4 ADC/8 DAC with PLL,
192 kHz, 24-Bit Codec
AD1938
Data Sheet
FEATURES
GENERAL DESCRIPTION
PLL generated or direct master clock
Low EMI design
108 dB DAC/107 dB ADC dynamic range and SNR
−94 dB THD + N
3.3 V single supply
Tolerance for 5 V logic inputs
Supports 24 bits and 8 kHz to 192 kHz sample rates
Differential ADC input
Single-ended DAC output
Log volume control with autoramp function
SPI controllable for flexibility
Software-controllable clickless mute
Software power-down
Right-justified, left-justified, I2S-justified, and TDM modes
Master and slave modes up to 16-channel input/output
48-lead LQFP package
Qualified for automotive applications
The AD1938 is a high performance, single-chip codec that provides four analog-to-digital converters (ADCs) with input and
eight digital-to-analog converters (DACs) with single-ended output
using the Analog Devices, Inc., patented multibit sigma-delta (Σ-Δ)
architecture. An SPI port is included, allowing a microcontroller
to adjust volume and many other parameters.
The AD1938 operates from 3.3 V digital and analog supplies.
The AD1938 is available in a 48-lead (single-ended output)
LQFP package. Other members of this family include a differential DAC output and I2C® control port version.
The AD1938 is designed for low EMI. This consideration is
apparent in both the system and circuit design architectures.
By using the on-board PLL to derive the master clock from
the LR clock or from an external crystal, the AD1938 eliminates the need for a separate high frequency master clock and
can also be used with a suppressed bit clock. The DACs and
ADCs are designed using the latest Analog Devices continuous
time architectures to further minimize EMI. By using 3.3 V
supplies, power consumption is minimized, further reducing
emissions.
APPLICATIONS
Automotive audio systems
Home Theater Systems
Set-top boxes
Digital audio effects processors
FUNCTIONAL BLOCK DIAGRAM
DIGITAL AUDIO
INPUT/OUTPUT
AD1938
SERIAL DATA PORT
DAC
DAC
SDATA
OUT
ADC
ANALOG
AUDIO
INPUTS
ADC
CLOCKS
DIGITAL
FILTER
ADC
SDATA
IN
TIMING MANAGEMENT
AND CONTROL
(CLOCK AND PLL)
ADC
DAC
DIGITAL
FILTER
AND
VOLUME
CONTROL
DAC
DAC
ANALOG
AUDIO
OUTPUTS
DAC
DAC
DAC
CONTROL DATA
INPUT/OUTPUT
05582-001
PRECISION
VOLTAGE
REFERENCE
SPI CONTROL PORT
Figure 1.
Rev. E
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Tel: 781.329.4700 ©2006–2013 Analog Devices, Inc. All rights reserved.
Technical Support
www.analog.com
AD1938
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Analog-to-Digital Converters (ADCs) .................................... 13
Applications ....................................................................................... 1
Digital-to-Analog Converters (DACs) .................................... 13
General Description ......................................................................... 1
Clock Signals ............................................................................... 13
Functional Block Diagram .............................................................. 1
Reset and Power-Down ............................................................. 14
Revision History ............................................................................... 2
Serial Control Port ..................................................................... 14
Specifications..................................................................................... 3
Power Supply and Voltage Reference....................................... 15
Test Conditions ............................................................................. 3
Serial Data Ports—Data Format ............................................... 15
Analog Performance Specifications ........................................... 3
Time-Division Multiplexed (TDM) Modes ............................ 15
Crystal Oscillator Specifications................................................. 4
Daisy-Chain Mode ..................................................................... 19
Digital Input/Output Specifications........................................... 5
Control Registers ............................................................................ 24
Power Supply Specifications........................................................ 5
Definitions ................................................................................... 24
Digital Filters ................................................................................. 6
PLL and Clock Control Registers ............................................. 24
Timing Specifications .................................................................. 7
DAC Control Registers .............................................................. 25
Absolute Maximum Ratings ............................................................ 8
ADC Control Registers.............................................................. 27
Thermal Resistance ...................................................................... 8
Additional Modes ....................................................................... 29
ESD Caution .................................................................................. 8
Applications Circuits...................................................................... 30
Pin Configuration and Function Descriptions ............................. 9
Outline Dimensions ....................................................................... 31
Typical Performance Characteristics ........................................... 11
Ordering Guide .......................................................................... 31
Theory of Operation ...................................................................... 13
REVISION HISTORY
7/08—Rev. 0 to Rev. A
2/13—Rev. D to Rev. E
Change to tCLH Parameter, Table 7 .................................................. 7
Changes to Table 7.............................................................................7
Changes to Figure 2 ...........................................................................9
Changes to Table 10 ..........................................................................9
Changes to Clock Signals Section ................................................ 13
Changes to Reset and Power-Down Section ............................... 14
Change to Serial Control Port Section ........................................ 14
Changes to Table 11 ....................................................................... 14
Changes to Figure 24 and Figure 25 ............................................ 22
Changes to Figure 26...................................................................... 23
Changes to Definitions Section .................................................... 24
Changes to Table 16 ....................................................................... 24
Change to Additional Modes Section .......................................... 29
Change to Figure 30 ....................................................................... 30
7/11—Rev. C to Rev. D
Changes to Table 10, DSDATAx/ASDATAx Pin Descriptions ... 9
1/11—Rev. B to Rev. C
Added Automotive Information ................................. Throughout
Change to Table 2, Introductory Text ............................................ 4
Change to Table 4, Introductory Text ............................................ 5
Change to Table 7, Introductory Text ............................................ 7
Changes to Ordering Guide .......................................................... 31
8/09—Rev. A to Rev. B
Changes to Table 16 Title............................................................... 24
Changes to Figure 18 and Table 19 Titles .................................... 25
Changes to Table 20 Title............................................................... 26
Changes to Table 23 and Table 24 Titles ...................................... 27
Changes to Table 25 Title............................................................... 28
Changes to Ordering Guide .......................................................... 31
5/06—Revision 0: Initial Version
Rev. E | Page 2 of 32
Data Sheet
AD1938
SPECIFICATIONS
TEST CONDITIONS
Performance of all channels is identical, exclusive of the interchannel gain mismatch and interchannel phase deviation specifications.
Supply voltages (AVDD, DVDD)
Temperature range1
Master clock
Input sample rate
Measurement bandwidth
Word width
Load capacitance (digital output)
Load current (digital output)
Input voltage high
Input voltage low
1
3.3 V
as specified in Table 1 and Table 2
12.288 MHz (48 kHz fS, 256 × fS mode)
48 kHz
20 Hz to 20 kHz
24 bits
20 pF
±1 mA or 1.5 kΩ to ½ DVDD supply
2.0 V
0.8 V
Functionally guaranteed at −40°C to +125°C case temperature.
ANALOG PERFORMANCE SPECIFICATIONS
Specifications guaranteed at an ambient temperature of 25°C.
Table 1.
Parameter
ANALOG-TO-DIGITAL CONVERTERS
ADC Resolution
Dynamic Range
No Filter (RMS)
With A-Weighted Filter (RMS)
Total Harmonic Distortion + Noise
Full-Scale Input Voltage (Differential)
Gain Error
Interchannel Gain Mismatch
Offset Error
Gain Drift
Interchannel Isolation
CMRR
Input Resistance
Input Capacitance
Input Common-Mode Bias Voltage
DIGITAL-TO-ANALOG CONVERTERS
Dynamic Range
No Filter (RMS)
With A-Weighted Filter (RMS)
With A-Weighted Filter (Average)
Total Harmonic Distortion + Noise
Single-Ended Version
Single-Ended Version
Full-Scale Output Voltage
Gain Error
Interchannel Gain Mismatch
Offset Error
Gain Drift
Conditions
Min
All ADCs
20 Hz to 20 kHz, −60 dB input
98
100
−1 dBFS
−10
−0.25
−10
100 mV rms, 1 kHz
100 mV rms, 20 kHz
Typ
Max
Unit
24
Bits
102
105
−96
1.9
dB
dB
dB
V rms
%
dB
mV
ppm/°C
dB
dB
dB
kΩ
pF
V
0
100
−110
55
55
14
10
1.5
−87
+10
+0.25
+10
20 Hz to 20 kHz, −60 dB input
98
100
0 dBFS
Two channels running
Eight channels running
−92
−86
0.88 (2.48)
−10
−0.2
−25
−30
Rev. E | Page 3 of 32
104
106
108
−4
dB
dB
dB
−75
+10
+0.2
+25
+30
dB
dB
V rms (V p-p)
%
dB
mV
ppm/°C
AD1938
Parameter
Interchannel Isolation
Interchannel Phase Deviation
Volume Control Step
Volume Control Range
De-emphasis Gain Error
Output Resistance at Each Pin
REFERENCE
Internal Reference Voltage
External Reference Voltage
Common-Mode Reference Output
Data Sheet
Conditions
Min
Typ
100
0
0.375
95
Max
±0.6
100
FILTR pin
FILTR pin
CM pin
1.32
1.50
1.50
1.50
Min
Typ
1.68
Unit
dB
Degrees
dB
dB
dB
Ω
V
V
V
Specifications measured at a case temperature of 125°C.
