Analog Devices AD73322L a Datasheet
Low Cost, Low Power CMOS
General-Purpose Dual Analog Front End
FEATURES
Two 16-bit A/D converters
Two 16-bit D/A converters
Programmable input/output sample rates
78 dB ADC SNR
78 dB DAC SNR
64 kHz maximum sample rate
−90 dB crosstalk
Low group delay (25 µs typ per ADC channel, 50 µs typ per
DAC channel)
Programmable input/output gain
Flexible serial port allows up to 4 dual codecs to be
connected in cascade, giving 8 I/O channels
Single-supply operation (2.7 V to 3.3 V)
50 mW typ power consumption at 3.0 V
Temperature range: −40°C to +105°C
On-chip reference
28-lead SOIC, TSSOP, and 44-lead LQFP packages
APPLICATIONS
General-purpose analog I/O
Speech processing
Cordless and personal communications
Te le p ho ny
Active control of sound and vibration
Data communications
Wireless local loop
GENERAL DESCRIPTION
The AD73322L is a dual front-end processor for generalpurpose applications, including speech and telephony. It
features two 16-bit A/D conversion channels and two 16-bit
D/A conversion channels. Each channel provides 78 dB signalto-noise ratio over a voice-band signal bandwidth. It also
features an input-to-output gain network in both the analog
and digital domains. This is featured on both codecs and can
be used for impedance matching or scaling when interfacing to
subscriber line interface circuits (SLICs).
The AD73322L is particularly suitable for a variety of applications in the speech and telephony area, including low bit rate,
high quality compression, speech enhancement, recognition,
and synthesis. The low group delay characteristic of the part
makes it suitable for single or multichannel active control
applications.
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
AD73322L
FUNCTIONAL BLOCK DIAGRAM
AVDD1 AVDD2 DVDD
VFBP1
VINP1
VINN1
VFBN1
VOUTP1
VOUTN1
REFOUT
REFCAP
VFBP2
VINP2
VINN2
VFBN2
VOUTP2
VOUTN2
ADC CHANNEL 1
DAC CHANNEL 1
REFERENCE
ADC CHANNEL 2
DAC CHANNEL 2
AGND1 AGND2 DGND
Figure 1.
The A/D and D/A conversion channels feature programmable
input/output gains with ranges of 38 dB and 21 dB, respectively.
An on-chip reference voltage allows single-supply operation.
The sampling rate of the codecs is programmable with four
separate settings offering 64 kHz, 32 kHz, 16 kHz, and 8 kHz
sampling rates (from a master clock of 16.384 MHz).
A serial port (SPORT) allows easy interfacing of single or
cascaded devices to industry-standard DSP engines. The
SPORT transfer rate is programmable to allow interfacing to
both fast and slow DSP engines.
The AD73322L is available in 28-lead SOIC, 28-lead TSSOP,
and 44-lead LQFP packages.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved.
www.analog.com
AD73322L
SPORT
SDI
SDIFS
SCLK
SE
RESET
MCLK
SDOFS
SDO
00691-001
AD73322L
TABLE OF CONTENTS
Specifications..................................................................................... 4
Sample Rate Divider................................................................... 19
Current Summary......................................................................... 6
Signal Ranges ................................................................................ 7
Timing Characteristics ................................................................ 7
Timing Diagrams.......................................................................... 8
Absolute Maximum Ratings............................................................ 9
ESD Caution.................................................................................. 9
Pin Configurations and Function Descriptions .........................10
Te r mi n ol o g y .................................................................................... 12
Abbreviations .............................................................................. 12
Typical Performance Characteristics and Functional Block
Diagram
Functional Descriptions ................................................................ 14
........................................................................................... 13
Encoder Channels ...................................................................... 14
Programmable Gain Amplifier................................................. 14
ADC ............................................................................................. 14
Analog Sigma-Delta Modulator ............................................... 14
Decimation Filter........................................................................ 15
ADC Coding ............................................................................... 15
Decoder Channel........................................................................ 16
DAC Coding................................................................................ 16
Interpolation Filter ..................................................................... 16
Analog Smoothing Filter and PGA.......................................... 16
Differential Output Amplifiers................................................. 16
Volt a ge R e fere n ce ....................................................................... 16
Analog and Digital Gain Taps................................................... 17
Digital Gain Tap.......................................................................... 18
Serial Port (SPORT)................................................................... 18
SPORT Overview........................................................................ 18
SPORT Register Maps................................................................ 19
Master Clock Divider ................................................................. 19
Serial Clock Rate Divider .......................................................... 19
DAC Advance Register .............................................................. 20
Control Register A ..................................................................... 21
Control Register B...................................................................... 21
Control Register C...................................................................... 21
Control Register D ..................................................................... 22
Control Register E...................................................................... 22
