Cirrus Logic CRD5381 User Manual
CRD5381
Audio A/D Converter w/ Asynchronous Decimation Filter
Reference Design
Features
Analog Performance
Advanced Multi-bit Delta-sigma Architecture
24-bit Conversion
120 dB Dynamic Range
-110 dB THD+N
Performance insensitivity to Input Clock Jitter
Digital Filter Characteristics
125 dB Stop-band Rejection
Phase-Matched Outputs
CS5381 A
LEFT
RIGHT
Quad Speed
Slave Mode
SDOUT
System Features
Output Sample Rate Determined by Input
Word, Left/Right, or Fsync Clock
No External Master Clock Required
Easily Scalable for Additional Channels
Sample Rates from 27 kHz to 192 kHz
Four-Channel Time-Division Multiplexed
Output
Two Independent Stereo, Left-Justified
Outputs
SDIN
CS8421 A
Master Input
Slave Ouput
SDOUT
Differential Analog
Inputs 1-4
http://www.cirrus.com
2
2
TDM ENABLE
SDOUT A
PCM Data Ouput/
Serial Clock Input
22
TDM IN
LEFT
RIGHT
CS5381 B
Quad Speed
Slave Mode
SDOUT
Copyright © Cirrus Logic, Inc. 2005
(All Rights Reserved)
CS8421 B
Master Input
Slave Output
SDOUTSDIN
TDM/SDOUT B
Header, J4
LRCK INPUT SCLK INPUT
MAY ‘05
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CRD5381
Description
The combination of the CS5381 Analog-to-Digital Converter and CS8421 Asynchronous Sample Rate Converter
creates an analog-to-digital conversion system with an asynchronous digital decimation filter that is virtually
immune to interface or network jitter. In addition, the CS8421 adds a multi-channel Time Division Multiplexed
(TDM) output format option. These unique features address many of the issues and design challenge s associated
with networked audio systems and other high-performance applications. In addition to the standard 24-bit audio
data, the CS8421 adds the functionality to output properly dithered 32, 20, or 16-bit data.
The CRD5381 was designed as a platform for easy evaluation of the jitter rejection, sample rate conversion, and
time-division multiplexing capabilities of the CS8421 in the context of a A/D conversion system with an asynchronous decimation filter. The CRD5381 accepts four channels of balanced, analog audio input and provides four
channels of PCM data output. The data output can be either a four-channe l TDM format o r two indep end en t stereo
left-justified data outputs. The PCM data output is synchronous to the serial left-right clock and bit clock that the user
supplies. The CRD5381 also provides status indicators including ADC overflow and SRC unlock, and it accepts an
external reset signal. The only system power requirements for the design include +/- 12 Volts and +3.3 Volts. The
required input signals are a left/right or word clock and serial clock for the audio data output.
This document includes operational instructions and schematics for the CRD5381 and is a comp anion document to
the Cirrus Logic applications note AN270, “Audio A/D conversion with Asynchronous Decimation Filter” [1]. Please
also refer to the CS5381 and CS8421 data sheets for specific product information and specifications [2,3]. Both d ocuments, as well as AN270, are available online at http://www.cirrus.com
The CRD5381 schematic set is shown in Figures 9 through 14 and the board layout is shown in Figures 15
through 19. A block diagram of the CRD5381 is shown in Figure 8.
ORDERING INFORMATION
Product Description Order#
CRD5381 Audio A/D Converter w/ Asynchronous Decimation Filter Reference Design CRD5381
2 DS563RD1
TABLE OF CONTENTS
1. SYSTEM OVERVIEW ................................................................................................................ 4
1.1 Sample Clock Domain ..................................... ... ....................................... ... .... ... ... ... ........ 4
1.1.1 CS8421 Input Operational Mode .......................................................................... 4
1.1.2 CS5381 Operational Mode . ... ... .... ... ... ... .... .......................................... ... ... ... ... ..... 4
1.1.3 Master Clock Frequency Generation .................................................................... 4
1.1.4 Maximum Sample Rate ................. ... ... ... ....................................... ... .... ... ... ... ... .... . 4
1.1.5 Synchronization of Multiple Sections .................................................................... 4
1.2 CS8421 Output and the Interface Clock Domain .............................................................. 5
1.2.1 CS8421 Output System Clocking .................................................... .... ... ... ... ... .... . 5
1.2.2 Serial Audio Output Port Options and Selection of Data Resolution and Dither ... 5
1.2.3 Clocking ........................................................... ... .... ... ...................................... .... . 5
1.2.4 SRC Locking and Varispeed ................................... ... ... ... ... .... ... ... ... .... ... ... ... ... .... . 5
1.2.5 Latency or Group Delay ............................................................. ... ... ..................... 6
1.2.6 Phase Matching Between Multiple Sections ......................................................... 6
1.3 Filter Response ................................................................................................................. 7
2. OPERATION .............................................................................................................................. 9
2.1 Sample Rate ............. .... ... ... ... ....................................... ... .... ... ... ........................................ 9
2.2 Audio Data Output Format Selection ......................... ........................................................ 9
2.3 System Clocking and Data I/O .......................................................................................... 9
2.4 System Status Indicators ................................................................................................. 10
2.5 System Reset ........ ... .... ...................................... .... ... ... ... .... ... ......................................... 10
2.6 Analog Inputs ......... ... .... ... ....................................... ... ... ... .... ... ......................................... 11
2.7 Power ........................................... ... ....................................... ... ... ... .... ... ......................... 11
2.8 Grounding and Power Supply Decoupling ....................................................................... 11
