Pitfalls of Filtering Pulsed Signals

Waveform Woes

Filtering pulsed signals can be a tricky prospect. Using a recent customer problem as an example, Robert highlights various alternative approaches and describes the key concepts involved. Simulation results are provided to help readers understand what’s going on.

By Robert Lacoste

Welcome back to the Darker Side. A couple of months ago, one of our customers was having trouble with its project and called us for help. As is often the case, the problem was more a misunderstanding of the underlying concepts than any kind of hardware or software issues. We helped him, but because the same issue could jeopardize your own projects I thought it would be a nice topic for this column.

The Project

What is it about? Of course, I won’t be able share the details of our customer’s project, but I will describe a close example. Let’s imagine you need to build an ultrasonic ranging system. Just as bats do, you want to transmit short bursts of ultrasound, then listen for echoes. As you probably know, the time between transmission and reception divided by twice the speed of sound will give you the distance of the obstacle.

Moreover, the shift in frequency between transmitted and received bursts will give you the relative speed of this obstacle, thanks to the so-called Doppler shift. Ok, but how will you design such a ranging device? First, you’ll need to generate and transmit bursts of sine waves—also called tone bursts—with the proper ultrasonic frequency, say 40 kHz. That’s easy to do even with a pair of trusty NE555 chips or NAND gates, or maybe with a microcontroller if you prefer dealing code rather than a soldering iron. These bursts will need to be as short as possible—maybe 1 ms or so—because this will improve the distance resolution.

The transmit side is easy, but the receiver will be a little more complex. In real life, the received signal will have a very low amplitude and probably plenty of added noise. This is especially true if you consider that the Doppler shift could be significant, meaning with fast-moving objects. In that case you will not know the exact frequency of the burst you should detect.

Figure 1
Shown here is a basic ultrasonic meter. A narrow band-pass filter, tuned to the received frequency, allows you to reduce perturbations and noise. But does this work?

One possible architecture to avoid this problem, while minimizing noise, could be the one illustrated on Figure 1. First, do a spectrum analysis of the received signal. Because this signal contains noise plus the received ultrasonic echo, its frequency spectrum will show a peak at the frequency of the received ultrasonic carrier. Therefore, you can measure this actual reception frequency. Assume it is 40.5 kHz due to Doppler shift. You can use this information to tune a very selective band-pass filter, which will isolate the received ultrasonic burst from any other noise. Why not a 40.5 kHz +/-100 Hz filter? You will then recover a clean version of the received pulse and measure the time difference between transmission and reception with a detector and a time counter. Brilliant idea, isn’t it? If you agree, then please read on. This was the concept used by our customer, and unfortunately it doesn’t work! At least not as described. In this article I will explain why, using some easy to understand simulations and as little math as possible. So, don’t’ be afraid. Come with me to the Darker Side of pulsed signals.

Digital Version

Before going into the explanation, I need to present you an alternative version of this intended receiver. Because you are a reader of Circuit Cellar, you know that developing such a design would be far easier using digital signal processing than trying to build analog spectrum analyzers and precisely tuned filters. The digital equivalent of this receiver is illustrated on Figure 2. Just compare it with the former, you will find the same concepts.

Figure 2
Here’s a digital version of the same concept shown in Figure 1. All the yellow functions can be executed on a digital processor (fast microcontroller, digital signal processor, FPGA or anything else).

Here the received signal is preamplified and directly digitized with a properly selected analog-to-digital converter (ADC). Its frequency spectrum can then be calculated with a Fourier Transform, using the well-known Fast Fourier Transform (FFT) algorithm, for example. The frequency peak can then be searched into this spectrum. Then a narrow band-pass filter can be created and tuned to this frequency and the filtered signal can be calculated. …

Read the full article in the August 337 issue of Circuit Cellar

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MCUs Eye Closed-Loop Control Applications

Microchip Technology has introduced the new PIC18 Q10 and ATtiny1607 families, featuring multiple intelligent Core Independent Peripherals (CIPs) that simplify development and enable quick response time to system events. Advancements in the architecture of PIC and AVR 8-bit microcontrollers (MCUs) have optimized the devices for implementing closed-loop control, enabling systems to offload the Central Processing Unit (CPU) to manage more tasks and save power.

Well suited for applications that use closed-loop control, a key advantage of using the PIC18 Q10 and ATtiny1607 MCUs are the CIPs that independently manage tasks and reduce the amount of processing required from the CPU. System designers can also save time and simplify design efforts with the hardware-based CIPs, which significantly reduce the amount of software required to write and validate. Both families have features for functional safety and operate up to 5 V, increasing noise immunity and providing compatibility with the majority of analog output and digital sensors.