Control Register F...................................................................... 22
Control Register G ..................................................................... 23
Control Register H..................................................................... 23
Operation......................................................................................... 24
Resetting the AD73322L ........................................................... 24
Power Management ................................................................... 24
Operating Modes........................................................................ 24
Program (Control) Mode.......................................................... 24
Data Mode................................................................................... 25
Mixed Program/Data Mode...................................................... 25
Digital Loop-Back Mode ........................................................... 25
SPORT Loop-Back Mode.......................................................... 25
Analog Loop-Back Mode .......................................................... 26
Interfacing ....................................................................................... 27
Cascade Operation..................................................................... 27
Performance .................................................................................... 29
Encoder Section.......................................................................... 29
Encoder Group Delay ................................................................ 30
Decoder Section ......................................................................... 30
On-Chip Filtering....................................................................... 31
Decoder Group Delay................................................................ 31
Design Considerations................................................................... 32
Analog Inputs ............................................................................. 32
Interfacing to an Electret Microphone .................................... 34
Rev. A | Page 2 of 48
AD73322L
Analog Output.............................................................................34
Mixed-Mode Operation.............................................................37
Differential-to-Single-Ended Output.......................................35
Digital Interfacing.......................................................................35
Cascade Operation......................................................................35
Grounding and Layout...............................................................36
DSP Programming Considerations ..............................................37
DSP SPORT Configuration .......................................................37
DSP SPORT Interrupts...............................................................37
DSP Software Considerations When Interfacing to the
AD73322L
Operating Mode ..........................................................................37
....................................................................................37
REVISION HISTORY
12/04—Rev. 0 to Rev. A
Updated Format.................................................................. Universal
Updated Outline Dimensions........................................................46
Changes to Ordering Guide...........................................................47
4/01—Revision 0: Initial Version
Interrupts .....................................................................................37
Initialization.................................................................................38
Running the AD73322L with ADCs or DACs in Power-Down
.......................................................................................................38
DAC Timing Control Example .....................................................40
Configuring an AD73322L to Operate in Data Mode...............41
Configuring an AD73322L to Operate in Mixed Mode ............43
Outline Dimensions........................................................................46
Ordering Guide...........................................................................47
Rev. A | Page 3 of 48
AD73322L
SPECIFICATIONS
AVDD = 3 V ± 10%; DVDD = 3 V ± 10%; DGND = AGND = 0 V, f
unless otherwise noted.
Operating temperature range as follows: A grade, T
= −40°C, T
MIN
Table 1.
A and Y Versions
Parameter Min Typ Max Unit Test Conditions/Comments
REFERENCE
REFCAP
Absolute Voltage, VREFCAP 1.08 1.2 1.32 V
REFCAP TC 50 ppm/°C 0.1 µF capacitor required from REFCAP to AGND2
REFOUT
Typical Output Impedance 130 Ω
Absolute Voltage, V
REFOUT
1.08 1.2 1.32 V Unloaded
Minimum Load Resistance 1 kΩ
Maximum Load Capacitance 100 pF
INPUT AMPLIFIER
Offset ±1.0 mV
Maximum Output Swing 1.578 V Max output swing = (1.578/1.2) × VREFCAP
Feedback Resistance 50 kΩ fC = 32 kHz
Feedback Capacitance 100 pF
ANALOG GAIN TAP
Gain at Maximum Setting +1
Gain at Minimum Setting −1
Gain Resolution 5 Bits Gain step size = 0.0625
Gain Accuracy ±1.0 % Output unloaded
Settling Time 1.0 µs
Delay 0.5 µs
ADC SPECIFICATIONS DAC unloaded
Maximum Input Range at VIN
1, 2
1.578 V p-p Measured differentially
−2.85 dBm Max input = (1.578/1.2) × VREFCAP
Nominal Reference Level at VIN 1.0954 V p-p Measured differentially
(0 dBm0) −6.02 dBm
Absolute Gain
PGA = 0 dB −2.0 −0.7 +0.5 dB 1.0 kHz, 0 dBm0
Gain Tracking Error ±0.1 dB 1.0 kHz, +3 dBm0 to −50 dBm0
Signal-to-Noise and Distortion Refer to Figure 9
PGA = 0 dB 70 78 dB 300 Hz to 3400 Hz; f
79 dB 300 Hz to 3400 Hz; f
77.5 dB 0 Hz to f
Total Harmonic Distortion
PGA = 0 dB −86 −75 dB 300 Hz to 3400 Hz; f
Intermodulation Distortion −61 dB PGA = 0 dB
Idle Channel Noise Crosstalk −72 dBm0 PGA = 0 dB
ADC-to-DAC −107 dB ADC input signal level: 1.0 kHz, 0 dBm0
DAC input at idle
ADC-to-ADC −92 dB ADC1 input signal level: 1.0 kHz, 0 dBm0
ADC2 input at idle; input amplifiers bypassed
−93 dB Input amplifiers included in input channel
DC Offset −20 0 +20 mV PGA = 0 dB
Power Supply Rejection Ratio −65 dB
= 16.384 MHz, f
DMCLK
= +85°C; Y grade, T
MAX
= 8 kHz; TA = T
SAMP
= −40°C, T
MIN
MAX
to T
MIN
= +105°C.