3. BLOCK DIAGRAM .................................................................................................................. 12
4. SCHEMATICS ......................................................................................................................... 13
5. LAYOUT .................................................................................................................................. 19
6. REFERENCES ......................................................................................................................... 24
7. REVISION HISTORY ............................................................................................................... 24
CRD5381
LIST OF FIGURES
Figure 1. Transitional Band, 48 kHz Out.........................................................................................7
Figure 2. Transitional Band, 96 kHz Out.........................................................................................8
Figure 3. Transitional Band, 192 kHz Out....................................................................................... 8
Figure 4. Left-Justified Serial Audio Interface.................................................................................9
Figure 5. TDM Audio Interface........................................................................................................ 9
Figure 6. Clock and Data Header Connections, J4....................................................................... 10
Figure 7. Status Indicator and Reset Header, J16........................................................................ 11
Figure 8. Block Diagram................................................................................................................ 12
Figure 9. Analog Inputs 1 & 2........................................................................................................ 13
Figure 10. Analog Inputs 3 & 4...................................................................................................... 14
Figure 11. CS5381 & CS8421 Pair A............................................................................................ 15
Figure 12. CS5381 & CS8421 Pair B............................................................................................ 16
Figure 13. I/O Header and Miscellaneous..................................................................................... 17
Figure 14. Power........................................................................................................................... 18
Figure 15. Silk Screen................................................................................................................... 19
Figure 16. Top Layer..................................................................................................................... 20
Figure 17. Bottom Layer................................................................................................................ 21
Figure 18. Power Plane................................................................................................................. 22
Figure 19. Ground Plane............................................................................................................... 23
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1. SYSTEM OVERVIEW
1.1 Sample Clock Domain
1.1.1 CS8421 Input Operational Mode
Serial Audio Interface - Left-Justified. The selection of the serial audio interface format is arbitrary, assuming
the serial input format of the CS8421 is in agreement with the serial output format of the CS5381. The selection of the serial audio format is done by connecting a resistor (1.96 k Ω in this application) to either ground
or the VL supply.
System Clocking - Master mode, LRCK = MCLK/128. In this mode, the CS8421 generates the Serial and
Left/Right clocks within the sampling clock domain. This mode is selected by the resistor connected to the
MS_SEL pin of the CS8421. In this application the MS_SEL pin is connected to ground (equivalent to connecting a 1 kΩ resistor to ground).
1.1.2 CS5381 Operational Mode
Serial Audio Interface - Left-Justified. The selection of the serial audio interface format is arbitrary, assuming
the input format of the CS8421 is in agreement with the output format of the CS5381.
System Clocking - Slave mode. In this application the CS8421 generates the serial and Left/Right clocks
within the sampling clock domain.
CRD5381
Operational Mode or Sample Rate Range - Configured for Quad-Speed Mode to support sample rates
above 100 kHz.
High Pass Filter - Enabled
Master Clock Divide - Enabled to divide the master clock by 2.
1.1.3 Master Clock Frequency Generation
The CS8421 uses the clock supplied through its XTI pin as its master clock (MCLK). The CS5381 also uses
this signal as its master clock (through the MCLK pin). Alternatively, the CS8421 can generate a master
clock (via the MCLK_OUT pin) by connecting a crystal across its XTI-XTO pins, which can supply a MCLK
to the CS5381.
In this application, MCLK_OUT pin is not being used and is pulled high through a 47 kΩ resistor to VL to
disable it. If a crystal is not being used, as with the crystal oscillator in this application, XTO should be left
unconnected or pulled low through a 47 kΩ resistor to ground
1.1.4 Maximum Sample Rate
The maximum sample rate is limited by the maximum allowable master clock frequency of the CS8421,
which is 27 MHz. The sample rate is this clock frequency divided by 128. This corresponds to a maximum
sample rate of 210.937 kHz within the sample clock domain. In this application, we have chosen a master
clock frequency of 25 MHz, which corresponds to a sample rate of approximately 195.312 kHz
.
1.1.5 Synchronization of Multiple Sections
In this application multiple CS8421 inputs are set to master mode, and it is important that their serial ports
be aligned in time, with minimum possible phase error. To achieve this, their reset sign als are tied to gether
and routed for minimum skew. The amount of deviation between ILRCKs generated by the respective parts
is typically either 0 or 1 master clock period, or between 0 and 40 ns.
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CRD5381
1.2 CS8421 Output and the Interface Clock Domain
1.2.1 CS8421 Output System Clocking
The CS8421 serial output is configured as a system clock slave. The advantages are:
• Output sample rate is dependent on the frequency o f the incoming word clock ( OLRCK), set by the user.
• Outputs of multiple CS8421 devices are synchronous.
