Synchronizing handshaking between data converters and high speed digital data acquisition systems

October 30, 2013 //By Sudhansu Mishra
Synchronizing handshaking between data converters and high speed digital data acquisition systems
Sudhansu Mishra looks at data converters in SOCs using data acquisition systems (Logic analyzers or High speed digital input output [HSDIO] cards) and proposes a novel method to synchronize capture data. The article also discusses the challenges of other methods of data acquisition that cannot be used in high speed ADCs.

ADC characterization is a process that has evolved over decades with corresponding increases in complexity because of increasing speed of conversion and synchronization between converters, sources and acquisition systems.

Introduction:

Data converter (ADC) characterization is a requirement that has grown sophisticated over the years as more and more high speed converters are populating the market. Characterization is a precise process that requires stable data acquisition systems to be fully synchronized with the data converter without introducing any artifacts.

Static and Dynamic analyses of data converters require capturing the N-bit data word, from the data converter, over several thousand samples for post processing and analysis.  Post processing is required because most data converters like SAR don’t have an on board hardware for FFT (harmonic analysis, noise analysis) and memory for code comparison (Gain, offset errors etc.).

For an N bit ADC characterization it is required to capture minimum 2N+4 samples and post process them to know the performance of the ADC. After each conversion, the ADC stores the converted data in the result register. This data needs to be stored somewhere, or else it would be over written after the next conversion.

Fundamentally there could be only two ways to capture the conversion data:

  1. Data is transferred to the external world after every conversion which we call “Real time data capture.
  2. Data is first stored in the SRAM and later it is transferred to the external world which we call “Data capture through SRAM”

Both above methods have pros and cons which we will be discussing in the subsequent sections.

ADC conversion process:

Before we go into details about the two methods mentioned above, let’s see the basic step for the ADC conversion process. Please note – below steps are specific to SAR ADC’s but can be generalized to other type of ADC’s also.

Figure 1: Flow chart showing basic ADC conversion process

Data acquisition systems and ADC:

To capture digital

Design category: 

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