The Digital Influence on Analog Technologies

In the midst of a digital era where information is easily accessible through digital sources, the physical world still remains almost exclusively analog. From wireless broadcasts to wired temperature measurements, analog technologies are as important today as they were 20 years ago. However, digital technologies that complement analog technologies have significantly changed over this same time period. Processing speeds have increased by three orders of magnitude, the Internet has changed the way people obtain information, and PC bus bandwidth has experienced a 500 times improvement. The overall trend shows that digital technology is faster, and engineers are more efficient because of it. How do analog technologies keep up with a faster world where information is quickly crunched and Gigabyte hard drives fill in seconds? By integrating new digital technologies, analog measurements have evolved over the past several years. Six digital technologies that have improved analog measurements include higher-performance analog-to-digital converters (ADCs), digital isolators, reconfigurable field-programmable gate arrays (FPGAs), next-generation PC buses, lower-power MOSFETs, and high-speed digital downconverters.

Figure 1. With new analog measurement systems, you can use a reconfigurable FPGA as the controller and higher-performance ADCs and digital isolation integrated with the I/O.

 

Analog-to-Digital Converter Trends

When it comes to digitizing a real-world signal into its binary representation, it is obvious that ADC quality has a direct effect on measurement accuracy. ADCs have several associated parameters and specifications, but at the highest level, an ADC is characterized by its resolution and sampling speeds. Higher-resolution ADCs can measure smaller signals. Faster sampling speeds can capture more of the original analog signal in the digital representation.

Over the past decade, increased innovation in the electronic component industry has resulted in decreased ADC component costs while simultaneously increasing performance. This trend led to higher-performing devices at prices often less than that of legacy devices. Today for example, high-performance NI M and S Series data acquisition (DAQ) devices feature one or more ADCs, 16-bit or higher resolutions, and 1 MS/s or faster sampling rates at prices less than that of the first PC-based data acquisition devices of the late 1980s, which featured a single 12-bit, 10 kS/s ADC. Sampling speeds of commercially available ADCs also have significantly increased over the decades. For example, the new National Instruments PXI-5105 high-speed digitizer packs in eight 12-bit ADCs sampling at 60 MS/s simultaneously, and the National Instruments PXI-5152 digitizes signals as fast as 2 GS/s. By designing around new ADC technologies, NI continually improves analog measurement capabilities with lower-cost, higher-performance devices.

Figure 2. ADC prices have decreased over the past two decades, while performance has simultaneously increased. (Graph Source: National Instruments and a leading ADC supplier)

Learn more about NI M Series DAQ devices  and new high-speed digitizers.

 

Digital Isolation Protects Investments and Increases Accuracy

Isolation adds safety to measurement systems by electrically separating different parts of the data acquisition circuitry. Isolation prevents hazardous voltages from damaging the measurement device, other electrical equipment, and you as the human operator. Traditional isolation schemes use analog isolation components based on amplifiers or transformers. Analog isolation technologies are nonlinear; susceptible to drift; and expensive in regards to power consumption, physical space, and price. Analog measurement systems often omit isolation due to the drawbacks of analog isolators for faster, more-accurate, and less-costly systems.

To eliminate these limitations, silicon vendors introduced new isolation components that use digital designs based on transistor-level transformers. Digital isolation provides faster, more-accurate, higher-density, and lower-cost solutions, ensuring the safety of measurement systems. In addition to the increased safety provided by devices with digital isolation technologies, isolation removes ground loops, reduces system noise, and rejects common- mode voltages. New NI devices – including Industrial M and S Series DAQ devices as well as C Series modules used in NI CompactDAQ and NI CompactRIO – use digital isolation to protect investments and increase measurement accuracy.

Figure 3. NI C Series modules protect measurement systems by integrating digital isolation to separate hazardous signals from the system controller and bus.

Read a white paper on how isolation technologies improve measurement reliability.

Table 1. NI M and S Series DAQ devices with isolation offer ±20 mA analog I/O and 24 V digital I/O.