Table 2.
Parameter
ANALOG-TO-DIGITAL CONVERTERS
ADC Resolution
Dynamic Range
No Filter (RMS)
With A-Weighted Filter (RMS)
Total Harmonic Distortion + Noise
Full-Scale Input Voltage (Differential)
Gain Error
Interchannel Gain Mismatch
Offset Error
DIGITAL-TO-ANALOG CONVERTERS
Dynamic Range
No Filter (RMS)
With A-Weighted Filter (RMS)
With A-Weighted Filter (Average)
Total Harmonic Distortion + Noise
Single-Ended Version
Single-Ended Version
Full-Scale Output Voltage
Gain Error
Interchannel Gain Mismatch
Offset Error
Gain Drift
REFERENCE
Internal Reference Voltage
External Reference Voltage
Common-Mode Reference Output
Conditions
All ADCs
20 Hz to 20 kHz, −60 dB input
95
97
−1 dBFS
−10
−0.25
−10
Max
24
Bits
102
105
−96
1.9
dB
dB
dB
V rms
%
dB
mV
0
−87
+10
+0.25
+10
20 Hz to 20 kHz, −60 dB input
98
100
0 dBFS
Two channels running
Eight channels running
104
106
108
−92
−86
0.8775 (2.482)
−10
−0.2
−25
−30
FILTR pin
FILTR pin
CM pin
1.32
−4
1.50
1.50
1.50
dB
dB
dB
−70
+10
+0.2
25
30
1.68
CRYSTAL OSCILLATOR SPECIFICATIONS
Table 3.
Parameter
Transconductance
Unit
Min
Typ
3.5
Rev. E | Page 4 of 32
Max
Unit
mmhos
dB
dB
V rms (V p-p)
%
dB
mV
ppm/°C
V
V
V
Data Sheet
AD1938
DIGITAL INPUT/OUTPUT SPECIFICATIONS
−40°C < TC < +125°C, DVDD = 3.3 V ± 10%.
Table 4.
Parameter
High Level Input Voltage (VIH)
High Level Input Voltage (VIH)
Low Level Input Voltage (VIL)
Input Leakage
High Level Output Voltage (VOH)
Low Level Output Voltage (VOL)
Input Capacitance
Conditions/Comments
MCLKI/XI pin
IIH @ VIH = 2.4 V
IIL @ VIL = 0.8 V
IOH = 1 mA
IOL = 1 mA
Min
2.0
2.2
Typ
Max
0.4
5
Unit
V
V
V
µA
µA
V
V
pF
0.8
10
10
DVDD − 0.60
POWER SUPPLY SPECIFICATIONS
Table 5.
Parameter
SUPPLIES
Voltage
Digital Current
Normal Operation
Power-Down
Analog Current
Normal Operation
Power-Down
DISSIPATION
Operation
All Supplies
Digital Supply
Analog Supply
Power-Down, All Supplies
POWER SUPPLY REJECTION RATIO
Signal at Analog Supply Pins
Conditions/Comments
Min
Typ
Max
Unit
DVDD
AVDD
Master clock = 256 fS
fS = 48 kHz
fS = 96 kHz
fS = 192 kHz
fS = 48 kHz to 192 kHz
3.0
3.0
3.3
3.3
3.6
3.6
V
V
56
65
95
2.0
mA
mA
mA
mA
74
23
mA
mA
429
185
244
83
mW
mW
mW
mW
50
50
dB
dB
Master clock = 256 fS, 48 kHz
1 kHz, 200 mV p-p
20 kHz, 200 mV p-p
Rev. E | Page 5 of 32
AD1938
Data Sheet
DIGITAL FILTERS
Table 6.
Parameter
ADC DECIMATION FILTER
Pass Band
Pass-Band Ripple
Transition Band
Stop Band
Stop-Band Attenuation
Group Delay
DAC INTERPOLATION FILTER
Pass Band
Pass-Band Ripple
Transition Band
Stop Band
Stop-Band Attenuation
Group Delay
Mode
All modes, typical @ 48 kHz
Factor
Min
0.4375 fS
Typ
Max
21
±0.015
24
27
0.5 fS
0.5625 fS
kHz
dB
kHz
kHz
dB
µs
79
22.9844/fS
48 kHz mode, typical @ 48 kHz
96 kHz mode, typical @ 96 kHz
192 kHz mode, typical @ 192 kHz
48 kHz mode, typical @ 48 kHz
96 kHz mode, typical @ 96 kHz
192 kHz mode, typical @ 192 kHz
48 kHz mode, typical @ 48 kHz
96 kHz mode, typical @ 96 kHz
192 kHz mode, typical @ 192 kHz
48 kHz mode, typical @ 48 kHz
96 kHz mode, typical @ 96 kHz
192 kHz mode, typical @ 192 kHz
48 kHz mode, typical @ 48 kHz
96 kHz mode, typical @ 96 kHz
192 kHz mode, typical @ 192 kHz
48 kHz mode, typical @ 48 kHz
96 kHz mode, typical @ 96 kHz
192 kHz mode, typical @ 192 kHz
Rev. E | Page 6 of 32
0.4535 fS
0.3646 fS
0.3646 fS
479
22
35
70
±0.01
±0.05
±0.1
0.5 fS
0.5 fS
0.5 fS
0.5465 fS
0.6354 fS
0.6354 fS
24
48
96
26
61
122
70
70
70
25/fS
11/fS
8/fS
521
115
42
Unit
kHz
kHz
kHz
dB
dB
dB
kHz
kHz
kHz
kHz
kHz
kHz
dB
dB
dB
µs
µs
µs
Data Sheet
AD1938
TIMING SPECIFICATIONS
−40°C < TC < +125°C, DVDD = 3.3 V ± 10%.
Table 7.
Parameter
INPUT MASTER CLOCK (MCLK) AND RESET
tMH
Condition
Comments
Min
Max
Unit
MCLK duty cycle
DAC/ADC clock source = PLL clock @ 256 fS,
384 fS, 512 fS, and 768 fS
DAC/ADC clock source = direct MCLK @ 512 fS
(bypass on-chip PLL)
PLL mode, 256 fS reference
Direct 512 fS mode
40
60
%
40
60
%
6.9
13.8
27.6
MHz
MHz
ns
tMCLK
10
60
ms
%
tMH
fMCLK
fMCLK
tPDR
tPDRR
PLL
Lock time
256 fS VCO Clock, Output Duty Cycle,
MCLKO/XO Pin
SPI PORT
tCCH
tCCL
fCCLK
tCDS
tCDH
tCLS
tCLH
tCLH
tCOE
tCOD
tCOH
tCOTS
DAC SERIAL PORT
tDBH
tDBL
tDLS
tDLH
tDLS
tDDS
tDDH
ADC SERIAL PORT
tABH
tABL
tALS
tALH
tALS
tABDD
AUXILIARY INTERFACE
tAXDS
tAXDH
tDXDD
tXBH
tXBL
tDLS
tDLH
MCLK frequency
RST low
RST recovery
Reset to active output
15
4096
MCLK and LR clock input
40
See Figure 11
CCLK high
CCLK low
CCLK frequency
CIN setup
CIN hold
CLATCH setup
CLATCH hold
CLATCH high
COUT enable
COUT delay
COUT hold
COUT tristate
DBCLK high
DBCLK low
DLRCLK setup
DLRCLK hold
DLRCLK skew
DSDATA setup
DSDATA hold
ABCLK high
ABCLK low
ALRCLK setup
ALRCLK hold
ALRCLK skew
ASDATA delay
AAUXDATA setup
AAUXDATA hold
DAUXDATA delay
AUXBCLK high
AUXBCLK low
AUXLRCLK setup
AUXLRCLK hold
35
35
fCCLK = 1/tCCP, only tCCP shown in Figure 11
To CCLK rising
From CCLK rising
To CCLK rising
From CCLK rising
Not shown in Figure 11
From CCLK falling
From CCLK falling
From CCLK falling, not shown in Figure 11
From CCLK falling
See Figure 24
Slave mode
Slave mode
To DBCLK rising, slave mode
From DBCLK rising, slave mode
From DBCLK falling, master mode
To DBCLK rising
From DBCLK rising
See Figure 25
Slave mode
Slave mode
To ABCLK rising, slave mode
From ABCLK rising, slave mode
From ABCLK falling, master mode
From ABCLK falling
To AUXBCLK rising
From AUXBCLK rising
From AUXBCLK falling
To AUXBCLK rising
From AUXBCLK rising
Rev. E | Page 7 of 32
10
10
10
10
10
10
30
30
30
30
10
10
10
5
−8
10
5
10
10
10
5
−8
+8
+8
18
10
5
18
10
10
10
5
ns
ns
MHz
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
AD1938
Data Sheet
ABSOLUTE MAXIMUM RATINGS
THERMAL RESISTANCE
Table 8.