MAX
,
Tap gain change of −FS to +FS
= 8 kHz, PUIA = 0
SAMP
= 8 kHz, PUIA = 1
SAMP
/2; f
SAMP
= 8 kHz
= 8 kHz
SAMP
SAMP
Input signal level at AVDD and DVDD pins:
1.0 kHz, 100 mV p-p sine wave
Rev. A | Page 4 of 48
AD73322L
A and Y Versions
Parameter Min Typ Max Unit Test Conditions/Comments
Group Delay
Input Resistance at PGA
DIGITAL GAIN TAP
Gain at Maximum Setting 1
Gain at Minimum Setting −1
Gain Resolution 16 Bits Tested to 5 MSB of settings
Delay 25 µs Includes DAC delay
Settling Time 100 µs
DAC SPECIFICATIONS DAC unloaded
Maximum Voltage Output Swing
Single-Ended 1.578 V p-p PGA = 6 dB
−2.85 dBm Max output = (1.578/1.2) × VREFCAP
Differential 3.156 V p-p PGA = 6 dB
3.17 dBm Max output = 2 × (1.578/1.2) × VREFCAP
Nominal Voltage Output Swing (0 dBm0)
Single-Ended 1.0954 V p-p PGA = 6 dB
−6.02 dBm
Differential 2.1909 V p-p PGA = 6 dB
0 dBm
Output Bias Voltage 1.2 V REFOUT unloaded
Absolute Gain −1.75 −0.6 +0.75 dB 1.0 kHz, 0 dBm0; unloaded
Gain Tracking Error ±0.1 dB 1.0 kHz, +3 dBm0 to −50 dBm0
Signal-to-Noise and Distortion at 0 dBm0 Refer to Figure 10
PGA = 0 dB 72 78.5 dB 300 Hz to 3400 Hz; f
Total Harmonic Distortion at 0 dBm0
PGA = 0 dB −89 −75 dB 300 Hz to 3400 Hz; f
Intermodulation Distortion −77 dB PGA = 0 dB
Idle Channel Noise Crosstalk −81 dBm0 PGA = 0 dB
DAC-to-ADC −73 dB
−74 dB Input amplifiers included in input channel
DAC-to-DAC −102 dB
Power Supply Rejection −65 dB
Group Delay
50 µs
Output DC Offset
Minimum Load Resistance, R
Single-Ended
Differential 150 Ω
Maximum Load Capacitance, C
Single-Ended 500 pF
Differential 100 pF
FREQUENCY RESPONSE
(ADC and DAC)8 Typical Output
Frequency (Normalized to FS)
0 0 dB
0.03125 −0.1 dB
3, 4
1, 3, 5
25 µs
20 kΩ Input amplifiers bypassed
Tap gain change from −FS to +FS; includes
DAC settling time
1
SAMP
SAMP
= 8 kHz
= 8 kHz
ADC input signal level: AGND;
DAC output signal level: 1.0 kHz, 0 dBm0
Input amplifiers bypassed
DAC1 output signal level: AGND; DAC2
Output signal level: 1.0 kHz, 0 dBm0
Input signal level at AVDD and DVDD pins:
1.0 kHz, 100 mV p-p sine wave
3, 4
1, 6
1, 7
3
L
1, 7
L
25 µs Interpolator bypassed
−50 +5 +60 mV
150 Ω
Rev. A | Page 5 of 48
AD73322L
A and Y Versions
Parameter Min Typ Max Unit Test Conditions/Comments
0.0625 −0.25 dB
0.125 −0.6 dB
0.1875 −1.4 dB
0.25 −2.8 dB
0.3125 − 4.5 dB
0.375 −7.0 dB
0.4375 −9.5 dB
> 0.5 <−12.5 dB
LOGIC INPUTS
V
, Input High Voltage
INH
V
, Input Low Voltage 0 0.8 V
INL
DVDD − 0.8
IIH, Input Current −10 +10 µA
CIN, Input Capacitance 10 pF
LOGIC OUTPUT
VOH, Output High Voltage
DVDD − 0.4
VOL, Output Low Voltage 0 0.4 V |IOUT| ≤100 µA
Three-State Leakage Current −10 +10 µA
POWER SUPPLIES
AVDD1, AVDD2 2.7 3.3 V
2.7 3.3 V
DVDD I
9
DD
See Table 2
1
Test conditions: input PGA set for 0 dB gain, output PGA set for 6 dB gain, no load on analog outputs (unless otherwise noted).
2
At input to sigma-delta modulator of ADC.
3
Guaranteed by design.
4
Overall group delay is affected by the sample rate and the external digital filtering.
5
The ADC’s input impedance is inversely proportional to DMCLK and is approximated by (3/3 × 1011)/DMCLK.
6
Between VOUTP1 and VOUTN1 or between VOUTP2 and VOUTN2.
7
At VOUT output.
8
Frequency responses of ADC and DAC measured with input at audio reference level (the input level that produces an output level of −10 dBm0), with 38 dB
preamplifier bypassed and input gain of 0 dB.