 

“Custom” Off-the-Shelf Hardware with FPGA Technologies

It seems oxymoronic to mention custom hardware in the same context as commercial technologies, but it is now possible by using FPGAs in combination with analog designs. Previously, if a commercially available system was incapable of performing particular measurement types, you often had nowhere to turn except to a custom solution. However, by replacing the onboard vendor-defined system timing controller, which controls sampling rates, triggering, and bus transfer, with a reconfigurable FPGA, you now can create custom hardware by redefining the way the hardware operates. With FPGA-based designs, including NI R Series intelligent DAQ devices and CompactRIO, you can create custom sampling, triggering, and onboard processing with 25 ns resolution and 40 MHz loop rates. To aid in productivity, you are not required to learn VHDL or other low-level design languages when using National Instruments FPGA-based designs. Instead, with the NI LabVIEW FPGA Module, you can design custom hardware without leaving the graphical programming environment.

 

Next-Generation PC Buses Expand Instrument Capabilities

With PC-based analog measurement devices now capable of acquiring data at rates over 1 GB/s, designers must come up with innovative techniques to transfer larger amounts of data to the PC for processing. These transfers are handled by the data bus connecting the device to PC memory. However, the rate at which data transfers occur is often the bottleneck in measurements, and is the primary reason that many instruments have incorporated expensive onboard memory.

PCI Express, the next-generation PC bus, addresses the growing demand for bandwidth. Originally designed to enable high-speed audio and video streaming, PCI Express is also being used to improve the data rate from measurement devices to PC memory by up to 30 times versus the traditional PCI bus used on desktops for the past 10 years. PXI Express, the last addition to the PXI platform, combines PCI Express signaling into the PXI standard, increasing backplane bandwidth from 132 MB/s to 6 GB/s. While both PCI Express and PXI Express increase bandwidth and provide dedicated bandwidth per module slots, the new bus technologies protect current investments by providing backward compatibility with existing software applications.

View a list of PCI Express and PXI Express products from National Instruments.

Figure 4. PCI Express provides increased bandwidth over other PC buses and dedicates bandwidth per device.

 

Low-Power MOSFETs Used in High-Power Control

Gone are the days when large, bulky instruments were required for motor drives and power supplies. Through the use of insulated gate bipolar transistors (IGBTs) and low-power MOSFETs, motors and their electrical power supplies can now be built compact, precise, and high-power. These technologies control kilowatts almost as efficiently as logic semiconductors control the picowatts in logic bits. NI uses low-power MOSFETs and IGBTs in the new NI CompactRIO power drive module and PXI programmable power supply.

Download specifications for the new drive module for CompactRIO  and the new programmable DC power supply.

Figure 5. The NI PXI-4110 DC power supply provides three programmable outputs, each capable of delivering up to 1 A current drive.

 

RF/IF Digitization with Digital Downconverters

Using onboard signal processing (OSP), IF digitizers and vector signal analyzers can continuously acquire up to 20 MHz of the frequency domain. OSP implements a technique called digital downconversion (DDC), which reduces the acquired data from an entire IF waveform to just the baseband IQ data. Without doing this, it’s impossible to stream the amount of data acquired from an IF signal across standard PC buses. Once the downconversion process shifts the signal of interest to baseband, decimation of the signal takes place using an onboard FPGA to lower the effective sampling rate and the amount of data to be transferred to PC memory for processing. The new NI 5142 digitizers with OSP and the NI 5661 RF vector signal analyzers all use an onboard DDC to accomplish RF/IF streaming applications.

Read a white paper on how to use digital downconverters for high-speed RF/IF streaming.

 

Improving Analog Measurements with Digital Technologies

You use measurements to help pass or fail units under test, repair corrupted signals, and tell you what exists beyond what the eye can see. Today, the measurements you make demand higher speeds and higher accuracy, the enterprise demands increased safety, system requirements demand customization, and the economy demands lower prices. Through the use of commercial technologies, National Instruments extends the capabilities of measurement hardware by leveraging new ADCs, digital isolation technologies, and reconfigurable FPGAs. It is clear that today and in the future, digital technologies will continue to extend the capabilities of analog measurement.

 

 Jared Aho

Data Acquisition Product Manager

 

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