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Power management
for MP3 players
Guy F.K. Cheung
Lawrence H.S. Ling
Integrated Circuits Design Manager
ON Semiconductor
Staff Integrated Circuit Design Engineer
ON Semiconductor
Tze-Kau Man
Indy C.O. Ho
Product Application Engineering Manager
ON Semiconductor
Application Engineer
ON Semiconductor
Abstract
Since the potential market is large, many other competing
products have been emerged in the market by Samsung,
Creative Lab, RCA, Sanyo, and many other start-ups; and the
market start to prosper in spite of the fact that the issue of copy
protection is still pending to solved and there are still some
other file formats for music available in the internet with better
copy protection feature developed by other large companies.
MP3 (MPEG-1/2 Layer3) is a new standard audio file format,
based on how human actually perceive sound, for compressing
a sound sequence into about one-tenth the size of the original
file with unnoticeable loss in sound quality. It can be used in
various fields, like language self-learning aids and Internet
broadcasts, etc.
As the first MP3 player was born in 1998, MP3 officially
landed on the consumer music recording market, and with its
handy outlook and economy overall cost, it gave head-on
punches to traditional CD and MD. And, because it involves no
motor or other form of actuator, it can be small in physical size
and power consumption. This also allow it being integrated into
other consumer systems, a recent successful case is into mobile
phone.
As the electronic system is so light-weighted, power consumption in idle mode or operation mode are very small, in this
case, careful power management design can squeeze the last
drop from the battery to make its weight and size worthwhile.
This is the prime goal of this paper, which the authors will
present the power management approach best suited for this
emerging consumer platform.
MP3 Player and MP3 Format
MP3 Player Background
In general, MP3 player is a kind of internet digital audio player
in the form of electronic device or software program that support the playback of music files in MP3 format, the most well
known and popular audio compression algorithms used in the
internet.
What most people are interested in and this paper is going
to talk about is portable MP3 players. The MP3 player was first
introduced in 1998 by Diamond Multimedia in the form of their
Rio PMP-300. Due to its handy size, light-weighted, skip-proof
audio playback during mechanical vibration (without motor or
any playback mechanism), low power consumption, near
CD-quality music playback (subject to the encoding sampling
frequency and bit rate), and the most important — the music
files can be downloaded from internet web sites or through
e-mail.
MP3 Format
MP3 (MPEG-1/2 Layer3) is an audio compression scheme that
is defined as part of the International Organization for Standardization (ISO) [1] Moving Picture Experts Group (MPEG)
audio/video coding standard. MPEG-1 defined three encoding
schemes, referred to as layer 1, layer 2, and layer 3. Each of
these schemes, with increasing sophisticated encoding techniques, gives better audio quality at a given bit rate correspondingly.
These three layers are hierarchical, that is, a layer 3 decoder
can decode layer 1, 2, and 3 bit streams; a layer 2 decoder can
decode layer 1, and 2 bits streams; a layer 1 decoder can only
decode layer 1 bit streams. Each layer supports decoding compressed audio signals sampled at 48kHz, 44.1kHz, and 32kHz.
MPEG-2 exploits the same kind of codecs but with extended
support for sampling rates at 24kHz, 22.05kHz, and 16kHz and
for more audio channels for surround sound and multilingual
application.
The quality of music encoded in MP3 is mainly determined
by two factors: one is the sampling frequency which has been
discussed, another more important factor is the bit rate which is
the average number of bits used to represent audio signal in
each second. The higher the bit rate, the better is the quality of
the audio signal, but also the larger is the file size for the same
music length. There are two types of bit rate used for the MP3
encoding: constant bit rate encoding and variable bit rate encoding. Constant bit rate encoding is an encoding method which
ensures a consistent bit rate throughout an encoded file, potentially at the expense of audio quality or encoder efficiency.
Whereas, variable bit rate is an encoding method which ensures consistently high audio quality throughout the encoded
file by making intelligent bit allocation decision during the encoding process. The most commonly used constant bit rates are
International IC – China • Conference Proceedings 405
64kbps (FM quality), 96kbps (near CD quality), 128kbps
(CD quality), and 160kbps with over sampling (CD quality).
The compression algorithm exploits the fact of human ear’s
perception to sound, that is, quite sounds are masked out by
loud sounds in the same frequency range. The encoder uses
this fact and removes the information associated with the sound
that cannot be heard anyway from the audio signal. It enables
compression of audio data stored in a standard compact disc to
about 1/10 of it original size.
