74
74HC74
1/2
1/2
Q
Q
ARESET
SDOFS
SDIFS
SCLK
SDO
SDI
SE
SE SIGNAL
SYNCHRONIZED
TO AMCLK
ARESET SIGNAL
SYNCHRONIZED
TO AMCLK
AD73422
SECTION
AFE
–32–
Interfacing to the AFE’s Analog Inputs and Outputs
The AFE section of the AD73422 offers a flexible interface for
microphone pickups, line level signals or PSTN line interfaces.
This section will detail some of the configurations that can be
used with the input and output sections.
The AD73422 features both differential inputs and outputs on
each channel to provide optimal performance and avoid common-
mode noise. It is also possible to interface either inputs or out-
puts in single-ended mode. This section details the choice of
input and output configurations and also gives some tips toward
successful configuration of the analog interface sections.
Figure 24. Connection of an AD73322 Cascaded to
AD73422
FL0
ANTIALIAS
SECTION
0.047 F
0.047 F
FILTER
DSP
100
FL1
100
Figure 25. Analog Input (DC-Coupled)
REFOUT
VOUTP1
VOUTN1
REFCAP
D2
0.1 F
D1
TFS
DR
RFS
DT
SCLK
74HC74
VFBN1
VINN1
VINP1
VFBP1
V
REF
Q1
Q2
SDOFS
SDOFS
+6/–15dB
SDIFS
SDIFS
SCLK
SCLK
GAIN
SDO
SDO
PGA
SDI
SDI
1
ADDITIONAL
REFERENCE
SECTION
DEVICE 2
AD73322
DEVICE 1
CODEC
CONTINUOUS
AFE
LOW-PASS
FILTER
TIME
AD73422
AMCLK
SE
ARESET
AMCLK
SE
ARESET
V
REF
0/38dB
PGA
REV. 0