Parameter
Analog (AVDD)
Digital (DVDD)
Input Current (Except Supply Pins)
Analog Input Voltage (Signal Pins)
Digital Input Voltage (Signal Pins)
Operating Temperature Range (Case)
Storage Temperature Range
Rating
−0.3 V to +3.6 V
−0.3 V to +3.6 V
±20 mA
–0.3 V to AVDD + 0.3 V
−0.3 V to DVDD + 0.3 V
−40°C to +125°C
−65°C to +150°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 indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
θJA represents thermal resistance, junction-to-ambient; θJC
represents the thermal resistance, junction-to-case. All
characteristics are for a 4-layer board.
Table 9. Thermal Resistance
Package Type
48-Lead LQFP
ESD CAUTION
Rev. E | Page 8 of 32
θJA
50.1
θJC
17
Unit
°C/W
Data Sheet
AD1938
ADC2LP
ADC1RN
ADC1RP
ADC1LN
ADC1LP
CM
AVDD
46
45
44
43
42
41
40
39
38
37
AGND
1
36
AGND
MCLKI/XI
2
35
FILTR
MCLKO/XO
3
34
AGND
AGND
4
33
AVDD
AVDD
5
AD1938
32
AGND
OL3
6
31
OR2
OR3
TOP VIEW
(Not to Scale)
7
30
OL2
OL4
8
29
OR1
OR4
9
28
OL1
PD/RST 10
27
CLATCH
DSDATA4 11
26
CCLK
DGND 12
25
DGND
18
19
20
21
22
23
24
ASDATA1
ABCLK
ALRCLK
CIN
COUT
DSDATA1
17
ASDATA2
16
DBCLK
15
DLRCLK
14
DSDATA2
DVDD
13
DSDATA3
SINGLE-ENDED
OUTPUT
05582-002
ADC2LN
47
ADC2RN
LF
48
ADC2RP
AVDD
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
Figure 2. Pin Configuration, 48-Lead LQFP
Table 10. Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
9
10
11
In/Out
I
I
O
I
I
O
O
O
O
I
I/O
Mnemonic
AGND
MCLKI/XI
MCLKO/XO
AGND
AVDD
OL3
OR3
OL4
OR4
PD/RST
DSDATA4
12
13
14
I
I
I/O
DGND
DVDD
DSDATA3
15
I/O
DSDATA2
16
17
18
19
I
I/O
I/O
I/O
DSDATA1
DBCLK
DLRCLK
ASDATA2
20
21
22
23
24
25
O
I/O
I/O
I
I/O
I
ASDATA1
ABCLK
ALRCLK
CIN
COUT
DGND
Description
Analog Ground.
Master Clock Input/Crystal Oscillator Input.
Master Clock Output/Crystal Oscillator Output.
Analog Ground.
Analog Power Supply. Connect to analog 3.3 V supply.
DAC 3 Left Output.
DAC 3 Right Output.
DAC 4 Left Output.
DAC 4 Right Output.
Power-Down Reset (Active Low).
DAC Serial Input 4. Data input to DAC4 data in/TDM DAC2 data out (dual-line mode)/AUX DAC2 data
out (to external DAC2).
Digital Ground.
Digital Power Supply. Connect to digital 3.3 V supply.
DAC Serial Input 3. Data input to DAC3 data in/TDM DAC2 data in (dual-line mode)/AUX ADC2 data
in (from external ADC2).
DAC Serial Input 2. Data input to DAC2 data in/TDM DAC data out/AUX ADC1 data in (from external
ADC1).
DAC Serial Data Input 1. Data input to DAC1 data in/TDM DAC data in/TDM data in.
Bit Clock for DACs.
LR Clock for DACs.
ADC Serial Data Output 2. Data output from ADC2/TDM ADC data in/AUX DAC1 data out (to external
DAC1).
ADC Serial Data Output 1. Data output from ADC1/TDM ADC data out/TDM data out.
Bit Clock for ADCs.
LR Clock for ADCs.
Control Data Input (SPI).
Control Data Output (SPI).
Digital Ground.
Rev. E | Page 9 of 32
AD1938
Pin No.
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
In/Out
I
I
O
O
O
O
I
I
I
O
I
I
O
I
I
I
I
I
I
I
I
O
I
Data Sheet
Mnemonic
CCLK
CLATCH
OL1
OR1
OL2
OR2
AGND
AVDD
AGND
FILTR
AGND
AVDD
CM
ADC1LP
ADC1LN
ADC1RP
ADC1RN
ADC2LP
ADC2LN
ADC2RP
ADC2RN
LF
AVDD
Description
Control Clock Input (SPI).
Latch Input for Control Data (SPI).
DAC 1 Left Output.
DAC 1 Right Output.
DAC 2 Left Output.
DAC 2 Right Output.
Analog Ground.
Analog Power Supply. Connect to analog 3.3 V supply.
Analog Ground.
Voltage Reference Filter Capacitor Connection. Bypass with 10 µF||100 nF to AGND.
Analog Ground.
Analog Power Supply. Connect to analog 3.3 V supply.
Common-Mode Reference Filter Capacitor Connection. Bypass with 47 µF||100 nF to AGND.
ADC1 Left Positive Input.
ADC1 Left Negative Input.
ADC1 Right Positive Input.
ADC1 Right Negative Input.
ADC2 Left Positive Input.
ADC2 Left Negative Input.
ADC2 Right Positive Input.
ADC2 Right Negative Input.
PLL Loop Filter, Return to AVDD.
Analog Power Supply. Connect to analog 3.3 V supply.
Rev. E | Page 10 of 32
Data Sheet
AD1938
TYPICAL PERFORMANCE CHARACTERISTICS
0.10
0
0.08
0.06
MAGNITUDE (dB)
MAGNITUDE (dB)
0.04
0.02
0
–0.02
–0.04
–50
–100
–0.08
–0.10
0
05582-006
05582-003
–0.06
–150
0
2000 4000 6000 8000 10000 12000 14000 16000 18000
12
24
36
48
FREQUENCY (kHz)
FREQUENCY (Hz)
Figure 3. ADC Pass-Band Filter Response, 48 kHz
Figure 6. DAC Stop-Band Filter Response, 48 kHz
0.10
0
–10
–20
0.05
MAGNITUDE (dB)
MAGNITUDE (dB)
–30
–40
–50
–60
–70
0
–0.05
–90
–100
0
05582-007
05582-004
–80
–0.10
5000 10000 15000 20000 25000 30000 35000 40000
0
24
FREQUENCY (Hz)
48
72
96
FREQUENCY (kHz)
Figure 4. ADC Stop-Band Filter Response, 48 kHz
Figure 7. DAC Pass-Band Filter Response, 96 kHz
0.06
0
MAGNITUDE (dB)
0.02
0
–0.02
–50
–100
–0.06
0
8
16
05582-008
–0.04
05582-005
MAGNITUDE (dB)
0.04
–150
0
24
24
48
72
FREQUENCY (kHz)
FREQUENCY (kHz)
Figure 5. DAC Pass-Band Filter Response, 48 kHz
Figure 8. DAC Stop-Band Filter Response, 96 kHz
Rev. E | Page 11 of 32
96
AD1938
Data Sheet
0.5
0
0.4
0.3
–2
MAGNITUDE (dB)
0.1
0
–0.1
–4
–6
–0.2
–0.4
–0.5
0
8
16
32
64
–10
48
05582-010
–8
–0.3
05582-009
MAGNITUDE (dB)
0.2
64
80
FREQUENCY (kHz)
FREQUENCY (kHz)
Figure 10. DAC Stop-Band Filter Response, 192 kHz
Figure 9. DAC Pass-Band Filter Response, 192 kHz
Rev. E | Page 12 of 32
96
Data Sheet
AD1938
THEORY OF OPERATION
ANALOG-TO-DIGITAL CONVERTERS (ADCS)
There are four ADC channels in the AD1938 configured as two
stereo pairs with differential inputs. The ADCs can operate at a
nominal sample rate of 48 kHz, 96 kHz, or 192 kHz. The ADCs
include on-board digital antialiasing filters with 79 dB stopband attenuation and linear phase response, operating at an
oversampling ratio of 128 (48 kHz, 96 kHz, and 192 kHz
modes). Digital outputs are supplied through two serial data
output pins (one for each stereo pair) and a common frame
clock (ALRCLK) and bit clock (ABCLK). Alternatively, one of
the TDM modes can be used to access up to 16 channels on a
single TDM data line.
