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WM8740 Schematic ( PDF Datasheet ) - Wolfson Microelectronics plc

Teilenummer WM8740
Beschreibung 24-bit/ High Performance 192kHz Stereo DAC
Hersteller Wolfson Microelectronics plc
Logo Wolfson Microelectronics plc Logo 




Gesamt 27 Seiten
WM8740 Datasheet, Funktion
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WM8740
24-bit, High Performance 192kHz Stereo DAC
DESCRIPTION
The WM8740 is a very high performance stereo DAC
designed for audio applications such as CD, DVD, home
theatre systems, set top boxes and digital TV. The WM8740
supports data input word lengths from 16 to 24-bits and
sampling rates up to 192kHz. The WM8740 consists of a
serial interface port, digital interpolation filter, multi-bit sigma
delta modulator and stereo DAC in a small 28-pin SSOP
package. The WM8740 also includes a digitally controllable
mute and attenuator function on each channel.
The internal digital filter has two selectable roll-off
characteristics. A sharp or slow roll-off can be selected
dependent on application requirements. Additionally, the
internal digital filter can be by-passed and the WM8740
used with an external digital filter.
The WM8740 supports two connection schemes for audio
DAC control. The SPI-compatible serial control port
provides access to a wide range of features including on-
chip mute, attenuation and phase reversal. A hardware
controllable interface is also available.
FEATURES
120dB SNR (‘A’ weighted mono @48kHz), THD+N: -104dB
@ FS
117dB SNR (‘A’ weighted stereo @48kHz), THD+N: -104dB
@ FS
Sampling frequency: 8kHz to 192kHz
Selectable digital filter roll-off
Optional interface to industry standard external filters
Differential mono mode needing no glue logic
Input data word: 16 to 24-bit
Hardware or SPI compatible serial port control modes:
- Hardware mode: mute, de-emphasis, audio format
control
- Serial mode: mute, de-emphasis, attenuation (256
steps), phase reversal
Fully differential voltage outputs
APPLICATIONS
CD, DVD audio
Home theatre systems
Professional audio systems
BLOCK DIAGRAM
WOLFSON MICROELECTRONICS plc
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Production Data, April 2010, Rev 4.4
Copyright ©2010 Wolfson Microelectronics plc






