Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 21 - Trend Removal (Part 1)

When you retrieve measured waveforms from a DUT ADC or a digitizer, you may have ex-perienced to see ugly DC offset drift and to have hard time to get a flat noise floor in the spectrum. It could often occur when DC blocking capacitors are provided in the test signal path in a DUT board. In the articles of this month and next month, how we could cope with such situations is discussed. PDF, 994 KB. .

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 20 - Effect of Jitters in Sampling Clock and Test Signal

Recently more and more ADC and DAC are getting employed in high frequency applications such as telecommunication devices and digital consumer audio/video devices. The signal fre-quency is getting so high that the converter devices need high quality sampling clocks and test signals. In this issue, let’s look at the effect of jitters in the sampling clock and the test signal. PDF, 353 KB

Frequency/Phase Movement Analysis by Orthogonal Demodulation: Part 1- Basic Theory and PLL Lock-in Trend Analysis by Waveform Digitizer

In mixed signal system-on-a-chip (SOC) testing, there are many needs to measure phase and frequency change of signals. For instance, in a PLL circuitry, the lock-in time is one of the most typical test items. In a read/write channel device for hard disc drives, small pulse shifts for write pre-compensation are tested. Waveform digitizers or samplers that are typical mixed signal analog equipments can measure such changing frequency/phase with sophisticated digital signal processing. The sampled data is processed with the orthogonal demodulation method (ODM), which can extract the instantaneous phase of the test signal and analyze the frequency/phase changing trend. Swept frequencies, phase-shifted clocks, shifted pulses or edges are analyzed. PDF, 1.4 MB.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 19 - ADC Histogram Linearity – Programming

This issue is a follow-up for the last month’s article, where novel linearity calculation equa-tions of the ADC histogram methods are described step by step. There are two stimuli – ramp and sine waveforms. Let’s look at the practical program coding in this issue. A dedicated API will be available in the SmarTest soon; however, if you would need more information such as a histogram for your debug/analysis purpose, you may want to deploy the example codes in the issue. PDF, 648 KB

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 18 - Histogram Method in ADC Linearity Test

Linearity is the most important specification of A/D converters (ADC). There are several methods available to test linearity of ADC. Histogram analysis is quite simple and easy to apply so that it is one of the most typical test methodologies. It may be called as a code density test. Ramp histogram and sine histogram tests have been used for a long time; however, linearity calculation equations for ramp/sine histogram are not well organized. In this document, his-togram methods are discussed in detail, focusing on a terminal based (end-point) transfer function, easy-to-use equations are introduced with using cumulative distribution function for sine histogram. The method using this equation is free from overload level and offset of test signal sine so that test procedure is simple and fast in both hardware-wise and software-wise. PDF, 164 KB

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 17 - Another Method in Signal/Noise Calculation

In some cases, calculating Signal to Noise Ratio using FFT is not possible or gives inaccurate results. This article discusses calculating Signal to Noise ratio in the time domain. The strategy is to separate the signal from the noise. Estimation of the fundamental signal is the key. PDF, 690 KB.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 16 – Moving Average

When you measure a signal and it looks noisy, you may want to make it smooth with the moving average. Moving average operation is actually very similar to FIR convolution so that it behaves like a low pass filter. In this article, the frequency characteristics of the moving average and related comb filters are discussed. A different taste of filtering from the FIR convolution is discussed here. PDF, 705 KB.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 15 – Filtering in Frequency Domain

In the June issue of go/semi, the keys to successful (Inverse Fast Fourier Transform) IFFT were discussed. In this issue we will look at one of the typical applications of IFFT. It is type of filter processing in the frequency domain. A waveform refining procedure is also discussed. PDF, 369 KB.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 14 – FIR Filter

FIR or finite impulse response is a time domain waveform which can be utilized for digital filtering with convolution mathematics. Filtering by the FFT-IFFT method discussed in a previous article has a restriction that the waveform length should be 2n points. Convolution does not have such restriction so that, if the number of data is not 2n, FIR filtering can be useful. In this article, you will see how to create a FIR simply and how to play filtering. More over FIR can be generated with utilizing IFFT. So this is one of the practical applications of IFFT. In order to check the frequency response, a multi-tone signal is used. You can generate a time-domain waveform by using IFFT in the frequency domain. It is described as an example too. In this article you will see two practical applications of IFFT. PDF, 1.8 MB.