9
Test conditions: no load on digital inputs, analog inputs ac-coupled to ground, no load on analog outputs.
DVDD V
DVDD V |IOUT| ≤100 µA
CURRENT SUMMARY
AVDD = DVDD = 3.3 V. These values are in mA and are typical values unless otherwise noted.
Table 2.
Analog
Conditions
Current
ADCs on only 3.4 6.3 9.7 12 1 YES REFOUT disabled
DACs on only 8.8 6.5 15.3 20 1 YES REFOUT disabled
ADCs and DACs on 11.6 7.0 18.6 23 1 YES REFOUT disabled
ADCs and DACs and
13.8 7.0 20.8 26 1 YES REFOUT disabled
Input amps on
ADCs and DACs and
13.2 7.0 20.2 26 1 YES REFOUT disabled
AGT on
All sections on 17.2 7.0 24.2 31 1 YES
REFCAP on only 0.65 0 0.67 1.25 0 NO REFOUT disabled
REFCAP and REFOUT
2.56 0 2.57 4.5 0 NO
On only
All sections off 0 1.25 1.25 1.8 0 YES
All sections off 0 µA 12.5 µA 12.7 µA 40 µA 0 NO
Digital
Current
Total
Current (Typ)
Rev. A | Page 6 of 48
Total
Current (Max)
SE MCLK ON Comments
MCLK active levels equal
to 0 V and DVDD
Digital inputs static and
Equal to 0 V or DVDD
AD73322L
SIGNAL RANGES
Table 3.
Mnemoic Description Range
VREFCAP 1.2 V ± 10%
VREFOUT 1.2 V ± 10%
ADC Maximum input range at V
IN
Nominal reference level 1.0954 V p-p
DAC Maximum voltage output swing
Single-Ended 1.578 V p-p
Differential 3.156 V p-p
Nominal voltage output swing
Single-Ended 1.0954 V p-p
Differential 2.1909 V p-p
Output bias voltage VREFOUT
TIMING CHARACTERISTICS
AVDD = 3 V ± 10%; DVDD = 3 V ± 10%; AGND = DGND = 0 V; TA = T
Table 4.
Parameter
Limit at T
= −40°C to +105°C
A
Clock Signals See Figure 2
t
1
t
2
t
3
61 ns min MCLK period
24.4 ns min MCLK width high
24.4 ns min MCLK width low
Serial Port See Figure 4 and Figure 5
t
4
t
5
t
6
t
7
t
8
t
9
t
10
t
11
t
12
t
13
t
1
0.4 × t
1
0.4 × t
1
20 ns min SDI/SDIFS setup before SCLK low
0 ns min SDI/SDIFS hold after SCLK low
10 ns max SDOFS delay from SCLK high
10 ns min SDOFS hold after SCLK high
10 ns min SDO hold after SCLK high
10 ns max SDO delay from SCLK high
30 ns max SCLK delay from MCLK
to T
MlN
Unit Description
ns min SCLK period
ns min SCLK width high
ns min SCLK width low
1.578 V p-p
, unless otherwise noted.
MAX
Rev. A | Page 7 of 48
AD73322L
TIMING DIAGRAMS
t
1
t
2
Figure 2. MCLK Ti ming
t
3
00691-002
TO OUTPUT
PIN
15pF
C
L
100µAI
100µAI
OL
2.1V
OH
00691-003
Figure 3. Load Circuit for Timing Specifications
MCLK
SCLK*
t
1
t
13
* SCLK IS INDIVIDUALLY PROGRAMMABLE
IN FREQUENCY (MCLK/4 SHOWN HERE).
t
2
t
5
t
6
t
4
t
3
00691-004
Figure 4. SCLK Ti ming
SE (I)
SCLK (O)
SDIFS (I)
SDI (I)
SDOFS (O)
SDO (O)
THREESTATE
THREESTATE
THREESTATE
t
7
t
8
t
8
t
7
D15D0D1D14D15
t
9
t
12
t
10
t
11
D15 D2 D1 D0 D14
D15
00691-005
Figure 5. Serial Port (SPORT)
Rev. A | Page 8 of 48
AD73322L
ABSOLUTE MAXIMUM RATINGS
TA = 25°C unless otherwise noted.
Table 5.
