 Application Note
Digital Audio Design Validation and Debugging Using PGY-I2C
Debug the toughest I2S challenges, from Protocol Layer to PHY Layer to
Audio Content
Introduction
Today’s digital systems – from the Digital TV in the living room to the complex switching
elements in an IPTV network – are driving convergence on many fronts. Quality of
Experience is taking centre-stage. Audio requirements in Computers, Mobile Handsets and
Home Automation products have changed dramatically. Audio content to and from the
processors is increasingly becoming digital data.
Engineers validating hardware and firmware for I2S, often need to cross-examine the
protocol layer, the PHY layer and the audio content. These design scenarios have intensified
the need for one tool that spans across from Protocol layer to the PHY layer to Audio
Analysis.
This application note discusses a versatile tool that enables design and validation engineers
to efficiently, and effectively, debug the toughest I2S challenges using the PGY-I2S
application software. The software runs on Tektronix’ windows-based high-bandwidth
oscilloscope used in the validation of high-speed Serial Data technologies.
About I2S Standard
The digital audio signals in most systems are processed by a number of devices, such as
ADCs, DACs, DSPs, Digital I/O interfaces and many more. In order to enhance the flexibility
and interoperability, it is critical to have standardized communication structures, for both
the equipment and the silicon developers.
Inter-IC Sound (I2S) bus – a serial link, is developed specially for digital audio. The bus
handles only audio data through a simple, 3-line serial bus consisting of:
Continuous Serial Clock (SCK)
Word Select (WS)
Serial Data (SD)
The Clock
The transmitter and receiver have the same clock signal for data transmission. Typically, the
transmitter acts as the master, and generates the bit clock, word-select signal and data. The
slave derives its internal clock signal from an external clock input. In complex systems having
several transmitters and receivers, a system master controls digital audio data-flow
between various ICs.
 Application Note
For data and word-select inputs, the external to internal clock delay is of minor
consequence because it only lengthens the effective set-up time. The major part of the time
margin is set to accommodate the difference between the propagation delay of the
transmitter, and the time required to set up the receiver.
All timing requirements are specified relative to the clock period or to the minimum allowed
clock period of a device. Thus, higher data rates can be used in the future.
Word Select
The Word Select(WS) line indicates the channel being transmitted:
• WS = 0; channel 1 (left).
• WS = 1; channel 2 (right).
In the slave, this signal is latched on to the leading edge of the clock signal. The WS line
changes one clock period before the MSB is transmitted. This allows the slave transmitter to
derive synchronous timing of the serial data that will be set up for the transmission.
Moreover, it enables the receiver to store the previous word and clear the input for the next
word.
Serial Data
I2S offers a very high degree of flexibility. The transmitter and receiver may have different
word lengths. Also, it is not necessary for the transmitter to know how many bits the
receiver can handle, nor does the receiver need to know how many bits are being
transmitted.
To enable this, the Serial Data is transmitted in two’s complement with the MSB first. The
MSB has a fixed position, whereas the position of the LSB depends on the word length.
When the system word length is greater than the transmitter word length, the word is
truncated (LSB set to ‘0’) for data transmission. If the receiver gets more bits than its word
length, the bits after the LSB are ignored. In case the receiver gets fewer bits than its word
length, the missing bits are set to zero internally.
The Challenges
Key performance of current generation digital Audio is measured based on the quality of
output audio, battery life, and portability. To achieve these performance factors, industry
converts the analog audio signal into digital to reduce affect of SNR and also to employ
multiple digital signal processing algorithms to create a compelling audio experience. To
enhance the battery life, designer’s pursuing VLSI/LSI designs based on power aware
technology. This technology changes the state of the different blocks within an IC
to on/off
These design practices throw up the following challenges to the designers.
Debugging the content of the Audio Serial buses.
Ensuring physical layer timing and compliance to standard.
 Application Note
Ensuring high level signal fidelity during the signal transformation from Analog to
Digital and vice versa.
Reducing the noise components generated due to mixed signal design and new
generation power-aware ICs.
Interoperability of different vendors Audio subsystems
Maximizing the design margins with low power and voltage.
Traditionally, engineers use multiple instruments such as Audio analyser for dealing with the
audio domain related challenges, logic analyser for dealing with the link layer challenges and
Oscilloscopes for dealing the signal integrity and timing challenges. Involving multiple
instruments adds additional complexity in the test setup.