RF Lecture Series - Modulation Fundamentals - Introduction to WCDMA

Wideband Code Division Multiple Access (WCDMA) is a third generation (3G) mobile communications interface. WCDMA dynamically allocates the channel to optimize data rates for the user load and environment. The article provides an overview of WCDMA modulation fundamentals including an overview of the Transport and Physical channels. Composite and QPSK Error Vector Magnitude (EVM) test requirements High Speed Packet Access (HSPA) testing are detailed. PDF, 384 KB.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 13 – Inverse FFT

FFT is the fast version of DFT and is the most useful and powerful tool in mixed signal tests. DFT and FFT were discussed in previous newsletter articles. Inverse FFT(IFFT) is the opposite operation of FFT. IFFT processes frequency domain spectrum into time domain waveform. IFFT is not as popular as FFT, however, it can be utilized to manipulate waveform data such as filtering, compensation, modulation and so forth. In this article, you will learn how to perform IFFT correctly. PDF, 328 KB

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 12 - Spectrum Estimation

In a previous go/semi article, windowing was discussed for coping with the situation that the measurement period does not contain an integer number of signal cycles. Two windows were introduced. FLAT_TOP window is useful and accurate in regular amplitude estimation without any special data manipulation. HANNING window may be less popular than FLAT_TOP in general. However, there is a remarkably marvelous application available with HANNING window. It was developed and reported by Dr. Tabei and Dr. Ueda in 1987. In this article, the author is going to digest the core part of the original paper, and show how to deploy it in a practical procedure. PDF, 1 MB

RF Lecture Series: Modulation Fundamentals - Introduction to TD-SCDMA

TD-SCDMA, or Time Division-Synchronous Code Division Multiple Access, is a 3G mobile telecommunications standard, being developed initially for People’s Republic of China. It has been adopted by ITU and by 3GPP as part of UMTS Release 4, and is hence becoming a global standard. At the point of writing, this standard is relatively new. This paper intends to provide the basis of demodulating TD-SCDMA waveform for a successful EVM testing. It will first discuss the basics of the TD-SCDMA modulation to give the reader an idea of how the waveforms are created before dwelling on the mechanics of demodulating the signal. 134 KB.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 11 - Windowing

The coherent condition was discussed in the seventh article of this series. It is the most important test condition in DSP-based testing. You must set up your test condition to make it strictly coherent. However, if for some reason you have a situation that you cannot make strictly coherent, there is a workaround technique. It is called“windowing,” which is the theme of this issue.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 9 - Under Sampling 2

In last month's issue of go/semi, the fundamentals of under-sampling were discussed. In this and subsequent issues, practical conditioning strategy of under-sampling is discussed in various applications. There are two types of analysis methods available. One is waveform analysis in the time domain, and the other is spectrum analysis in the frequency domain. In this paper waveform analysis in the time domain is discussed.

RF Lecture Series: Modulation Fundamentals 6 - Introduction to WiMedia Alliance UWB (Wireless USB) 802.15.3a Modulation Standard

In this paper, the basics of the IEEE 802.15.3a indoor operation standard will be described. The motivations for its use, and architectural comparisons to narrow band transceivers will be considered. Then, limitations to its omnipresence are visited, and finally, a thorough overview of the UWB modulation fundamentals is described.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 8 - Under Sampling

You may remember one of the fundamental theories discussed in the first article -- "Nyquist Theory." If your signal is band-limited, when you would sample it with the frequency more than twice the maximum frequency of the band, all characteristic information of the signal is stored in the discrete time data stream. In other words, if the sampling frequency is lower than twice the bandwidth, something would be lost. This condition is called "under-sampling," which is the theme of this article.

RF Lecture Series: Modulation Fundamentals 4 - Introduction to 802.11n Modulation Standard

The IEEE 802.11n is a wireless local area network specification. The objective of IEEE 802.11n specification is to increase the throughput beyond 100 Mbps as well as extending the effective range from previous 802.11a/b/g standards. At the time of writing, 802.11n itself has not been ratified by IEEE. However many aspect of the protocols have been set.