The ADCs must be driven from a differential signal source for
best performance. The input pins of the ADCs connect to internal switched capacitors. To isolate the external driving op amp
from the glitches caused by the internal switched capacitors,
each input pin should be isolated by using a series connected,
external, 100 Ω resistor together with a 1 nF capacitor connected
from each input to ground. This capacitor must be of high quality,
for example, ceramic NPO or polypropylene film.
The differential inputs have a nominal common-mode voltage
of 1.5 V. The voltage at the common-mode reference pin (CM)
can be used to bias external op amps to buffer the input signals
(see the Power Supply and Voltage Reference section). The
inputs can also be ac-coupled and do not need an external dc
bias to CM.
A digital high-pass filter can be switched in line with the ADCs
under serial control to remove residual dc offsets. It has a
1.4 Hz, 6 dB per octave cutoff at a 48 kHz sample rate. The
cutoff frequency scales directly with sample frequency.
DIGITAL-TO-ANALOG CONVERTERS (DACS)
The AD1938 DAC channels are arranged as single-ended, four
stereo pairs giving eight analog outputs for minimum external
components. The DACs include on-board digital reconstruction
filters with 70 dB stop-band attenuation and linear phase response,
operating at an oversampling ratio of 4 (48 kHz or 96 kHz modes)
or 2 (192 kHz mode). Each channel has its own independently
programmable attenuator, adjustable in 255 steps in increments
of 0.375 dB. Digital inputs are supplied through four serial data
input pins (one for each stereo pair), a common frame clock
(DLRCLK), and a bit clock (DBCLK). Alternatively, one of the
TDM modes can be used to access up to 16 channels on a single
TDM data line.
Each output pin has a nominal common-mode dc level of 1.5 V
and swings ±1.27 V for a 0 dBFS digital input signal. A single op
amp, third-order, external, low-pass filter is recommended to
remove high frequency noise present on the output pins. The
use of op amps with low slew rate or low bandwidth can cause
high frequency noise and tones to fold down into the audio
band; therefore, exercise care in selecting these components.
The voltage at CM, the common-mode reference pin, can be
used to bias the external op amps that buffer the output signals
(see the Power Supply and Voltage Reference section).
CLOCK SIGNALS
The on-chip phase locked loop (PLL) can be selected to
reference the input sample rate from either of the LRCLK pins
or 256, 384, 512, or 768 times the sample rate, referenced to the
48 kHz mode from the MCLKI/XI pin. The default at power-up
is 256 × fS from the MCLKI/XI pin. In 96 kHz mode, the master
clock frequency stays at the same absolute frequency; therefore,
the actual multiplication rate is divided by 2. In 192 kHz mode,
the actual multiplication rate is divided by 4. For example, if a
device in the AD193x family is programmed in 256 × fS mode, the
frequency of the master clock input is 256 × 48 kHz = 12.288 MHz.
If the AD193x is then switched to 96 kHz operation (by writing
to the SPI port), the frequency of the master clock should
remain at 12.288 MHz, which becomes 128 × fS. In 192 kHz
mode, this becomes 64 × fS.
The internal clock for the ADCs is 256 × fS for all clock modes.
The internal clock for the DACs varies by mode: 512 × fS (48 kHz
mode), 256 × fS (96 kHz mode), or 128 × fS (192 kHz mode). By
default, the on-board PLL generates this internal master clock
from an external clock. A direct 512 × fS (referenced to 48 kHz
mode) master clock can be used for either the ADCs or DACs if
selected in the PLL and Clock Control 1 register.
Note that it is not possible to use a direct clock for the ADCs set
to the 192 kHz mode. It is required that the on-chip PLL be
used in this mode.
The PLL can be powered down in the PLL and Clock Control 0
register. To ensure reliable locking when changing PLL modes,
or if the reference clock is unstable at power-on, power down
the PLL and then power it back up when the reference clock
stabilizes.
The internal master clock can be disabled in the PLL and Clock
Control 0 register to reduce power dissipation when the
AD1938 is idle. The clock should be stable before it is enabled.
Unless a standalone mode is selected (see the Serial Control
Port section), the clock is disabled by reset and must be enabled
by writing to the SPI port for normal operation.
To maintain the highest performance possible, limit the clock
jitter of the internal master clock signal to less than a 300 ps rms
time interval error (TIE). Even at these levels, extra noise or
tones can appear in the DAC outputs if the jitter spectrum
contains large spectral peaks. If the internal PLL is not used, it
is best to use an independent crystal oscillator to generate the
master clock. In addition, it is especially important that the
clock signal not pass through an FPGA, CPLD, or other large
digital chip (such as a DSP) before being applied to the
AD1938. In most cases, this induces clock jitter due to the
sharing of common power and ground connections with other
unrelated digital output signals. When the PLL is used, jitter in
Rev. E | Page 13 of 32
AD1938
Data Sheet
the reference clock is attenuated above a certain frequency
depending on the loop filter.
RESET AND POWER-DOWN
The function of the RST pin sets all the control registers to their
default settings. To avoid pops, reset does not power down the
analog outputs. After RST is deasserted, and the PLL acquires
lock condition, an initialization routine runs inside the AD1938.
This initialization lasts for approximately 256 master clock cycles.
The power-down bits in the PLL and Clock Control 0, DAC
Control 1, and ADC Control 1 registers power down the
respective sections. All other register settings are retained. To
guarantee proper start up, the RST pin should be pulled low by
an external resistor.
SERIAL CONTROL PORT
The AD1938 has an SPI control port that permits programming
and reading back of the internal control registers for the ADCs,
DACs, and clock system. There is also a standalone mode
available for operation without serial control that is configured
at reset using the serial control pins. All registers are set to
default, except the internal master clock enable which is set to 1,
and ADC BCLK and LRCLK master/slave is set by the COUT
pin. Refer to Table 11 for details. Standalone mode only
supports stereo mode with an I2S data format and 256 fS master
clock rate. It is recommended to use a weak pull-up resistor on
CLATCH in applications that have a microcontroller. This pullup resistor ensures that the AD1938 recognizes the presence of
a microcontroller.
The SPI control port of the AD1938 is a 4-wire serial control
port. The format is similar to the Motorola SPI format except
the input data-word is 24 bits wide. The serial bit clock and
latch can be completely asynchronous to the sample rate of the
ADCs and DACs. Figure 11 shows the format of the SPI signal.
The first byte is a global address with a read/write bit. For the
AD1938, the address is 0x04, shifted left one bit due to the R/W
bit. The second byte is the AD1938 register address and the
third byte is the data.
Table 11. Standalone Mode Selection
ADC Clocks
Slave
Master
CIN
0
0
COUT
0
1
tCLS
tCCH tCCL
tCCP
CLATCH
CCLK
0
0
CLATCH
0
0
tCLH
tCOTS
CCLK
tCDS tCDH
COUT
D23
D22
D9
tCOE
D9
D8
D0
D8
D0
05582-011
CIN
tCOD
Figure 11. Format of SPI Signal
Rev. E | Page 14 of 32
Data Sheet
AD1938
All digital inputs are compatible with TTL and CMOS levels.