Market overview
Since the emerging of the MP3 player in 1998, market analysts
all predict a huge growth in portable MP3 player market which
is driven by the wide acceptance of internet as a medium of
music delivery and online commerce. Currently, portable MP3
player market is mainly concentrated in North America which
contributes to over 90% of worldwide shipments last year. However, the regional sales of MP3 players will increase with increasing worldwide Internet access, especially in Asian countries. With the blooming popularity of digital music downloads,
it is estimated that the annual domestic sale of MP3 player in
the US will be increased from a total of $126 million to $1.25
billion by the end of 2002. See figure 1. [2]
Table 1. A Table shows the different formats now being developed
MP3 system overview
A basic MP3 player system consists of a system controller, MP3
decoder, logic interface, on-board Flash memory, Flash card
interface, stereo audio DAC, download port, LCD display, user
interface, and additional value-added features.
Figure 2. A MP3 player system block diagram
Figure 1. Five year revenue forecast of portable MP3 player in the US
In spite of the forecast for tremendous growth in the MP3
market, there are three key dynamics that will affect the market
growth and impact the definition of products:
1. Music file format - Although MP3 is the dominant format for music available in the internet, other formats are
emerging. Several of these new formats were designed
to provide copyright production features that are being
demanded by the music recording industry.
2. Copyright protection - Despite the SDMI (Secure Digital Music Initiative) [3] aims at establishing a technology specification for secure distribution of copyright
materials. There is considerable technical uncertainty
about the implementation timetable. Moreover, the fear
of piracy has limited the availability of legitimate MP3
material and the music tracks from the mainstream artists to rollout.
3. Feature set of MP3 players - The Flash memory is the
cost dominant component in MP3 players and is more or
less the same for all venders. As a result, the price differentiation is constrained. For increasing the perceived
value of a MP3 player, manufacturers have to add valueadded features tailored to the market in their products.
System controller
The system controller performs the system management function. An 8-bit microcontroller is used in simple basic designs
and a separate MP3 decoder and system logic interface are required. While some more integrated new designs used CPLD
(Complex Programmable Logic Device) which includes main
control logic, Flash control, parallel interface, serial interface,
user interface control. Therefore, the system design can be much
simplified. Moreover, some designs use RISC (Reduced Instruction Set Computer) processor which includes fully programmable DSP function supporting a wide range of audio formats,
and a selection of peripheral like Flash interface, LCD interface, serial interface, and parallel interface. Therefore, a separate MP3 decoder and peripheral logic are not required, however, more time may be required for programming the DSP
function.
System Logic Interface
The device is used as system level logic glue interfacing the
microcontroller to memory, the download port, and MP3
decoder.
MP3 decoder
The MP3 decoder decompresses the MP3 bit streams stored in
the Flash memory into audio data and sends the data to stereo
DAC. Some other DSP functions like treble, bass, and volume
control will also be included.
Flash memory
The Flash memory is non-volatile memory that can be read,
reprogrammed, and erased. These operations can be performed
using a single low voltage of 2.7V to 3.6V. The Flash memory
is used for the storage of boot code and application code of the
406 International IC – China • Conference Proceedings
MP3 player, and MP3 music data files. The memory is divided
into blocks which can be erased independently, therefore, it is
possible to preserve valid data while erasing unwanted data.
For data storage, the internal memory is actually contains two
separate Flash memory banks: the song Flash and the starting
address Flash. The song Flash is provided for MP3 songs storage, whereas, the start address Flash stores the starting address
and the end address of each song. MP3 players typical come
with 16MB / 32MB internal Flash memory while some more
advanced MP3 players come with 64MB internal Flash memory.
Flash card interface
It is used for memory expansion for extra song storage with
external memory device in the form of SmartMedia card or
memory stick.
Stereo Audio DAC
High precision dual digital-to-analog converter utilizes conversion technique based on oversampling with noise shaping to
convert uncompressed data from the MP3 decoder into stereo
audio signals. The device usually features with digital volume
control and mute function. Some IC vendors may also
integrate 16Ω/32Ω headphone amplifiers in the DAC.
Download port interface
Both parallel interface and USB (Universal Serial Bus) [4] interface are used in MP3 players in the market. However, the
maximum data transfer through USB is 12Mbps which is about
5 times faster than that through parallel interface. Therefore,
USB interface is growing popular in the market and will become a standard for connecting MP3 player to a PC.
LCD display
The LCD displays used in MP3 players are typically in the size
of 128 x 32 dot matrix type about 1 sq. inch for indication of
song name, track number, play mode, sound effect, playback
elapse time, bit rate, etc.
Value-added Functional Blocks
Voice Recording Function
Most of the MP3 players available in the market are included
with voice recording function. The voice is recorded by a monaural electret condenser microphone and is encoded in ADPCM
(Adaptive Delta Pulse Code Modulation) at 8kHz or 16kHz
sampling rates. The voice recording time is usually about 2hrs.
