Digital Audio Design Validation and Debugging Using PGY-I2C Debug the toughest I 2 S 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 I 2 S, 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 I 2 S 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 I 2 S 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 (I 2 S) 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.
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 I 2 S 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.
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. PGY- DAA 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
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 I 2 S 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.
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.
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 4 th 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.
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 2 S challenges.