All outputs are driven from the 3.3 V DVDD supply and are
compatible with TTL and 3.3 V CMOS levels.
The ADC and DAC internal voltage reference (VREF) is
brought out on FILTR and should be bypassed as close as
possible to the chip, with a parallel combination of 10 μF and
100 nF. Any external current drawn should be limited to less
than 50 μA.
The internal reference can be disabled in the PLL and Clock
Control 1 register, and FILTR can be driven from an external
source. This configuration can be used to scale the DAC output
to the clipping level of a power amplifier based on its power
supply voltage. The ADC input gain varies by the inverse ratio.
The total gain from ADC input to DAC output remains
constant.
The CM pin is the internal common-mode reference. It should
be bypassed as close as possible to the chip, with a parallel
combination of 47 μF and 100 nF. This voltage can be used to
bias external op amps to the common-mode voltage of the input
and output signal pins. The output current should be limited to
less than 0.5 mA source and 2 mA sink.
TIME-DIVISION MULTIPLEXED (TDM) MODES
The AD1938 serial ports also have several different TDM serial
data modes. The first and most commonly used configurations
are shown in Figure 12 and Figure 13. In Figure 12, the ADC
serial port outputs one data stream consisting of four on-chip
ADCs followed by four unused slots. In Figure 13, the eight
on-chip DAC data slots are packed into one TDM stream. In
this mode, both DBCLK and ABCLK are 256 fS.
The I/O pins of the serial ports are defined according to the
serial mode selected. For a detailed description of the function
of each pin in TDM and auxiliary modes, see Table 12.
The AD1938 allows systems with more than eight DAC channels
to be easily configured by the use of an auxiliary serial data port.
The DAC TDM-AUX mode is shown in Figure 14. In this mode,
the AUX channels are the last four slots of the TDM data stream.
These slots are extracted and output to the AUX serial port. It
should be noted that due to the high DBCLK frequency, this mode
is available only in the 48 kHz/44.1 kHz/32 kHz sample rate.
The AD1938 also allows system configurations with more than
four ADC channels as shown in Figure 15 and Figure 16 that
show using 8 ADCs and 16 ADCs, respectively. Again, due to
the high ABCLK frequency, this mode is available only in the
48 kHz/44.1 kHz/32 kHz sample rate.
Combining the AUX ADC and DAC modes results in a system
configuration of 8 ADCs and 12 DACs. The system, then, consists of two external stereo ADCs, two external stereo DACs,
and one AD1938. This mode is shown in Figure 17 (combined
AUX ADC and DAC modes).
LRCLK
256 BCLKs
BCLK
DATA
SERIAL DATA PORTS—DATA FORMAT
The eight DAC channels use a common serial bit clock (DBCLK)
and a common left-right framing clock (DLRCLK) in the serial
data port. The four ADC channels use a common serial bit
clock (ABCLK) and left-right framing clock (ALRCLK) in the
serial data port. The clock signals are all synchronous with the
sample rate. The normal stereo serial modes are shown in
Figure 23.
The ADC and DAC serial data modes default to I2S. The ports
can also be programmed for left-justified, right-justified, and
TDM modes. The word width is 24 bits by default and can be
programmed for 16 or 20 bits. The DAC serial formats are
programmable according to the DAC Control 0 register. The
polarity of the DBCLK and DLRCLK is programmable according
to DAC Control 1 register. The ADC serial formats and serial
clock polarity are programmable according to ADC Control 1
register. Both DAC and ADC serial ports are programmable to
become the bus masters according to DAC Control 1 register
32 BCLKs
SLOT 1
LEFT 1
SLOT 2
RIGHT 1
SLOT 3
LEFT 2
SLOT 4
RIGHT 2
SLOT 5
SLOT 6
SLOT 7
SLOT 8
SLOT 7
LEFT 4
SLOT 8
RIGHT 4
LRCLK
BCLK
MSB
MSB–1
MSB–2
05582-012
The AD1938 is designed for 3.3 V supplies. Separate power
supply pins are provided for the analog and digital sections.
These pins should be bypassed with 100 nF ceramic chip
capacitors, as close to the pins as possible, to minimize noise
pickup. A bulk aluminum electrolytic capacitor of at least 22 μF
should also be provided on the same PCB as the codec. For
critical applications, improved performance is obtained with
separate supplies for the analog and digital sections. If this is
not possible, it is recommended that the analog and digital
supplies be isolated by means of a ferrite bead in series with
each supply. It is important that the analog supply be as clean
as possible.
and ADC Control 2 register. By default, both ADC and DAC
serial ports are in the slave mode.
DATA
Figure 12. ADC TDM (8-Channel I2S Mode)
LRCLK
256 BCLKs
BCLK
DATA
Rev. E | Page 15 of 32
32 BCLKs
SLOT 1
LEFT 1
SLOT 2
RIGHT 1
SLOT 3
LEFT 2
SLOT 4
RIGHT 2
SLOT 5
LEFT 3
SLOT 6
RIGHT 3
LRCLK
BCLK
MSB
MSB–1
MSB–2
DATA
Figure 13. DAC TDM (8-Channel I2S Mode)
05582-013
POWER SUPPLY AND VOLTAGE REFERENCE
AD1938
Data Sheet
Table 12. Pin Function Changes in TDM-AUX Modes
Mnemonic
ASDATA1
ASDATA2
DSDATA1
DSDATA2
DSDATA3
DSDATA4
ALRCLK
ABCLK
DLRCLK
DBCLK
Stereo Modes
ADC1 Data Out
ADC2 Data Out
DAC1 Data In
DAC2 Data In
DAC3 Data In
DAC4 Data In
ADC LRCLK In/ADC LRCLK Out
ADC BCLK In/ADC BCLK Out
DAC LRCLK In/DAC LRCLK Out
DAC BCLK In/DAC BCLK Out
TDM Modes
ADC TDM Data Out
ADC TDM Data In
DAC TDM Data In
DAC TDM Data Out
DAC TDM Data In 2 (Dual-Line Mode)
DAC TDM Data Out 2 (Dual-Line Mode)
ADC TDM Frame Sync In/DC TDM Frame Sync Out
ADC TDM BCLK In/ADC TDM BCLK Out
DAC TDM Frame Sync In/DAC TDM Frame Sync Out
DAC TDM BCLK In/DAC TDM BCLK Out
AUX Modes
TDM Data Out
AUX Data Out 1 (to Ext. DAC 1)
TDM Data In
AUX Data In 1 (from Ext. ADC 1)
AUX Data In 2 (from Ext. ADC 2)
AUX Data Out 2 (to Ext. DAC 2)
TDM Frame Sync In/TDM Frame Sync Out
TDM BCLK In/TDM BCLK Out