Parameters Ratings
AVDD, DVDD to GND −0.3 V to +4.6 V
AGND to DGND −0.3 V to +0.3 V
Digital I/O Voltage to DGND −0.3 V to (DVDD + 0.3 V)
Analog I/O Voltage to AGND −0.3 V to (AVDD + 0.3 V)
Operating Temperature Range
Industrial (A Version) −40°C to +85°C
Extended (Y Version) −40°C to +105°C
Storage Temperature Range −65°C to +150°C
Maximum Junction Temperature 150°C
SOIC, θJA Thermal Impedance 71.4°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) 215°C
Infrared (15 sec) 220°C
LQFP, θJA Thermal Impedance 53.2°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) 215°C
Infrared (15 sec) 220°C
TSSOP, θJA Thermal Impedance 97.9°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) 215°C
Infrared (15 sec) 220°C
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those listed in the operational sections
of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the uman body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Rev. A | Page 9 of 48
AD73322L
2
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
VFBN2
VINP1
1
VFBP1
2
VINN1
3
VFBN1
4
REFOUT
REFCAP
AVDD2
AGND2
DGND
DVDD
RESET
SCLK
MCLK
SDO
5
AD73322L
TOP VIEW
6
(Not to Scale)
7
8
9
10
11
12
13
14
Figure 6. 28-Lead Wide Body
28
27
26
25
24
23
22
21
20
19
18
17
16
15
VINN2
VFBP2
VINP2
VOUTN1
VOUTP1
VOUTN2
VOUTP2
AVDD1
AGND1
SE
SDI
SDIFS
SDOFS
00691-006
1
VINP1
2
VFBP1
3
VINN1
4
VFBN1
REFOUT
REFCAP
5
AD73322L
TOP VIEW
6
7
AVDD2
8
AGND2
9
DGND
10
DVDD
11
RESET
12
SCLK
13
MCLK SDIFS
14
SDO
28
27
26
25
24
23
22
21
20
19
18
17
16
15
Figure 7. 28-Lead Thin Shrink
VFBN2
VINN2
VFBP2
VINP2
VOUTN1
VOUTP1
VOUTN2
VOUTP2
AVDD1
AGND1
SE
SDI
SDOFS
00691-007
AVDD2
AVDD2
AGND2
AGND2
AGND2
AGND2
DGND
DGND
DVDD
1
2
3
4
5
6
7
8
9
10
11
REFOUT
REFCAP
NC = NO CONNECT
VFBN142VINN141VFBP140VINP139NC38VFBN
44NC43
PIN 1
12NC13
14
15
SCLK
RESET
AD73322L
TOP VIEW
(Not to Scale)
16
MCLK
SDO
17NC18
VINN236VFBP235VINP234NC
37
19
20
SDIFS
SDOFS
SDI
21SE22
NC
33
32
31
30
29
28
27
26
25
24
23
NC
VOUTN1
VOUTP1
NC
VOUTN2
VOUTP2
NC
AVDD1
AVDD1
AGND1
AGND1
00691-008
Figure 8. 44-Lead Plastic Thin Quad Flatpack
Table 6. Pin Function Descriptions
Mnemonic Function
VINP1 Analog Input to the inverting input amplifier on Channel 1’s positive input.
VFBP1
Feedback Connection from the output of the inverting amplifier on Channel 1’s positive input. When the input amplifiers are
bypassed, this pin allows direct access to the positive input of Channel 1’s sigma-delta modulator.
VINN1 Analog Input to the inverting input amplifier on Channel 1’s negative input.
VFBN1
Feedback connection from the output of the inverting amplifier on Channel 1’s negative input. When the input amplifiers are
bypassed, this pin allows direct access to the negative input of Channel 1’s sigma-delta modulator.
REFOUT Buffered Reference Output, which has a nominal value of 1.2 V.
REFCAP A bypass capacitor to AGND2 of 0.1 µF is required for the on-chip reference. The capacitor should be fixed to this pin.
AVDD2 Analog Power Supply Connection.
AGND2 Analog Ground/Substrate Connection2.
DGND Digital Ground/Substrate Connection.
DVDD Digital Power Supply Connection.
RESET
Active Low Reset Signal. This input resets the entire chip, resetting the control registers and clearing the digital circuitry.
Rev. A | Page 10 of 48
AD73322L
Mnemonic Function
SCLK
MCLK Master Clock Input. MCLK is driven from an external clock signal.
SDO
SDOFS
SDIFS
SDI
SE
AGND1 Analog Ground/Substrate Connection.
AVDD1 Analog Power Supply Connection.
VOUTP2 Analog Output from the Positive Terminal of Output Channel 2.
VOUTN2 Analog Output from the Negative Terminal of Output Channel 2.
VOUTP1 Analog Output from the Positive Terminal of Output Channel 1.
VOUTN1 Analog Output from the Negative Terminal of Output Channel 1.
VINP2 Analog Input to the inverting input amplifier on Channel 2’s positive input.
VFBP2
VINN2 Analog Input to the inverting input amplifier on Channel 2’s negative input.
VFBN2
Serial Clock Output. This rate determines the serial transfer rate to/from the codec. It is used to clock data or control
information to and from the serial port (SPORT). The frequency of SCLK is equal to the frequency of the master clock (MCLK)
divided by an integer number—this integer number being the product of the external master clock rate divider and the serial
clock rate divider.
Serial Data Output. Both data and control information may be output on this pin and are clocked on the positive edge of
SCLK. SDO is in three-state when no information is being transmitted and when SE is low.
Framing Signal Output for SDO Serial Transfers. The frame sync is one bit wide and is active one SCLK period before the first
bit (MSB) of each output word. SDOFS is referenced to the positive edge of SCLK. SDOFS is in three-state when SE is low.