Now a single tool has arrived to address all of the above challenges in the I2S design. PGYDAA I2S Digital Audio Analysis software along with the Tektronix Oscilloscope is a single tool
to cross-examine the protocol layer and the PHY layer while verifying the audio performance and
helps to address all the discussed challenges. This application note further explains the features of
the PGY DAA I2S Digital Audio Analysis Software
Tools for methodical debugging
Debugging starts from setting up the Oscilloscope
Every step in setting up the Oscilloscope is important in the debugging process because it
affects the reliability and accuracy of measurements and decoded information. The circuit
design and the bench validation engineers spend
considerable time in setting up the Oscilloscope
before they start characterizing their circuit
Setting up the Oscilloscope includes adjusting the
sampling rate, horizontal scale, horizontal trigger
position, vertical scale and vertical position etc.
Oscilloscope sampling rate plays an important role in the measurement and decoding the
analog signal. Theoretically to re-construct the waveform sampling rate should be at least
twice the frequency of the signal, but in digital domain the rise time of the signal plays a
major role in choosing the oscilloscope’s sampling rate.
Similarly oscilloscope’s vertical scale and its dynamic range play a major role in making
reliable measurements. Oscilloscope works with 8bit A/D converter. If the vertical
oscilloscope settings are not adjusted properly the oscilloscope’s full scale vertical dynamic
range will not be used. Thus higher quantization error results in poor measurement
reliability.
To make the engineers productive and reduce the errors in their debug process the I2S
Digital Audio Analysis solution provides oscilloscope setup assistance. Engineer needs to
provide the audio sample rate and the duration of the audio waveform which may be of
 Application Note
interest. The application sets the Oscilloscope’s vertical and horizontal parameters
automatically which helps the engineers to make a reliable measurement.
Physical layer and protocol triggering for efficient debug
Any circuit debug need a powerful triggering capability to detect the problem. Physical layer
designers often look for symptoms of timing violations on the I2S bus. I2S Digital audio
analysis software provides an efficient way of setting up the set-up and hold timings
between the data, clock and WS signals. It offers a comprehensive set of triggers to test and
debug the specified limits.
Digital designers debug the circuit based on the protocol data. This can be based on the
violation of the protocol or based on the value. I2S Digital audio analysis application
provides a facility to trigger the data based on the protocol value.
To ensure the interoperability between the different I2S transmitter and receiver it is
essential to meet all the standard requirements of the I2S specification, I2S Digital Audio
Analysis Solution helps the engineers to detect the problem in their circuit by offering a
comprehensive triggering support.
Penta Monitor for cross debug physical, protocol and Audio layer problems
Engineers designing hardware and firmware for I2S are constantly seeking ways to
differentiate their designs. Often times, they need one tool to cross-examine the protocol
layer and the PHY layer while verifying the audio performance.
The I2S Audio/Protocol Decode/PHY Layer Test
Software offers industry first and best Penta
Monitor is the unprecedented cross-layer
analysis tools and automation to improve quality
and productivity while managing your schedules.
PGY-I2S Penta Monitor consists of Spectrogram
Monitor, Audio Monitor, Signal Monitor,
Protocol Monitor and Eye diagram monitor. Each
monitor brings in a unique way of looking the
same I2S signal. Audio signals are not stationary it consists of multiple frequency component
at any given point in time. Spectrogram Monitor provides a three dimensional view of the
frequency components in the signal. Audio Monitor provides a insight into the transmitted
audio signal in time domain, Signal Monitor offers the physical layer signal along with the
overlaid decoded data along with the bus diagram. Protocol Monitor provides the protocol
listing along with the time with respect to the trigger position, and the Eye diagram monitor
provides a clear identification of overall system health and channel imperfections.
 Application Note
Further this app note discuss about how to use the Penta Monitor to debug various the I2S
Digital audio design problems.
Debugging the Physical layer timing problems
Interoperability is an important aspect of any standard. Interoperability means different in
each layer of the design. Since the I2S bus is serial in nature it is important to comply with
the setup and hold timings. The I2S standard defines the Clock to data, Clock to Word
select, and word select to data setup and hold time which are very vital for interoperability.
PGY-I2S offers an elegant single click to measure all the standard defined timing
measurements for each I2S data frame and provides the compliance results based on the
standard.
PGY-I2S analyzes each I2S data frame and compare with the standard there are very
minimal chances that the devices fail in the interoperability.