AUX LRCLK In/AUX LRCLK Out
AUX BCLK In/AUX BCLK Out
ALRCLK
ABCLK
DSDATA1
(TDM_IN)
UNUSED SLOTS
EMPTY
EMPTY
EMPTY
AUXILIARY DAC CHANNELS
APPEAR AT
AUX DAC PORTS
8 ON-CHIP DAC CHANNELS
EMPTY
DAC L1
DAC R1
DAC L2
DAC R2
DAC L3
DAC R3
DAC L4
DAC R4
AUX L1
AUX R1
AUX L2
AUX R2
32 BITS
MSB
DLRCLK
(AUX PORT)
LEFT
RIGHT
ASDATA2
(AUX1_OUT)
MSB
MSB
DSDATA4
(AUX2_OUT)
MSB
MSB
Figure 14. 16-Channel AUX DAC Mode
Rev. E | Page 16 of 32
05582-014
DBCLK
(AUX PORT)
Data Sheet
AD1938
ALRCLK
ABCLK
8 ON-CHIP DAC CHANNELS
DSDATA1
(TDM_IN)
DAC L1
ASDATA1
(TDM_OUT)
ADC L1
DAC R1
DAC L2
DAC R2
DAC L3
DAC R3
ADC R2
AUX L1
AUX R1
4 ON-CHIP ADC CHANNELS
ADC R1
ADC L2
DAC L4
DAC R4
4 AUX ADC CHANNELS
AUX L2
AUX R2
32 BITS
MSB
DLRCLK
(AUX PORT)
LEFT
RIGHT
DSDATA2
(AUX1_IN)
MSB
MSB
DSDATA3
(AUX2_IN)
MSB
MSB
05582-015
DBCLK
(AUX PORT)
Figure 15. 8-Channel AUX ADC Mode
ALRCLK
ABCLK
ASDATA1
(TDM_OUT)
4 ON-CHIP ADC CHANNELS
ADC L1
ADC R1
ADC L2
AUXILIARY ADC CHANNELS
ADC R2 AUX L1
AUX R1
AUX L2
UNUSED SLOTS
AUX R2 UNUSED UNUSED UNUSED UNUSED UNUSED UNUSED UNUSED UNUSED
32 BITS
MSB
DLRCLK
(AUX PORT)
LEFT
RIGHT
DSDATA2
(AUX1_IN)
MSB
MSB
DSDATA3
(AUX2_IN)
MSB
MSB
Figure 16. 16-Channel AUX ADC Mode
Rev. E | Page 17 of 32
05582-016
DBCLK
(AUX PORT)
AD1938
Data Sheet
ALRCLK
ABCLK
UNUSED SLOTS
DSDATA1
(TDM_IN)
EMPTY
ASDATA1
(TDM_OUT)
ADC L1
DLRCLK
(AUX PORT)
EMPTY
EMPTY
EMPTY
4 ON-CHIP ADC CHANNELS
ADC R1
ADC L2
AUXILIARY DAC CHANNELS
APPEAR AT
AUX DAC PORTS
8 ON-CHIP DAC CHANNELS
ADC R2
DAC L1
DAC R1
DAC L2
DAC R2
DAC L3
DAC R3
DAC L4
AUXILIARY ADC CHANNELS
AUX L1
AUX R1
AUX L2
DAC R4
AUX L1
AUX R1
AUX L2
AUX R2
UNUSED SLOTS
AUX R2 UNUSED UNUSED UNUSED UNUSED UNUSED UNUSED UNUSED UNUSED
LEFT
RIGHT
DSDATA2
(AUX1_IN)
MSB
MSB
DSDATA3
(AUX2_IN)
MSB
MSB
ASDATA2
(AUX1_OUT)
MSB
MSB
DSDATA4
(AUX2_OUT)
MSB
MSB
Figure 17. Combined AUX DAC and ADC Mode
Rev. E | Page 18 of 32
05582-017
DBCLK
(AUX PORT)
Data Sheet
AD1938
There are two configurations for the ADC port to work in
daisy-chain mode. The first one is with an ABCLK at 256 fS
shown in Figure 21. The second configuration is shown in
Figure 22. Note that in the 512 fS ABCLK mode, the ADC
channels occupy the first eight slots; the second eight slots are
empty. The TDM_IN of the first AD1938 must be grounded in
all modes of operation.
DAISY-CHAIN MODE
The AD1938 allows a daisy-chain configuration to expand the
system to 8 ADCs and 16 DACs (see Figure 18). In this mode,
the DBCLK frequency is 512 fS. The first eight slots of the DAC
TDM data stream belong to the first AD1938 in the chain and
the last eight slots belong to the second AD1938. The second
AD1938 is the device attached to the DSP TDM port.
The I/O pins of the serial ports are defined according to the
serial mode selected. See Table 13 for a detailed description of
the function of each pin. See Figure 26 for a typical AD1938
configuration with two external stereo DACs and two external
stereo ADCs.
To accommodate 16 channels at a 96 kHz sample rate, the
AD1938 can be configured into a dual-line TDM mode as
shown in Figure 19. This mode allows a slower DBCLK than
normally required by the one-line TDM mode.
Again, the first four channels of each TDM input belong to the
first AD1938 in the chain and the last four channels belong to
the second AD1938.
Figure 23 through Figure 25 show the serial mode formats. For
maximum flexibility, the polarity of LRCLK and BCLK are
programmable. In these figures, all of the clocks are shown with
their normal polarity. The default mode is I2S.
The dual-line TDM mode can also be used to send data at a
192 kHz sample rate into the AD1938 as shown in Figure 20.
DLRCLK
DBCLK
8 DAC CHANNELS OF THE FIRST IC IN THE CHAIN
DSDATA1 (TDM_IN)
OF THE SECOND AD193x
DAC L1
DAC R1
DAC L2
DSDATA2 (TDM_OUT)
OF THE SECOND AD193x
THIS IS THE TDM
TO THE FIRST AD193x
DAC R2
DAC L3
DAC R3
DAC L4
DAC R4
8 DAC CHANNELS OF THE SECOND IC IN THE CHAIN
DAC L1
DAC R1
DAC L2
DAC R2
DAC L3
DAC R3
DAC L4
DAC R4
DAC L1
DAC R1
DAC L2
DAC R2
DAC L3
DAC R3
DAC L4
DAC R4
8 UNUSED SLOTS
FIRST
AD193x
SECOND
AD193x
DSP
MSB
Figure 18. Single-Line DAC TDM Daisy-Chain Mode (Applicable to 48 kHz Sample Rate, 16-Channel, Two-AD1938 Daisy Chain)
Rev. E | Page 19 of 32
05582-018
32 BITS
AD1938
Data Sheet
DLRCLK
DBCLK
8 DAC CHANNELS OF THE FIRST IC IN THE CHAIN
DSDATA1
(IN)
DAC L1
DAC R1
DAC L2
8 DAC CHANNELS OF THE SECOND IC IN THE CHAIN
DAC R2
DSDATA2
(OUT)
DSDATA3
(IN)
DAC L3
DAC R3
DAC L4
DAC R4
DSDATA4
(OUT)
DAC L1
DAC R1
DAC L2
DAC R2
DAC L1
DAC R1
DAC L2
DAC R2
DAC L3
DAC R3
DAC L4
DAC R4
DAC L3
DAC R3
DAC L4
DAC R4
32 BITS
FIRST
AD193x
SECOND
AD193x
05582-019
MSB
DSP
Figure 19. Dual-Line DAC TDM Mode (Applicable to 96 kHz Sample Rate, 16-Channel, Two-AD1938 Daisy Chain); DSDATA3 and DSDATA4 Are the Daisy Chain
DLRCLK
DBCLK
DSDATA1
DAC L1
DAC R1
DAC L2
DAC R2
DSDATA2
DAC L3
DAC R3
DAC L4
DAC R4
05582-020
32 BITS
MSB
Figure 20. Dual-Line DAC TDM Mode (Applicable to 192 kHz Sample Rate, 8-Channel Mode)
ALRCLK
ABCLK
4 ADC CHANNELS OF SECOND IC IN THE CHAIN
ASDATA1 (TDM_OUT
OF THE SECOND AD193x
IN THE CHAIN)
ADC L1
ADC R1
ADC L2
ADC R2
ASDATA2 (TDM_IN
OF THE SECOND AD193x
IN THE CHAIN)
ADC L1
ADC R1
ADC L2
ADC R2
4 ADC CHANNELS OF FIRST IC IN THE CHAIN
ADC L1
ADC R1
ADC L2
ADC R2
32 BITS
SECOND
AD193x
DSP
MSB
Figure 21. ADC TDM Daisy-Chain Mode (256 fS BCLK, Two-AD193x Daisy Chain)
Rev. E | Page 20 of 32
05582-021
FIRST
AD193x
Data Sheet
AD1938
ALRCLK
ABCLK
4 ADC CHANNELS OF
SECOND IC IN THE CHAIN
4 ADC CHANNELS OF
FIRST IC IN THE CHAIN
ASDATA1 (TDM_OUT
OF THE SECOND AD193x
IN THE CHAIN)
ADC L1 ADC R1
ADC L2
ADC R2
ASDATA2 (TDM_IN
OF THE SECOND AD193x
IN THE CHAIN)
ADC L1 ADC R1
ADC L2
ADC R2
ADC L1
ADC R1
ADC L2
ADC R2
32 BITS
SECOND
AD193x
DSP
05582-022
FIRST
AD193x
MSB
Figure 22. ADC TDM Daisy-Chain Mode (512 fS BCLK, Two-AD193x Daisy Chain)