Framing Signal Input for SDI Serial Transfers. The frame sync is one bit wide and is valid one SCLK period before the first bit
(MSB) of each input word. SDIFS is sampled on the negative edge of SCLK and is ignored when SE is low.
Serial Data Input. Both data and control information may be input on this pin and are clocked on the negative edge of SCLK.
SDI is ignored when SE is low.
SPORT Enable. Asynchronous input enable pin for the SPORT. When SE is set low by the DSP, the output pins of the SPORT are
three-stated and the input pins are ignored. SCLK is also disabled internally in order to decrease power dissipation. When SE is
brought high, the control and data registers of the SPORT are at their original values (before SE was brought low); however,
the timing counters and other internal registers are at their reset values.
Feedback connection from the output of the inverting amplifier on Channel 2’s positive input. When the input amplifiers are
bypassed, this pin allows direct access to the positive input of Channel 2’s sigma-delta modulator.
Feedback connection from the output of the inverting amplifier on Channel 2’s negative input. When the input amplifiers are
bypassed, this pin allows direct access to the negative input of Channel 2’s sigma-delta modulator.
Rev. A | Page 11 of 48
AD73322L
TERMINOLOGY
Absolute Gain
A measure of converter gain for a known signal. Absolute gain
is measured (differentially) with a 1 kHz sine wave at 0 dBm0
for the DAC and with a 1 kHz sine wave at 0 dBm0 for the
ADC. The absolute gain specification is used for gain tracking
error specification.
Sample Rate
The rate at which the ADC updates its output register and the
DAC updates its output from its input register. The sample rate
can be chosen from a list of four that are fixed relative to the
DMCLK. Sample rate is set by programming bits DIR0-1 in
Control Register B of each channel.
Crosstalk
Crosstalk is due to coupling of signals from a given channel to
an adjacent channel. It is defined as the ratio of the amplitude
of the coupled signal to the amplitude of the input signal.
Crosstalk is expressed in dB.
Gain Tracking Error
Measures changes in converter output for different signal levels
relative to an absolute signal level. The absolute signal level is
0 dBm0 (equal to absolute gain) at 1 kHz for the DAC and 0
dBm0 (equal to absolute gain) at 1 kHz for the ADC. Gain
tracking error at 0 dBm0 (ADC) and 0 dBm0 (DAC) is 0 dB
by definition.
Group Delay
The derivative of radian phase with respect to radian frequency,
dø(f)/df. Group delay is a measure
of the average delay of a
system as a function of frequency. A linear system with a
constant group delay has a linear phase response. The deviation
of group delay from a constant indicates the degree of nonlinear
phase response of the system.
Idle Channel Noise
The total signal energy measured at the output of the device
when the input is grounded (measured in the frequency range
300 Hz to 3400 Hz).
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities creates distortion
products at sum and difference frequencies of mfa ± nfb where
m, n = 0, 1, 2, 3, etc. Intermodulation terms are those for which
neither m nor n is equal to zero. For final testing, the secondorder terms include (fa + fb) and (fa − fb), while the third-order
terms include (2fa + fb), (2fa − fb), (fa + 2fb) and (fa − 2fb).
Power Supply Rejection
Measures the susceptibility of a device to noise on the power
supply. Power supply rejection is measured by modulating the
power supply with a sine wave and measuring the noise at the
output (relative to 0 dB).
SNR + THD
Signal-to-noise ratio plus harmonic distortion is the ratio of the
rms value of the measured input signal to the rms sum of all
other spectral components in the frequency range 300 Hz to
3400 Hz, including harmonics but excluding dc.
ABBREVIATIONS
Table 7.
Abbreviation Definition
ADC Analog-to-digital converter.
AFE Analog front end.
AGT Analog gain tap.
ALB Analog loop-back.
BW Bandwidth.
CRx
CRx:n
DAC Digital-to-analog converter.
DGT Digital gain tap.
DLB Digital loop-back.
DMCLK
FS Full scale.
FSLB
PGA Programmable gain amplifier.
SC Switched capacitor.
SLB SPORT loop-back.
SNR Signal-to-noise ratio.
SPORT Serial port.
THD Total harmonic distortion.
VBW Voice bandwidth.
A control register where x is a placeholder for
an alphabetic character (A to H). There are eight
read/write control registers on the AD73322L—
CRA through CRH.
A bit position, where n is a placeholder for a
numeric character (0 to 7), within a control
register, where x is a placeholder for an
alphabetic character (A to E). Position 7
represents the MSB and Position 0 represents
the LSB.
Device (internal) master clock. This is the
internal master clock resulting from the
external master clock (MCLK) being divided by
the on-chip master clock divider.
Frame sync loop-back—where the SDOFS of
the final device in a cascade is connected to the
RFS and TFS of the DSP and the SDIFS of first
device in the cascade. Data input and output
occur simultaneously. In the case of nonFSLB,
SDOFS and SDO are connected to the Rx port of
the DSP while SDIFS and SDI are connected to
the Tx port.