Offered in a compact 3 mm x 3 mm 20-pin QFN package, the new ATtiny1607 family is optimized for space-constrained closed-loop control systems such as handheld power tools and remote controls. In addition to the integrated high-speed Analog-to-Digital Converter (ADC) that provides faster conversion of analog signals resulting in deterministic system response, the devices provide improved oscillator accuracy, allowing designers to reduce external components and save costs.

Among CIPs in the PIC18 Q10 family are the Complementary Waveform Generator (CWG) peripheral, which simplifies complex switching designs, and an integrated Analog-to-Digital Converter with Computation (ADC2) that performs advanced calculations and filtering of data in hardware without any intervention from the core. CIPs such as these allow the CPU to execute more complex tasks, such as Human Machine Interface (HMI) controls, and remain in a low-power mode to conserve power until processing is required.

All PIC18 Q10 products are supported by MPLAB Code Configurator (MCC), a free software plug-in that provides a graphical interface to easily configure peripherals and functions. MCC is incorporated into Microchip’s downloadable MPLAB X Integrated Development Environment (IDE) and the cloud-based MPLAB Xpress IDE, eliminating the need to download software. The Curiosity High Pin Count (HPC) development board (DM164136), a fully-integrated, feature-rich rapid prototyping board, can also be used to start development with these MCUs.

Rapid prototyping with the ATtiny1607 family is supported by ATmega4809 Xplained Pro (ATmega4809-XPRO) evaluation kit. The USB-powered kit features touch buttons, LEDs and extension headers for quick setup as well as an on-board programmer/debugger that seamlessly integrates with the Atmel Studio 7 Integrated Development Environment (IDE) and Atmel START, a free online tool to configure peripherals and software that accelerates development.

The PIC18 Q10 and ATtiny1607 are available today for sampling and in volume production. Pricing for the PIC18 Q10 family starts at $0.77 each in 10,000-unit quantities, and pricing for the ATtiny1607 family starts at $0.56 each in 10,000-unit quantities.

Microchip Technology | www.microchip.com

MCU-Based Blood Pressure Monitoring Eval Kit

Renesas Electronics has announced an expansion of its healthcare solution lineup with the launch of a new blood pressure monitoring evaluation kit. The new blood pressure monitoring evaluation kit comprises hardware and software elements needed to jump start blood pressure measurement design. The kit includes a pressure sensor, arm cuff, pump, electronically controlled valve, LCD panel and a reference board. The reference board incorporates an RL78 MCU-based ASSP (application specific standard product) that includes analog functions required for blood pressure measurement. Reference software and graphical user interface (GUI) development tool are also part of the new evaluation kit. Using the new evaluation kit, system manufacturers can immediately begin their system evaluations and significantly reduce their development time.


The Internet of Things offers consumers connected tools with which to manage their personal healthcare more efficiently. For instance, blood pressure monitors are already popular personal medical devices and the market is expected to grow further as blood pressure monitoring functions are incorporated into wearable devices. The growth of this market offers new business opportunities, but can also be challenging, particularly for system manufacturers who are new to the connected healthcare device ecosystem and may not have the built-in application-specific expertise. Blood pressure measurement requires a specific expertise, including filtering functions for extracting the waveforms required for measurement, making it extremely time consuming to start studying this area from the very beginning.

Renesas has developed the new blood pressure monitoring evaluation kit to alleviate the development pain points, providing functions close to those used in actual blood pressure monitors thus accelerating blood pressure measurement system development.

Key features of the blood pressure monitoring evaluation kit:

The new blood pressure monitoring evaluation kit comprises hardware and software elements needed to jump start blood pressure measurement design, including:

  • A full range of hardware components, including a pressure sensor, arm cuff, pump, electronically controlled valve, LCD panel, and a reference board that incorporates the newly-developed RL78/H1D ASSP with the analog functions required for blood pressure measurement.
  • Reference software that provides the algorithms required for blood pressure measurement and that can be easily modified, as well as access to smartphone applications, and a graphical user interface (GUI) tool.
  • A Bluetooth Low Energy (BLE) module, which enables the measured data to be transmitted to a smartphone under the Continua standard blood pressure monitoring (BPM) profile is also provided in the new evaluation kit.

Development support with GUI tool, specialized for blood pressure measurement

  • The pressure sensor, pump, electronically controlled valve components, and pulse width modulation control can be set from the GUI tool. If the system structure is the same, the GUI tool can also be used for system evaluation of the actual application the system manufacturer is developing.
  • The IIR digital filter calculations required for extracting the pulse waveform from the cuff pressure output waveform during blood pressure measurement can also be simulated using the GUI tool. The digital filter constants calculated based on this simulation can be written from the GUI tool to the RL78/H1D firmware and verified in the actual application being developed. This significantly reduces the number of steps in the development process.