Voice-recording files are stored in wav format which can be
uploaded back into PC.
EL (Electroluminescent Lamp) Backlite
EL backlighting is now a common LCD lighting in dim environments for portable electronic devices since it is the most
practical and economical way to evenly illuminate LCD displays. Some new MP3 players are now also designed with EL
backlite function.
FM Radio Tuner
FM radio tuners with digital tuning circuit are also available in
some MP3 player models as a value-added feature.
Power requirements of various components
in MP3 player
System Controller
The operating voltage for the system controller can be ranging
from 2.0V to 6.0V and the typical operating voltage is 3.0V or
3.3V. While the operating current is depended on the type of
system controller and the clock speed of the controller used.
For 8-bit or 16-bit micro-controllers and CPLDs at a clock speed
between 1 MHz and 15 MHz, the typical operating current is
around 2 mA to 20 mA. Whereas, 32-bit RISC processors with
MP3 decoder or programmable DSP function, the typical operating current will be between 35 mA and 50 mA at clock speed
of 25 MHz. However, some processors ,like EP7209 from Cirrus
Logic, use split-power for which 2.5V is for the processor
core supply voltage, while 3.3V is for the I/O supply voltage.
Therefore, the power management solution will become a bit
more complicated when using this kind of processor. [5], [6],
[7], [8], [9]
MP3 decoder
The power requirement of the MP3 decoder is usually 2.4V to
3.6V for the supply voltage with 3.3V as the typical value, and
typically requires 30mA operating current. [10], [11]
Stereo DAC
The supply voltage for Stereo DAC used in portable MP3 player
is between 1.8V and 3.6V while the operating current consumption is around 15 mA to 20 mA. [12], [13], [14]
Flash Memory
The Flash memory can be operated at 2.7V to 5.0V and the
typical operating voltage is 3.3V. While the typical operating
current is 10 mA for read, 20 mA for write/erase. Power supply
requirement for such sensitive device demanded low power
variation like low-dropout regulator. Noisy power supply can
corrupt Memory data unintentionally. [15], [16]
USB Controller
The power requirement for the USB controller is 3.0V to
5.0V for the operating voltage and the current consumption
during full speed operation is typically 30 mA to 55 mA. However, the power for the USB controller is supplied by the PC
through the USB cable. In fact, when downloading music files
from a PC to the portable MP3 player via the USB cable, the
MP3 player will be powered by the PC. This is known as downstream power. [18], [19]
System Logic Interface
The system logic interface can be operating at 1.4V to 3.6V
with 3.3V as the typical operating voltage and the maximum
current consumption is about 50mA which depends on the
complexity of the system. [17]
Headphone Amplifier
Low voltage stereo headphone amplifiers which can deliver
10mW to 20mW power at a 16 W or 32 W load per channel are
usually used. These low voltage stereo amplifiers can be operated at 1.0V to 5.0V supply voltage and their operating current
is typically 1.0mA to 5.0 mA. However, some stereo DAC
devices have already built-in with stereo headphone amplifiers, as a result, extra stereo headphone amplifiers are not
required. [20], [21], [22]
International IC – China • Conference Proceedings 407
MP3 system power supplies solution
Two common power management solutions can be used to
power portable MP3 players, distributed power management
(DPM) and integrated power management (IPM). Distributed
power management is commonly used in 1st generation products for shortening new product’s time to market and higher
flexibility to changes in system design. Integrated power management is adopted for later product cost saving if product life
cycle permits.
Distributed Power Management
Distributed power management solution is the commonest form
adopted in most MP3 player design. It is based on the discrete
approach where semiconductor supplier offers a catalogue of
devices in tiny packages, such as SOT-23 and micro-8, to system design house for design solution. Series of devices like
DC-DC converters (step-up and step-down), low-dropout regulators (LDO), micro-reset, Op-amp, and EL driver.
Integrated Power Management
Integrated power management solution is aimed at reducing
board space and total system cost. System functions can be integrated as much as possible in a single IC package depended
on technology constraints.
For example, extensive logic functions can be integrated in
the power management IC with the mature BiCMOS technology. This benefits the system in two ways. Firstly, the power IC
will have a smoother interface with the microprocessor, such
that the direct firmware control adds intelligence to the end
product. Secondly, protective mechanism and error reporting
can be implemented within the IC.
Distributed Vs. Integrated
There is no specific rule to determine which is the best solution, although system design house often struggle for which
power management solution is the best. However, Table 2 illustrates some system factors to trade-off which system designer
can take it as a reference. One thing for certain in new product
development is time-to-market. The common approach is to
use off-the-shelf parts (DPM) to provide power management
solution to test the end product and its market, and migrate
to the IPM later.