Rev. A | Page 12 of 48
AD73322L
TYPICAL PERFORMANCE CHARACTERISTICS AND FUNCTIONAL BLOCK DIAGRAM
80
70
60
50
40
30
S/(N + D) (dB)
20
10
0
–10
–85 –75 –65 –55 –45 –35 –25 –15 –5
Figure 9. S/N(N = D) vs. V
VIN (dBm0)
(ADC @ 3 V) over Voice Bandwidth
IN
(300 Hz to 3.4 kHz)
VFBN1
VINN1
ANALOG
LOOPBACK
VINP1
VFBP1
V
REF
GAIN
±1
5
3.17
00691-009
INVERT
SINGLE-ENDED
ENABLE
0/38dB
PGA
80
70
60
50
40
30
S/(N + D) (dB)
20
10
0
–10
–85 –75 –65 –55 –45 –35 –25 –15 –5
Figure 10. S/N(N = D) vs. V
VIN (dBm0)
(DAC @ 3 V) over Voice Bandwidth
IN
(300 Hz to 3.4 kHz)
DVDDAVDD2AVDD1
DIGITAL
Σ-∆
MODULATOR
GAIN
±1
DECIMATOR
SDI
SDIFS
SCLK
3.17
5
00691-010
VOUTP1
VOUTN1
REFCAP
REFOUT
VFBN2
VINN2
VINP2
VFBP2
VOUTP2
VOUTN2
+6/15dB
PGA
REFERENCE
CONTINUOUS
TIME
LOW-PASS
FILTER
SWITCHED
CAPACITOR
LOW-PASS
FILTER
1-BIT
DAC
DIGITAL
Σ-∆
MODULATOR
INTER-
POLATOR
SERIAL
I/O
PORT
RESET
MCLK
SE
AD73322L
V
REF
ANALOG
LOOPBACK
+6/–15dB
PGA
GAIN
±1
CONTINUOUS
TIME
LOW-PASS
FILTER
INVERT
SINGLE-ENDED
ENABLE
SWITCHED
CAPACITOR
LOW-PASS
FILTER
AGND1 AGND2 DGND
0/38dB
PGA
1-BIT
DAC
DIGITAL
Σ-∆
MODULATOR
DIGITAL
Σ-∆
MODULATOR
GAIN
±1
DECIMATOR
INTER-
POLATOR
SDO
SDOFS
00691-011
Figure 11. Functional Block Diagram
Rev. A | Page 13 of 48
AD73322L
FUNCTIONAL DESCRIPTIONS
ENCODER CHANNELS
Both encoder channels consist of a pair of inverting op amps
with feedback connections that can be bypassed if required, a
switched capacitor PGA and a sigma-delta analog-to-digital
converter (ADC). An on-board digital filter, which forms part
of the sigma-delta ADC, also performs critical system-level
filtering. Due to the high level of oversampling, the input
antialias requirements are reduced such that a simple singlepole RC stage is sufficient to give adequate attenuation in the
band of interest.
PROGRAMMABLE GAIN AMPLIFIER
Each encoder section’s analog front end comprises a switched
capacitor PGA, which also forms part of the sigma-delta
modulator. The SC sampling frequency is DMCLK/8. The
PGA, whose programmable gain settings are shown in Table 8,
may be used to increase the signal level applied to the ADC
from low output sources such as microphones, and can be
used to avoid placing external amplifiers in the circuit. The
input signal level to the sigma-delta modulator should not
exceed the maximum input voltage permitted.
highest frequency of interest. In the case of the AD73322L, the
initial sampling rate of the sigma-delta modulator is DMCLK/8.
The main effect of oversampling is that the quantization noise is
spread over a very wide bandwidth, up to F
/2 = DMCLK/16
S
(Figure 13). This means that the noise in the band of interest is
much reduced. Another complementary feature of sigma-delta
converters is the use of a technique called noise-shaping. This
technique has the effect of pushing the noise from the band of
interest to an out-of-band position (Figure 14). The combination of these techniques, followed by the application of a
digital filter, sufficiently reduces the noise in band to ensure
good dynamic performance from the part (Figure 15).
BAND
OF
INTEREST
A.
FS/2
DMCLK/16
The PGA gain is set by bits IGS0, IGS1, and IGS2 (CRD:0–2) in
control register D.
Table 8. PGA Settings for the Encoder Channel
IGS2 IGS1 IGS0 Gain (dB)
0 0 0 0
0 0 1 6
0 1 0 12
0 1 1 18
1 0 0 20
1 0 1 26
1 1 0 32
1 1 1 38
ADC
Both ADCs consist of an analog sigma-delta modulator and a
digital antialiasing decimation filter. The sigma-delta modulator
noise-shapes the signal and produces 1-bit samples at a
DMCLK/8 rate. This bit stream, representing the analog input
signal, is input to the antialiasing decimation filter. The
decimation filter reduces the sample rate and increases the
resolution.