The purpose of this article is to introduce the basics of the 802.11n standard, and give some of the fundamentals about how to perform some advanced 802.11n tests on Verigy's V93000. This article describes the fundamentals of the 802.11n frame structure, then goes on to discuss the spectrum, and spectral mask requirements. Finally, the EVM test for the 802.11n standard on the V93000 is described.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 7 - Coherent Condition

In mixed signal testers or the DSP-based testing, test sgnal waveforms are digitized with a waveform digitizer/sampler or an A/D converter, and the captured signal is processed with DFT/FFT basically, and a frequency spectrum is created to point out the particular signal components. DFT/FFT is the main tool to analyze signals. The most important factor in the DSP-based testing is coherent condition, which is the theme of this article.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 6 - Spectrum Analysis -- FFT

Test/application engineers in the mixed signal field should have thorough knowledge about DSP-based testing. FFT (Fast Fourier Transform) is the most powerful tool here. This corner will deliver a series of fundamental knowledge of DSP-based testing, especially FFT and its related topics. It will help test/application engineers comprehend what the DSP-based testing is and assorted techniques.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 5 - Spectrum Analysis -- DFT

Test/application engineers in the mixed signal field should have thorough knowledge about DSP-based testing. FFT (Fast Fourier Transform) is the most powerful tool here. This article continues the series of fundamental knowledge of DSP-based testing, covering FFT and its related topics. It will help test/application engineers comprehend what the DSP-based testing is and assorted techniques.

RF Lecture Series: Modulation Fundamentals 3 - 802.11b/a/g Modulation Standard

WLAN standards have appeared as a result of mobile computer users who need to remain connected to the network. As an extension to Fixed-LAN networks, WLAN needs to be compatible to the previous standard. The fact that now the radio channel is used, adds lots of complexity to the standard because of the RF error-prone nature of this medium. To avoid any kind of interference, to avoid collisions or to assure security, many challenging changes have been implemented and tests have been defined to enable the manufacturability of WLAN devices. This article will focus on the standards 802.11a/b/g.

Mixed Signal Lecture Series: DSP-Based Testing Fundamentals 4

Multi-tone is a popular stimulus signal in mixed signal tests. By using a multi-tone you can capture gain and phase information at multiple frequency points with a single measurement so that it is very effective in frequency response analyses. As discussed in the last newsletter, when a multi-tone is programmed and generated by a DAC, it has a gain shaping of SINC function. In this issue, let’s look at the waveform and think of the point of appropriate multi-tone signal generation.

Modulation Fundamentals 2 - Bluetooth EDR Demodulation on the V93000

Although Bluetooth has been around for years and was thought to be mature in the automated test equipment (ATE) world, new test requirements have arisen. In 2005, Bluetooth EDR (Enhanced Data Rate) v2.0 was introduced, adding increased data throughput over first-generation Bluetooth (v1.0 and v1.2). Although it has kept the occupied bandwidth the same, this additional data rate has introduced many new test requirements that need to be explained and understood.

Mixed-signal Lecture Series: DSP-Based Testing Fundamentals 3

When a DA converter (DAC) is stimulated a certain code, the DAC generates a DC voltage specified and holds its level until the next code is fed in the DAC. Therefore the waveform out of a DAC theoretically looks like staircase. In this issue let’s look at the DAC output waveform.

Mixed-signal Lecture Series: DSP-Based Testing Fundamentals 2 - Waveform Generation

ADC and DAC are the most typical mixed signal devices. In mixed signal testing, analog stimulus signal is generated by an arbitrary waveform generator (AWG) which employs a D/A converter inside, and analog signal is measured by a digitizer or a sampler which employs an A/D converter inside. The stimulus signal is created with mathematical method, and the measured signal is processed with mathematical method, extracting various parameters. It is based on digital signal processing (DSP) so that our test methodologies are often called DSP-based testing.

Modulation Fundamentals 1 - Modulation and EVM Analysis

Modulation analysis is increasingly integral to the test strategies of integrated RF SOC transceivers. The trend is that as the industry gets closer to a single-chip cell phone, more and more mission mode tests need to be performed on the transceivers to make sure that all components of the radio are working together flawlessly. In RF SOC, nothing represents mission mode test better than error vector magnitude (EVM). An acceptable EVM measurement for a complex modulation format implies that a whole host of transmitter or receiver components are within specification.

DSP-Based Testing – Fundamentals

In DSP-based ATE, analog signals are generated by arbitrary waveform generators (AWG) which contain D/A converters (DAC) inside, and analog signals are analyzed by digitizers or samplers which contain A/D converters (ADC) inside. DAC and ADC are also typical devices under test for mixed signal ATE. Read entire article.