WM8740 Datasheet, Funktion
WM8740
Production Data
RECOMMENDED OPERATING CONDITIONS
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Digital supply range
Analogue supply range
Ground
Difference DGND to AGND
Analogue supply current
Digital supply current
Analogue supply current
Digital supply current
Note:
DVDD
AVDD
AGND, DGND
AVDD = 5V
DVDD = 5V
AVDD = 3.3V
DVDD = 3.3V
-10%
-10%
-0.3
3.3 to 5
3.3 to 5
0
0
13
19
12
12
+10%
+10%
+0.3
V
V
V
V
mA
mA
mA
mA
DVDD must be equal to, or less than the AVDD supply (i.e. DVDD = AVDD = +5V; DVDD = AVDD = +3.3V; DVDD = +3.3V
AVDD = +5V).
ELECTRICAL CHARACTERISTICS
Test Conditions
AVDD, DVDD = 5V, AGND, DGND = 0V, TA = +25oC, fs = 48kHz, SCKI = 256fs unless otherwise stated.
PARAMETER
DAC Circuit Specifications
SNR
(See Note 1)
SYMBOL
THD (full-scale)
(See Note 2)
THD+N (Dynamic range)
(See Note 2)
Filter Characteristics (Sharp Roll-off)
Passband
Stopband
Passband ripple
Stopband attenuation
Delay time
Filter Characteristics (Slow Roll-off)
Passband
Stopband
Passband ripple
Stopband attenuation
Delay time
Internal Analogue Filter
Bandwidth
Passband edge response
Digital Logic Levels
Input LOW level
Input HIGH level
Output LOW level
Output HIGH level
VIL
VIH
VOL
VOH
TEST CONDITIONS
Mono fs @ 48kHz
Stereo fs @ 48kHz
Stereo fs @ 96kHz
Mono 0dB
Stereo 0dB
-60dB
MIN TYP MAX
120
110 117
116
-104
-95 -104
117
±0.0012 dB
-3dB
f > 0.5465fs
±0.001dB
-3dB
f > 0.732fs
-3dB
20kHz
IOL = 2mA
IOH = 2mA
0.4535fs
-82
0.491fs
30/fs
±0.0012
0.274fs
0.459fs
±0.001
-82
9/fs
195
-0.043
2.0
DVDD - 0.3V
0.8
DGND + 0.3V
UNIT
dB
dB
dB
dB
dB
dB
dB
dB
dB
s
dB
dB
s
kHz
dB
V
V
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PD, Rev 4.4, April 2010
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WM8740 pdf, datenblatt
WM8740
Production Data
DEVICE DESCRIPTION
The WM8740 is a high performance 128fs oversampling rate stereo DAC employing a novel 64 level
sigma delta DAC design which provides optimised signal-to-noise performance and clock jitter
tolerance. It is ideally suited to high quality audio applications such as CD, DVD-audio, home theatre
receivers and professional mixing consoles. The WM8740 supports sample rates from 8ks/s to
192ks/s.
The control functions of the WM8740 are either pin selected (hardware mode) or programmed via the
serial interface (software mode). Control functions that are available include: data input word length
and format selection (16-24 bits: I2S, left justified or right justified): de-emphasis sample rate
selection (48kHz, 44.1kHz and 32kHz); differential output modes; a software or hardware mute and
independently digitally controllable attenuation on both channels.
The digital filtering may be bypassed entirely by selecting MODE8X. Data is then input directly to the
DAC, bypassing the digital filters. Left and right channels are input separately, using the MODE pin
as the right channel input. This mode allows the use of alternative digital filters, such as the Pacific
Microsonics PMD100 HDCD filter.
In addition to the normal stereo operating mode the WM8740 may also be used in dual differential
mode with either the left or right channel (selectable) being output dual differentially. Two WM8740s
can then be used in parallel to implement a stereo channel, each supporting a single channel
differentially. Note that this mode uses 2 pairs of differential outputs for each channel – the benefit is
SNR improved by 3dB. This mode is available in both software and hardware modes and may also
be used in conjunction with MODE8X.
SYSTEM CLOCK
Sample rates from 8ks/s up to 96ks/s are available, and automatically selected, with a system clock
of 256fs or 384fs. In addition a system clock of 128fs or 192fs may be used, with sample rates up to
192ks/s. With a 128fs or 192fs system clock 64x oversampling mode operation is automatically
selected and the first stage of the digital filter is bypassed.
WM8740 has an asynchronous monitor circuit, which in the event of removal of the master system
clock, resets the digital filters and analogue circuits, muting the output. Re-application of the system
clock re-starts the filters from an intitialised state. Control registers are not reset under this condition.
The WM8740 is tolerant of asynchronous bit clock jitter. The internal signal processing
resynchronises to the external LRCIN once the phase difference between bit clock and the system
clock exceeds half an LRCIN period. During this re-synch period the interpolating filters will either
miss or repeat an audio sample, minimising the audible effects of the operation. Table 1 shows the
typical system clock frequency inputs for the WM8740.
SAMPLING
RATE
(LRCIN)
128fs
SYSTEM CLOCK FREQUENCY (MHZ)
192fs
256fs
384fs
512fs
32kHz
4.096
6.144
8.192
12.288
16.384
44.1kHz
5.6448
8.467
11.2896
16.9340
22.5792
48kHz
6.114
9.216
12.288
18.432
24.576
96kHz
12.288
18.432
24.576
36.864 Unavailable
192kHz
24.576
36.864 Unavailable Unavailable Unavailable
Table 1 System Clock Frequencies Versus Sampling Rate
768fs
24.576
33.8688
36.864
Unavailable
Unavailable
AUDIO DATA INTERFACE
Data may be input at a rate corresponding to the system clock having a rate of 256fs or 384fs, in
which case an oversampling ratio of 128x is selected. Alternatively a rate of 128fs or 192fs may be
used, in which case the first filter stage is bypassed and an oversampling ratio of 64x results. Finally,
in MODE8X, data may be input at 8x the normal rate, in which case separate input pins are used to
input the two stereo channels of data (unless DIFFHW mode and MODE8X are both selected, in
which case only a mono channel is converted differentially). In MODE8X all filter stages are by-
passed, prior to the sigma delta modulator, MODE8X is not supported at 192kHz sampling rate. Data
is input MSB first in all modes.
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