ANALOG SIGMA-DELTA MODULATOR
The AD73322L’s input channels employ a sigma-delta
conversion technique, which provides a high resolution 16-bit
output with system filtering being implemented on-chip.
Sigma-delta converters employ a technique known as
oversampling, where the sampling rate is many times the
NOISE SHAPING
BAND
OF
INTEREST
BAND
OF
INTEREST
B.
DIGITAL FILTER
C.
Figure 12. Sigma-Delta Noise Reduction
FS/2
DMCLK/16
FS/2
DMCLK/16
Figure 13 through Figure 16 show the various stages of filtering
that are employed in a typical AD73322L application. Figure 13
shows the transfer function of the external analog antialias
filter. Even though it is a single RC pole, its cutoff frequency
is sufficiently far away from the initial sampling frequency
(DMCLK/8) that it takes care of any signals that could be
aliased by the sampling frequency. This also shows the major
difference between the initial oversampling rate and the bandwidth of interest. In Figure 14, the signal and noise-shaping
responses of the sigma-delta modulator are shown. The
signal response provides further rejection of any high
frequency signals, while the noise-shaping pushes the inherent
quantization noise to an out-of-band position. The detail of
00691-012
Rev. A | Page 14 of 48
AD73322L
Figure 15 shows the response of the digital decimation filter
(sinc-cubed response) with nulls every multiple of DMCLK/256
corresponding to the decimation filter update rate for a 64 kHz
sampling. The nulls of the Sinc3 response correspond with
multiples of the chosen sampling frequency. The final detail in
Figure 16 shows the application of a final antialias filter in the
DSP engine. This has the advantage of being implemented
according to the user’s requirements and available MIPS. The
filtering in Figure 13 through Figure 16 is implemented in the
AD73322L.
Figure 13 to Figure 16 show ADC frequency responses.
FB = 4kHz F
Figure 13. Analog Antialias Filter Transfer Function
SIGNAL TRANSFER FUNCTION
NOISE TRANSFER FUNCTION
SINIT
= DMCLK/8
00691-013
The antialiasing decimation filter is a sinc-cubed digital filter
that reduces the sampling rate from DMCLK/8 to DMCLK/256,
and increases the resolution from a single bit to 15 bits or
greater (depending on chosen sampling rate). Its Z transform is
given as
[(1 − Z
−N
)/(1 − Z−1 )]
3
where N is set by the sampling rate
(N = 32 @ 64 kHz sampling N = 256 @ 8 kHz sampling)
Thus, when the sampling rate is 64 kHz, a minimal group delay
of 25 µs can be achieved.
Word growth in the decimator is determined by the sampling
rate. At 64 kHz sampling, where the oversampling ratio (OSR)
between sigma-delta modulator and decimator output equals
32, there are five bits per stage of the three-stage Sinc3 filter.
Due to symmetry within the sigma-delta modulator, the LSB
is always a zero; therefore, the 16-bit ADC output word has
2 LSBs equal to zero, one due to the sigma-delta symmetry and
the other being a padding zero to make up the 16-bit word. At
lower sampling rates, decimator word growth is greater than the
16-bit sample word, therefore truncation occurs in transferring
the decimator output as the ADC word. For example, at 8 kHz
sampling, word growth reaches 24 bits due to the OSR of 256
between the sigma-delta modulator and decimator output. This
yields 8 bits per stage of the three-stage sinc3 filter.
FB = 4kHz F
SINIT
= DMCLK/8
Figure 14. Analog Sigma-Delta Modulator Transfer Function
FB = 4kHz F
SINTER
= DMCLK/256
Figure 15. Digital Decimator Transfer Function
FB = 4kHz F
SRNAL
= 8kHz F
SINTER
= DMCLK/256
Figure 16. Final Filter (HPF) Transfer Function
DECIMATION FILTER
The digital filter used in the AD73322L carries out two
important functions. First, it removes the out-of-band
quantization noise, which is shaped by the analog modulator
and second, it decimates the high frequency bit stream to a
lower rate, 16-bit word.
00691-014
00691-015
00691-016
ADC CODING
The ADC coding scheme is in twos complement format, as
shown in Figure 17). The output words are formed by the
decimation filter, which grows the word length from the single
bit output of the sigma-delta modulator to a word length of up
to 24 bits (depending on decimation rate chosen), which is the
final output of the ADC block. In data mode this value is truncated to 16 bits for output on the serial data output (SDO) pin.
V
+ (V
ANALOG
INPUT
V
ANALOG
INPUT
REF
V
V
REF
× 0.32875)
REF
V
REF
– (V
× 0.32875)
REF
10...00 00...00 01...11
+ (V
– (V
REF
REF
× 0.6575)
× 0.6575)
10...00 00...00 01...11
REF
REF
Figure 17. ADC Transfer Function
V
INN
V
INP
ADC CODE DIFFERENTIAL
V
INN
V
INP
ADC CODE SINGLE-ENDED
00691-017
Rev. A | Page 15 of 48
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