• Multiple devices can be configured in a Time Division Multiplexed (TDM) multi-ch annel interface format.
As mentioned in “CS8421 Input Operational Mode” on page 4, the input of the CS8421 is configured as a
master, with the master clock frequency = 128*Fsi (or ILRCK). To accommodate this serial input mode, and
to set the serial output to slave, the MS_SEL pin is connected to +3.3 V.
1.2.2 Serial Audio Output Port Options and Selection of Data Resolution and Dither
The CS8421 provides multiple options for the serial audio output port. These options include:
• Output Data Format of Left-Justified, Right-Justified, I²S or TDM
• Audio output data resolution of the SRC can be set to 16, 20, 24, or 32-bits. Dithering is applied and is
automatically scaled to the selected output word length. This dither is not correlated between left and
right channels.
Output word-length and serial data format are selected with either a pull- up or pull down re sistor connected
to the SAOF pin of the CS8421. Please refer to Table 3 in the CS8421 data sheet for details [3].
The serial audio output of the CRD5381 is configured to operate in either dual 24-bit Left-Justified formats
or a 4-channel 24-bit TDM output.
1.2.3 Clocking
In order to ensure proper op eration of the CS8 421, the clo ck or crys tal attach ed to XTI m ust simult aneously
satisfy the requirements of LRCK for both the input and output as follows:
• If the input is set to master, Fsi ≤ XTI/128 and Fso ≤ XTI/130.
• If the output is set to master, Fso ≤ XTI/128 and Fsi ≤ XTI/130.
• If both input and output are set to slave, XTI ≥ 130*[maximum(Fsi,Fso)], XTI/Fsi < 3750, and XTI/Fso <
3750.
In the example application in this data sheet, the input serial port is set to master, and generates serial
clocks for a sampling rate of XTI/128. The output serial port is set as slave, and can receive a left-right clock
that is ≤ XTI/130. The serial bit-clock frequency is always 64*left-right clock.
1.2.4 SRC Locking and Varispeed
The SRC calculates the ratio between the input sample rate and the output sample rate, and uses this information to set up various parameters inside the SRC block. The SRC takes approximately 4200/Fso
(8.75 ms at Fso of 48 kHz) to make this calculation.
The SRC_UNLOCK pin is used to indicate when the SRC is not locked. When RST
is a change in Fsi or Fso, SRC_UNLOCK will be set high. The SRC_UNLOCK pin will continue to be high
until the SRC has reacquired lock and settled, at which point it will transition low. When the SRC_UNLOCK
pin is set low, SDOUT is outputting valid audio data. This can be used to signal a DAC to u n-mute its output.
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is asserted, or if there
1.2.5 Latency or Group Delay
The system latency, or group delay, is the sum of the CS5381 group delay and the CS8421 group delay.
The latency of the CS5381 is 5 samples (5/Fs), and the latency o f the CS8421 depends on input and output
sample rates, and can be found in the CS8421 data sheet [3]. Table 1 shows the combined group delay for
typical output sample rates with a fixed input sampling rate of 195.3125 kHz.
.
Output Sample Rate Group Delay
48 kHz 1.48 ms
96 kHz .895 ms
192 kHz .605 ms
Table 1. System Latency
1.2.6 Phase Matching Between Multiple Sections
This phase delay is equal across multiple parts. Therefore, when multiple parts oper ate at the same Fsi and
Fso and use a common XTI/XTO clock, their output data is phase matched.
CRD5381
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CRD5381
1.3 Filter Response
The transition-band response of the CRD5381 is due to the combination of the digital filtering performed by both th e
CS5381 and the CS8421. Due to the superior stop-band rejection of the CS8421, the combination of the two parts
yields a better stop-band rejection then the CS5381 alone. When the output sample rate is close to that of the
CS5381, signals that fall within the transition-band spectrum will already have been aliased down into the pass-band
prior to the CS8421’s output filter. This can be seen in Figure 3 on page 8, where the signals above the notch at
approximately 97.5 kHz represent signals that have been aliased downward prior to th e action of the CS8421 output
filter.
+0
-5
-10
-15
-20
-25
-30
-35
-40
-45
-50
-55
d
B
-60
F
S
-65
-70
-75
-80
-85
-90
-95
-100
-105
-110
-115
-120
20k 26k20.5k 21k 21.5k 22k 22.5k 23k 23.5k 24k 24.5k 25k 25.5k
Hz
Figure 1. Transitional Band, 48 kHz Out
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+0
-5
-10
-15
-20
-25
-30
-35
-40
-45
-50
-55
d
B
-60
F
S
-65
-70
-75
-80
-85
-90
-95
-100
-105
-110
-115
-120
40k 52k41k 42k 43k 44k 45k 46k 47k 48k 49k 50k 51k
Hz
CRD5381
Figure 2. Transitional Band, 96 kHz Out
+0
-5
-10
-15
-20
-25
-30
-35
d
B
-40
F
S
-45
-50
-55
-60
-65
-70
-75
-80
40k 150k50k 60k 70k 80k 90k 100k 110k 120k 130k 140k
Hz
Figure 3. Transitional Band, 192 kHz Out
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