Manfred Pauritsch, University of Applied Sciences
Replacing existing benchtop equipment with a fully automatic measurement system to accurately characterize analog-to-digital converters (ADCs) to improve quality, reduce costs, and shorten test development time.
Creating a measurement system based on PXI components capable of performing a variety of measurements including integral nonlinearity (INL), differential nonlinearity (DNL), and signal-to-noise-distortion ratio (SINAD) to characterize ADCs from the Standard Linear (SLI) product line of austriamicrosystems.
Manfred Pauritsch - University of Applied Sciences
Wolfgang Koren - austriamicrosystems
Before we release our integrated circuits into full production, we have to thoroughly test their performance over a given temperature range using an adequate amount of samples. By implementing this process, we can deliver high-quality parts to our customers.
austriamicrosystems is a global leader in the design and manufacture of high performance analog integrated circuits (ICs). We leverage our expertise in providing low power and high accuracy best-in-class products for communications, industrial, medical, and automotive markets worldwide. We develop and produce industry-leading analog semiconductors, including high performance standard products and customized solutions.
In cooperation with the Automation Systems Department at the University of Applied Sciences in Graz, Austria, we developed a fully automatic measurement system based on PXI, which supports the accurate characterization of ADCs. We used this measurement system to characterize ADCs from the Standard Linear (SLI) product line of austriamicrosystems.
Our ADC portfolio of standard products contains 10- and 12-bit converters that can sample at up to 400 kS/s with very low power consumption.
Each product uses either a serial or parallel digital connection to a microcontroller. Our ADCs are comprised of single-ended as well as true-differential products with up to eight channels.
We divided the ADC measurements into nine different groups that cover all of the parameters for the chip. In addition to the respective data sheet parameters, we characterized additional specifications that are correlated with the converter quality and provide valuable findings for further development. The test groups for the ADC include the following:
1) Dynamic Performance
a. SINAD - Signal-to-noise and distortion ratio
b. SNR - Signal-to-noise ratio
c. THD - Total harmonic distortion
d. EOB - Effective number of bits (EOB)
e. PHSN - Peak harmonic or spurious noise (PHSN)
2) Statistical Performance
a. INL - Integral nonlinearity
b. DNL - Differential nonlinearity
3) Offset Performance (Offsets, Gains)
4) Intermodulation Distortion Performance
a. IMD - Intermodulation distortion
b. ISO – Isolation
c. Second/Third Order Terms
5) Logic Inputs (Input High/Low Voltages)
6) Internal Performance (Bandgap, VBG, TK, IREF, VREF)
7) Energy Performance (Current consumption, VREF)
9) Resistance and Capacity Performance (Analog/Logical Input Capacitance, Input Impedance)
By automating the measurement sequence, we characterized a large number of converters from ongoing production to obtain a coherent statistical picture of the respective parameters via the production tolerances.
We chose the components for the measurement system with regard to their measurement precision. We wanted the final system to be completely automated with synchronized generation and acquisition signals. The core of the system is an NI PXI chassis that contains an NI PXI-5422 arbitrary waveform generator, an NI PXI-6552 digital waveform generator/analyzer, an NI PXI-4130 source measure unit, an NI PXI-4110 programmable power supply, and an NI PXI-6259 multifunction data acquisition (DAQ) module. The following describes how each of these instruments were used in our system.
The PXI-5422 module is a 16-bit, 200 MS/s arbitrary waveform generator (ARB) used for time and frequency domain measurements requiring high bandwidth. We used the ARB to send a variety of analog patterns to the ADC for INL, DNL, SNR, and a number of other specifications to characterize its performance. The synchronization provided by PXI allowed us to operate the ARB as a phase-coherent multi-channel generator.
The PXI-6552 module is a 100 MHz digital waveform generator/analyzer that provides 20 channels of DIO with programmable voltage levels for VOH, VOL, VIH, and VIL. The digital generator/analyzer captured the output from the ADC and was synchronized with the ARB to create a tightly correlated mixed-signal system.
The PXI-4130 four quadrant source measure unit (SMU) and PXI-4110 Programmable Power Supply were used for parametric measurements on the ADC requiring up to 1 nA of current resolution. We used the power supply to provide power to the ADC and monitor supply current, while the SMU was used to characterize high and low voltage levels of digital inputs, or to source/sink current on digital outputs to simulate a bus load that would be driven by the ADC.
The PXI-6259 is a mixed-signal, high-speed data acquisition module with a variety of analog and digital I/O capabilities. We used this module to capture standard housekeeping information and control internal switches on the analysis board to select different test modes on the ADC.
The measuring station also consists of a programmable power supply, three multimeters, one 100 MHz oscilloscope, one 400 MHz digitizing oscilloscope, and one external function/arbitrary waveform generator. We used these instruments in conjunction with a temperature chamber or thermostream for temperature characterization to conduct measurements in the entire specified temperature range of the ADC.
The University of Applied Sciences developed an analysis board shown in Figure 3 with an intelligent design to support an almost fully automated evaluation of the entire ADC. To automate the measurements, we switched analog signals from the arbitrary waveform generator directly over a precision relay to the respective inputs of the ADC. The response of the ADC is measured using the digital waveform analyzer. We also used the high-speed digital instrument to operate the digital control lines for the ADC, and synchronized both the arbitrary waveform generator and the high-speed digital instruments using NI T-Clock, which guaranteed fast and optimized measurement cycles.
We developed the complete acquisition and control system using NI LabVIEW. LabVIEW VIs control the measurement system, which we divided into subVIs for various routines including group-pattern generation, digital acquisition, and analog signal generation/acquisition. Each subVI controls the respective tasks for a routine and any special parameters that may be needed. The division of each routine into subVIs combined with a pattern-oriented structure provides high flexibility and guarantees reusability when testing new products.
Once the LabVIEW execution completed, the test data is transferred to NI DIAdem software which was used to create a fully automated measurement log.
The image on the left side of Figure 4 shows a log generated from NI DIAdem summarizing dynamic performance values for SINAD, SNR, THD, EOB, and PHSN. The image on the right side of Figure 4 is a log generated showing the statistical performance comprised of INL and DNL.
Our test system demonstrates how a well-designed measurement system using off-the-shelf hardware and software components with PXI can considerably improve the quality of semiconductor characterization. Integrated systems such as PXI offer tightly correlated generation and acquisition signals through clock synchronization for characterization of our ADCs. Using PXI, we greatly improved the quality of our ADC characterization tests and reduced test costs by saving valuable test development time. The system has become the standard ADC test system for all characterization engineers at austriamicrosystems. We saved important and expensive analysis time using this approach and, due to the high-reusability factor of the system hardware and software, we will also be able to realize future projects faster.
University of Applied Sciences