Figure 3. A block diagram of MP3 Player Power Supplies Solution
Therefore, a high efficiency DC-DC converter which can
be operated from 0.9V to 3.0V supply voltage and generate a
3.3V output voltage with 200 mA output current should be sufficient as the main converter for a typical portable MP3 player
system. An example of the main converter using ON
Semiconductor’s NCP1410 is demonstrated in Figure 4.
Figure 4. An example of the main converter using NCP1410
The LCD panel should be supplied by another boost DCDC converter with output voltage ranging from 15V to 25V,
which is dependent of the LCD panel size, and output current
required is below 15 mA. An example of LCD bias converter
using ON Semiconductor’s NCP1403 is presented in Figure 5.
Figure 5. An example of LCD bias converter using NCP1403
Table 2. System factors to trade-off for DPM vs. IPM
An EL driver which generates a high AC voltage, typically
60Vp-p to 200Vp-p, from a 1.8V to 3V low DC voltage is required to drive the EL lamp to illuminate. An example of EL
driver application circuit is illustrated in Figure 6.
An Example of MP3 Power Management Solution
A typical MP3 system power management solution using DPM
is illustrated in Figure 3 below. As shown from the previous
section, MP3 player system employs 3.3V for system controller, MP3 decoder, system logic, Flash memory, stereo DAC,
and stereo headphone amplifiers; a 3.3V DC-DC voltage converter is therefore necessary. While the earlier models are powered by two size AA/AAA batteries, however, the new models
trends to be powered by a single size AA/AAA battery for
further reduction in product size.
Figure 6. An typical example of EL driver application circuit [23]
408 International IC – China • Conference Proceedings
Some supervisory functional blocks are usually utilized in
portable MP3 systems for more intelligent power management.
These supervisory functional blocks are power-on reset and lowbattery detection. The power-on reset block activates the startup sequence after the battery is being installed in the MP3 player
system. When the main converter output voltage reaches a certain preset level, the power-on signal will go high and wake up
the microcontroller after a user-defined time delay. The time
delay is adjustable by a external capacitor. Whereas, the lowbattery detection is implemented by comparing the battery voltage or the divided-down battery voltage with an internal reference voltage which is commonly 0.9V or 1.2V. If the battery
voltage falls below the user-defined operation limit, a low-battery warning signal will be issued to notify the microcontroller.
Some DC-DC converters are built-in with supervisory functions to simplify system design. The DC-DC converter shown
in Figure 4 is an example of this. Moreover, these supervisory
functions can also be accomplished easily by some separated
voltage detectors. An example of power-on reset and low-battery detection is shown in Figure 7.
Reference
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
Figure 7. An example of power-on reset and low-battery detection
implementation
17.
What is more, system designer should optimize the power
consumption by disabling some idle blocks in the system during different operating mode, such as play mode, record mode,
sleep mode, and low power stand-by mode. This can be done
by applying control signal from the microcontroller to the chip
enable pin or shutdown pin of the corresponding devices in
each functional block.
Conclusion
A brief introduction to MP3 player and MP3 audio file format
has been discussed. A concise MP3 player market overview
has been covered. Moreover, the overall electronic system of
MP3 player and power requirements of various components in
a MP3 player has also been presented and highlighted. Finally,
a distributed power management solution with examples of the
main DC-DC converter, LCD bias converter, EL driver, and
supervisory functional blocks, like power-on reset and low-battery detection, has been presented. The readers should have a
better understanding of the MP3 file format, the portable MP3
player system architecture and power requirements, and the
power management solution of portable MP3 player. A distributed power management solution presented is for reducing the
time to market and more adaptive to the fast changing market
requirements.
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International IC – China • Conference Proceedings 409
Authors’ contact details
Guy F.K. Cheung
ON Semiconductor
18th Floor, Tower II
Grand Central Plaza
Shatin, New Territories, Hong Kong
Phone: (852) 2689 0245
Fax: (852) 2689 0095
E-mail: [email protected]
Tze-kau Man
ON Semiconductor
18th Floor, Tower II
Grand Central Plaza
Shatin, New Territories, Hong Kong
Phone: (852) 2689 0229
Fax: (852) 2689 0095
Email: [email protected]
410 International IC – China • Conference Proceedings
Lawrence H.S. Ling
ON Semiconductor
18th Floor, Tower II
Grand Central Plaza
Shatin, New Territories, Hong Kong
Phone: (852) 2689 0249
Fax: (852) 2689 0095
E-mail: [email protected]
Ho, C.O. Indy
ON Semiconductor
18th Floor, Tower II
Grand Central Plaza
Shatin, New Territories, Hong Kong
Phone: (852) 2689 0227
Fax: (852) 2689 0095
E-mail: [email protected]