The real challenge of debug starts when one or more I2S physical layer signals fails to
comply to standard. In such cases, PGY-I2S offers a search capability to find the timing
violation frames. Based on the timing measurement search along with the and eye diagram
designers can effectively debug the timing violations.
Debugging the content of the digital audio
PGY-I2S Software Penta monitor offers multiple cross examine tools to debug the digital audio
content. Protocol monitor is the first place to look at the digital audio content which is transmitted.
Protocol monitor lists all the available I2S data with respect to the trigger position. Since the I2S
content is in 2’s complement format it will be difficult to interpret the data in the anlog data using 1s
and 0s.
While debugging the digital audio it is essential to know the list of I2S audio data transferred in the
I2S channel, PGY- I2S offers a Protocol Monitor which lists the I2S data along with the time stamp
with respect to trigger position. The protocol monitor
also supports multiple data format such as decimal,
hexadecimal, octal and 2s complement format. Time
stamp helps to identify the position of the data with
respect to trigger.
While debugging, if any mismatch in the data it needs
to be root caused to the physical layer, so any row
selection in the protocol view automatically synchronize
the data in the Signal Monitor, Audio monitor and
Spectrogram monitor as shown in the figure. The corresponding portion of the signal is also zoomed
in the Oscilloscope screen.
 Application Note
The comprehensive search provides an ability to search the data in the protocol listing, the list
search attribute includes equal to, less than, greater than within a range and out of range.
The protocol listing and search capabilities provided in the Penta Monitor helps to identify the I2S
audio content problem quickly and effectively.
Debugging the Audio problems
An important audio performance indicator in portable audio devices is the occurrence of the
strange, transient noises called “Click” and “Pop” heard when the unit is in operation.
In general digital circuits are designed in multiple functional blocks. To reduce power
consumption and extend the battery life often functional blocks are turned off or on
depending on the need. This functional design requirement magnifies the potential for the
“Click” and “Pop”.
An ideal audio component would exhibit no “Click” and “Pop”. In practice, however, all
audio amplifiers exhibit this to some degree due to turning on and off the digital circuits. To
identify the strange and transient noise such as “Click and “Pop”, PGY-I2S offers spectrum
monitor search capability.
Since the click and Pop are sudden change in frequency for a short period of time it will be
difficult to find them in the time domain. But PGY-I2S spectrogram monitor search helps to
quickly find the strange transient noises effectively. The click and pop can be identified using
the sudden change in a particular high frequency component and duration of the change.
The identified click and Pop portion will be displayed and highlighted in the spectrogram
monitor and Audio monitor.
After finding the transient noise it is important to identify the source of the noise. PGY-I2S
offers the 4th Channel to feed the suspicious noise source such as shutdown or enable
signals to the Penta monitor’s Signal Monitor to validate the “Pop” an “Click” with the
source. This process may need multiple iterations to identify the correct source of the
transient noise.
Similarly, PGY-I2S offers several audio search functionalities such as Glitch, silence, mute,
clip and bottom clip etc.
Transient-free audio performance is an important performance differentiator and a crucial
selling point for portable audio devices. I2S Digital audio analyzer’s spectrum monitor search
capabilities can help the audio circuit designer to identify the root cause the transient noises
such as “Click” and “Pop” and several other problems.
 Application Note
Testing and validating the I2S subsystem with industry’s standard patterns
Often times engineers test the I2S subsystem using few known patterns such as walking 1s,
walking 0s, content tone, constant values etc to validate the designs well before sending the
digital audio content. It is not easy to run thru’ the each data value and identify the failures
of these patterns. The pattern failure may not be clearly visible in the audio waveform or in
the eye diagram. PGY-I2S pattern search offers a unique pattern search technique which
helps to identify the patterns and search for failures. It also highlights the failures in the
protocol monitor and signal monitors. PGY-I2S pattern search capability is a handy tool
which helps the designers to use the standard patterns to validate their design.
Summary
PGY-I2S Electrical, Protocol and Audio Testing software answers to the need of a single
versatile tool to cross-examine the physical layer, Protocol layer and Audio Analysis. Industry
best and first Penta monitor helps the engineers to debug and root cause the complex I2S
design problems such as Pop, click and signal integrity challenges.
PGY-I2S I2S Audio / Protocol Decode / Electrical Test Software along with the Tektronix
DPO7000, DPO/MSO70000/B series oscilloscope offers comprehensive set of tools which
enables design and validation engineers efficiently, and effectively, debug toughest I 2S
challenges.