LEFT CHANNEL
LRCLK
RIGHT CHANNEL
BCLK
SDATA
LSB
MSB
LSB
MSB
LEFT-JUSTIFIED MODE—16 BITS TO 24 BITS PER CHANNEL
LEFT CHANNEL
LRCLK
RIGHT CHANNEL
BCLK
SDATA
LSB
MSB
LSB
MSB
I2S-JUSTIFIED MODE—16 BITS TO 24 BITS PER CHANNEL
LEFT CHANNEL
LRCLK
RIGHT CHANNEL
BCLK
SDATA
MSB
LSB
MSB
LSB
RIGHT-JUSTIFIED MODE—SELECT NUMBER OF BITS PER CHANNEL
LRCLK
BCLK
MSB
MSB
LSB
LSB
DSP MODE—16 BITS TO 24 BITS PER CHANNEL
1/fS
NOTES
1. DSP MODE DOES NOT IDENTIFY CHANNEL.
2. LRCLK NORMALLY OPERATES AT fS EXCEPT FOR DSP MODE WHICH IS 2 × fS.
3. BCLK FREQUENCY IS NORMALLY 64 × LRCLK BUT MAY BE OPERATED IN BURST MODE.
Figure 23. Stereo Serial Modes
Rev. E | Page 21 of 32
05582-023
SDATA
AD1938
Data Sheet
tDBH
tDBP
DBCLK
tDBL
tDLH
tDLS
DLRCLK
tDDS
DSDATAx
LEFT-JUSTIFIED
MODE
MSB
MSB–1
tDDH
tDDS
DSDATAx
I2S-JUSTIFIED
MODE
MSB
tDDH
tDDS
tDDS
MSB
LSB
tDDH
tDDH
05582-024
DSDATAx
RIGHT-JUSTIFIED
MODE
Figure 24. DAC Serial Timing
tABH
ABCLK
tABL
tALH
tALS
ALRCLK
tABDD
ASDATAx
LEFT-JUSTIFIED
MODE
MSB
MSB–1
tABDD
ASDATAx
I2S-JUSTIFIED
MODE
MSB
ASDATAx
RIGHT-JUSTIFIED
MODE
MSB
Figure 25. ADC Serial Timing
Rev. E | Page 22 of 32
LSB
05582-025
tABDD
Data Sheet
AD1938
Table 13. Pin Function Changes in TDM and AUX Modes (Replication of Table 12)
Stereo Modes
ADC1 Data Out
ADC2 Data Out
DAC1 Data In
DAC2 Data In
DAC3 Data In
DAC4 Data In
ADC LRCLK In/ADC LRCLK Out
ADC BCLK In/ADC BCLK Out
DAC LRCLK In/DAC LRCLK Out
DAC BCLK In/DAC BCLK Out
TDM Modes
ADC TDM Data Out
ADC TDM Data In
DAC TDM Data In
DAC TDM Data Out
DAC TDM Data In 2 (Dual-Line Mode)
DAC TDM Data Out 2 (Dual-Line Mode)
ADC TDM Frame Sync In/DC TDM Frame Sync Out
ADC TDM BCLK In/ADC TDM BCLK Out
DAC TDM Frame Sync In/DAC TDM Frame Sync Out
DAC TDM BCLK In/DAC TDM BCLK Out
TxDATA
TxCLK
TFS (NC)
RxDATA
SHARC®
RxCLK
12.288MHz
LRCLK
AUX
ADC 1
LRCLK
BCLK
DATA
MCLK
AUX Modes
TDM Data Out
AUX Data Out 1 (to Ext. DAC 1)
TDM Data In
AUX Data In 1 (from Ext. ADC 1)
AUX Data In 2 (from Ext. ADC 2)
AUX Data Out 2 (to Ext. DAC 2)
TDM Frame Sync In/TDM Frame Sync Out
TDM BCLK In/TDM BCLK Out
AUX LRCLK In/AUX LRCLK Out
AUX BCLK In/AUX BCLK Out
SHARC IS RUNNING IN SLAVE MODE
(INTERRUPT-DRIVEN)
30MHz
FSYNC-TDM (RFS)
BCLK
ASDATA1 ALRCLK ABCLK DSDATA1
AUX
DATA DAC 1
MCLK
DBCLK
DLRCLK
AD1938
BCLK
DSDATA2
DATA
DSDATA3
TDM MASTER
AUX MASTER
MCLK
MCLKI/XI
LRCLK
AUX
ADC 2
LRCLK
ASDATA2
DSDATA4
BCLK
AUX
DATA DAC 2
MCLK
Figure 26. Example of AUX Mode Connection to SHARC (AD1938 as TDM Master/AUX Master Shown)
Rev. E | Page 23 of 32
05582-026
Mnemonic
ASDATA1
ASDATA2
DSDATA1
DSDATA2
DSDATA3
DSDATA4
ALRCLK
ABCLK
DLRCLK
DBCLK
AD1938
Data Sheet
CONTROL REGISTERS
DEFINITIONS
The global address for the AD1938 is 0x04, shifted left one bit due to the R/W bit. All registers are reset to 0, except for the DAC volume
registers that are set to full volume.
Note that the first setting in each control register parameter is the default setting.
Table 14. Register Format
Bit
Global Address
R/W
Register Address
Data
23:17
16
15:8
7:0
Table 15. Register Addresses and Functions
Address
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Function
PLL and Clock Control 0
PLL and Clock Control 1
DAC Control 0
DAC Control 1
DAC Control 2
DAC individual channel mutes
DAC L1 volume control
DAC R1 volume control
DAC L2 volume control
DAC R2 volume control
DAC L3 volume control
DAC R3 volume control
DAC L4 volume control
DAC R4 volume control
ADC Control 0
ADC Control 1
ADC Control 2
PLL AND CLOCK CONTROL REGISTERS
Table 16. PLL and Clock Control Register 0
Bit
0
2:1
4:3
6:5
7
Value
0
1
00
01
10
11
00
01
10
11
00
01
10
11
0
1
Function
Normal operation
Power-down
INPUT 256 (× 44.1 kHz or 48 kHz)
INPUT 384 (× 44.1 kHz or 48 kHz)
INPUT 512 (× 44.1 kHz or 48 kHz)
INPUT 768 (× 44.1 kHz or 48 kHz)
XTAL oscillator enabled
256 × fS VCO output
512 × fS VCO output
Off
MCLKI/XI
DLRCLK
ALRCLK
Reserved
Disable: ADC and DAC idle
Enable: ADC and DAC active
Description
PLL power-down
MCLKI/XI pin functionality (PLL active), master clock rate setting
MCLKO/XO pin, master clock rate setting
PLL input
Internal master clock enable
Rev. E | Page 24 of 32
Data Sheet
AD1938
Table 17. PLL and Clock Control Register 1
Bit
0
1
2
3
7:4
Value
0
1
0
1
0
1
0
1
0000
Function
PLL clock
MCLK
PLL clock
MCLK
Enabled
Disabled
Not locked
Locked
Reserved
Description
DAC clock source select
ADC clock source select
On-chip voltage reference
PLL lock indicator (read-only)
DAC CONTROL REGISTERS
Table 18. DAC Control Register 0
Bit
0
2:1
5:3
7:6
Value
0
1
00
01
10
11
000
001
010
011
100
101
110
111
00
01
10
11
Function
Normal
Power-down
32 kHz/44.1 kHz/48 kHz
64 kHz/88.2 kHz/96 kHz
128 kHz/176.4 kHz/192 kHz
Reserved
1
0
8
12
16
Reserved
Reserved
Reserved
Stereo (normal)
TDM (daisy chain)
DAC AUX mode (ADC-, DAC-, TDM-coupled)
Dual-line TDM
Description
Power-down
Sample rate
SDATA delay (BCLK periods)
Serial format
Table 19. DAC Control Register 1
Bit
0
2:1
3
4
5
6
7
Value
0
1
00
01
10
11
0
1
0
1
0
1
0
1
0
1
Function
Latch in mid cycle (normal)
Latch in at end of cycle (pipeline)
64 (2 channels)
128 (4 channels)
256 (8 channels)
512 (16 channels)
Left low
Left high
Slave
Master
Slave
Master
DBCLK pin
Internally generated
Normal
Inverted
Description
BCLK active edge (TDM in)
BCLKs per frame
LRCLK polarity
LRCLK master/slave
BCLK master/slave
BCLK source
BCLK polarity
Rev. E | Page 25 of 32
AD1938
Data Sheet
Table 20. DAC Control Register 2
Bit
0
2:1
4:3
5
7:6
Value
0
1
00
01
10
11
00
01
10
11
0
1
00
Function
Unmute
Mute
Flat
48 kHz curve
44.1 kHz curve
32 kHz curve
24
20
Reserved
16
Noninverted
Inverted
Reserved
Description
Master mute
De-emphasis (32 kHz/44.1 kHz/48 kHz mode only)
Word width
DAC output polarity
Table 21. DAC Individual Channel Mutes
Bit
0
1
2
3
4
5
6
7
Value
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Function
Unmute
Mute
Unmute
Mute
Unmute
Mute
Unmute
Mute
Unmute
Mute
Unmute
Mute
Unmute
Mute
Unmute
Mute
Description
DAC 1 left mute
DAC 1 right mute
DAC 2 left mute
DAC 2 right mute
DAC 3 left mute
DAC 3 right mute
DAC 4 left mute
DAC 4 right mute
Table 22. DAC Volume Controls
Bit
7:0
Value
0
1 to 254
255
Function
No attenuation
−3/8 dB per step
Full attenuation
Description
DAC volume control
Rev. E | Page 26 of 32
Data Sheet
AD1938
ADC CONTROL REGISTERS
Table 23. ADC Control Register 0
Bit
0
1
2
3
4
5
7:6
Value
0
1
0
1
0
1
0
1
0
1
0
1
00
01
10
11
Function
Normal
Power down
Off
On
Unmute
Mute
Unmute
Mute
Unmute
Mute
Unmute
Mute
32 kHz/44.1 kHz/48 kHz
64 kHz/88.2 kHz/96 kHz
128 kHz/176.4 kHz/192 kHz
Reserved
Description
Power-down
High-pass filter
ADC L1 mute
ADC R1 mute
ADC L2 mute
ADC R2 mute
Output sample rate
Table 24. ADC Control Register 1
Bit
1:0
4:2
6:5
7
Value
00
01
10
11
000
001
010
011
100
101
110
111
00
01
10
11
0
1
Function
24
20
Reserved
16
1
0
8
12
16
Reserved
Reserved
Reserved
Stereo
TDM (daisy chain)
ADC AUX mode (ADC-, DAC-, TDM-coupled)
Reserved
Latch in mid cycle (normal)
Latch in at end of cycle (pipeline)
Rev. E | Page 27 of 32
Description
Word width
SDATA delay (BCLK periods)
Serial format
BCLK active edge (TDM in)
AD1938
Data Sheet
Table 25. ADC Control Register 2
Bit
0
1
2
3
5:4
6
7
Value
0
1
0
1
0
1
0
1
00
01
10
11
0
1
0
1
Function
50/50 (allows 32, 24, 20, or 16 bit clocks (BCLKs) per channel)
Pulse (32 BCLKs per channel)
Drive out on falling edge (DEF)
Drive out on rising edge
Left low
Left high
Slave
Master
64
128
256
512
Slave
Master
ABCLK pin
Internally generated
Rev. E | Page 28 of 32
Description
LRCLK format
BCLK polarity
LRCLK polarity
LRCLK master/slave
BCLKs per frame
BCLK master/slave
BCLK source
Data Sheet
AD1938
ADDITIONAL MODES
The AD1938 offers several additional modes for board level
design enhancements. To reduce the EMI in board level design,
serial data can be transmitted without an explicit BCLK. See
Figure 27 for an example of a DAC TDM data transmission
mode that does not require high speed DBCLK. This configuration is applicable when the AD1938 master clock is generated
by the PLL with the DLRCLK as the PLL reference frequency.
To relax the requirement for the setup time of the AD1938 in
cases of high speed TDM data transmission, the AD1938 can
latch in the data using the falling edge of DBCLK. This effectively
dedicates the entire BCLK period to the setup time. This mode
is useful in cases where the source has a large delay time in the
serial data driver. Figure 28 shows this pipeline mode of data
transmission.
Both the BLCK-less and pipeline modes are available on the
ADC serial data port.
DLRCLK
32 BITS
INTERNAL
DBCLK
DSDATAx
DLRCLK
05582-027
INTERNAL
DBCLK
TDM-DSDATAx
Figure 27. Serial DAC Data Transmission in TDM Format Without DBCLK
(Applicable Only If PLL Locks to DLRCLK. This Mode Is Also Available in the ADC Serial Data Port.)
DLRCLK
DBCLK
DSDATAx
05582-028
DATA MUST BE VALID
AT THIS BCLK EDGE
MSB
Figure 28. I2S Pipeline Mode in DAC Serial Data Transmission
(Applicable in Stereo and TDM, Useful for High Frequency TDM Transmission.
This Mode Is Also Available in the ADC Serial Data Port.)
Rev. E | Page 29 of 32
AD1938
Data Sheet
APPLICATIONS CIRCUITS
Typical applications circuits are shown in Figure 29 through Figure 32. Figure 29 shows a typical ADC input filter circuit. Recommended
loop filters for LR clock and master clock as the PLL reference are shown in Figure 30. Output filters for the DAC outputs are shown in
Figure 31 and Figure 32 for the noninverting and inverting cases.
120pF
5.76kΩ
5.76kΩ
3
–
1
OP275
+
+
120pF
6
5
OP275
ADCxN
1nF
NPO
DAC OUT
100pF
5.76kΩ
–
240pF
NPO
4.7µF 237Ω
5.76kΩ
1nF
NPO
4.7µF 237Ω
7
ADCxP
+
+
3
4.75kΩ 4.75kΩ
270pF
NPO
11kΩ
+
LF
39nF
DAC
OUT
5.6nF
2.2nF
562Ω
AVDD2
604Ω 4.7µF
–
4.99kΩ
+
3.3nF
NPO
AUDIO
OUTPUT
49.9kΩ
4.99kΩ
68pF
NPO
2
11kΩ
3.01kΩ
VREF
390pF
3.32kΩ
AVDD2
MCLK
270pF
NPO
05582-030
LF
1
Figure 31. Typical DAC Output Filter Circuit (Single-Ended, Noninverting)
Figure 29. Typical ADC Input Filter Circuit
LRCLK
2
+
OP275
05582-031
2
100pF
Figure 30. Recommended Loop Filters for LRCLK and MCLK PLL Reference
0.1µF
3
–
OP275
+
1
604Ω 4.7µF
+
2.2nF
NPO
AUDIO
OUTPUT
49.9kΩ
05582-032
600Z
05582-029
AUDIO
INPUT
Figure 32. Typical DAC Output Filter Circuit (Single-Ended, Inverting)
Rev. E | Page 30 of 32
Data Sheet
AD1938
OUTLINE DIMENSIONS
9.20
9.00 SQ
8.80
1.60
MAX
37
48
36
1
PIN 1
7.20
7.00 SQ
6.80
TOP VIEW
1.45
1.40
1.35
0.15
0.05
0.20
0.09
7°
3.5°
0°
0.08
COPLANARITY
SEATING
PLANE
VIEW A
(PINS DOWN)
25
12
13
VIEW A
0.50
BSC
LEAD PITCH
24
0.27
0.22
0.17
ROTATED 90° CCW
COMPLIANT TO JEDEC STANDARDS MS-026-BBC
051706-A
0.75
0.60
0.45
Figure 33. 48-Lead Low Profile Quad Flat Package [LQFP]
(ST-48)
Dimensions shown in millimeters
ORDERING GUIDE
Model1, 2, 3
AD1938YSTZ
AD1938YSTZRL
AD1938WBSTZ
AD1938WBSTZ-RL
EVAL-AD1938AZ
Temperature Range
–40°C to +105°C
–40°C to +105°C
–40°C to +105°C
–40°C to +105°C
Package Description
48-Lead LQFP
48-Lead LQFP, 13” Tape and Reel
48-Lead LQFP
48-Lead LQFP, 13” Tape and Reel
Evaluation Board
Package Option
ST-48
ST-48
ST-48
ST-48
1
Z = RoHS Compliant Part.
For the AD1938YSTZ, AD1938YSTZRL, AD1938WBSTZ, and AD1938WBSTZ-RL: single-ended output; SPI control port.
3
W = Qualified for Automotive Applications.
2
AUTOMOTIVE PRODUCTS
The AD1938WBSTZ and AD1938WBSTZ-RL models are available with controlled manufacturing to support the quality and reliability
requirements of automotive applications. Note that these automotive models may have specifications that differ from the commercial
models; therefore, designers should review the Specifications section of this data sheet carefully. Only the automotive grade products
shown are available for use in automotive applications. Contact your local Analog Devices account representative for specific product
ordering information and to obtain the specific Automotive Reliability reports for these models.
Rev. E | Page 31 of 32
AD1938
Data Sheet
NOTES
©2006–2013 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05582-0-2/13(E)
Rev. E | Page 32 of 32
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