RL78/H1D ASSP with optimized analog functions for healthcare applications

  • The RL78/H1D is a new ASSP of the RL78 Family of MCU. The RL78/H1D, designed to control systems required for blood pressure measurement with a single chip. It incorporates rich analog functions including high-resolution delta sigma A/D converters, programmable gain instrumentation amplifiers, D/A converters, operational amplifiers, and other circuits required for blood pressure measurement, as well as timers for PWM (pulse-width modulation) control.
  • In addition to the delta sigma 24-bit A/D converters, the RL78/H1D also provides 10-bit sequential comparison A/D converters that operate asynchronously. This simplifies implementation of systems providing temperature measurement and battery voltage monitoring while measuring the blood pressure.
  • The Rich analog functions make the new ASSP ideal not only for blood pressure monitoring systems but also for a wide array healthcare application including biosensors.
  • Samples of the RL78/H1D ASSP are available now. Pricing varies depending on the memory capacity, package and number of pins. For example, the R5F11NMG 80-pin LQFP package type with 128 KB flash ROM capacity is priced at US$3.50. The R5F11NMG includes an LCD controller for arm- and wrist-type blood pressure monitors, and a 4mm x 4 mm miniature ball grid array (BGA) package for use in wearable devices.

Renesas plans to expand its range of solutions for the healthcare field and will continue to contribute to the realization of a safe and secure smart society, including the development of smart connected devices for the industrial and healthcare industries.

 

The new blood pressure monitoring evaluation kit is scheduled to be available for order from May 10 priced at $600 per unit.

Renesas Electronics | www.renesas.com

Gesture Recognition in a Boxing Glove

Sensors Packed in the Punch

Learn how these two Boston University graduate students built a gesture-detection wearable that acts as a building block for a larger fitness telemetry system. Using a Linux-based Gumstix Verdex, the wearable couples an inertial measurement unit with a pressure sensor embedded in a boxing glove.

By Blade Olson and Patrick Dillon

Diagnostic monitoring of physical activity is growing in demand for physical therapists, entertainment technologists, sports trainers and for postoperative monitoring with surgeons [1][2]. In response to the need for a low-cost, low-profile, versatile, extensible, wearable activity sensor, the Hit-Rec boxing sensor is a proof-of-concept device that demonstrates on-board gesture recognition and high-throughput data monitoring are possible on a wearable sensor that can withstand violent impacts. The Hit-Rec’s ability to gather raw sensor values and run calculations at a high frame rate make the Hit-Rec an ideal diagnostic device for physical therapists searching for slight perturbations across a user’s gestures in a single recording session or for looking at discrepancies between the ideal motions of a healthy individual and the user’s current motions. The following sections will describe the implementation of a prototype for the Hit-Rec using a boxing glove (See Lead Photo Above).

SYSTEM OVERVIEW

The Hit-Rec sensor incorporates a Gumstix Verdex Pro running Linux, a 9-DoF (degree of freedom) inertial measurement unit (IMU), a pressure sensor that is connected to the Gumstix via a 12-bit analog-to-digital converter (ADC) and LEDs for user feedback. The ADC and IMU both communicate over I2C. The LEDs communicate to the Gumstix through general purpose input/output (GPIO). Figure 1 shows a high-level explanation of hardware interfaces and Figure 2 provides an illustration of the system overview. All software was written in C and runs exclusively on the Gumstix Verdex Pro. A Linux kernel module was written to interact with the LEDs from the user-space program that performs data capture and analysis. IMU data was smoothed and corrected in real-time with an open-source attitude and heading reference system (AHRS) provided by Mahony [3][4]. A circular buffer queue was used to store and retrieve sensor data for recording and analysis. Punch classification compares accelerometer values at each data point and chooses the gesture with smallest discrepancy.

Figure 1
This high-level diagram details the data transfer connections made between the main hardware and software components of the Hit-Rec.

Figure 2
Overview of the software architecture for translating IMU and Pressure data to user feedback

Each of three LEDs on the Hit-Rec glove represents a different gesture type. After the “punchomatic” program is started, the user is prompted to record three gestures by way of three flashing LEDs. In the background, IMU data is continuously being recorded. The first, yellow LED flashes until an impact is registered, at which point the last 50 frames of IMU data are used as the “fingerprint“ for the gesture. This gesture fingerprint is stored for the rest of the session. Two additional gestures are recorded in an identical manner using the red and blue LEDs for the subsequent punches. After three gestures have been recorded, the user can punch in any form and the Hit-Rec will classify the new punch according to the three recently recorded punch gestures. Feedback on the most closely related punch is presented by lighting up the corresponding LED of the originally recorded gesture when a new punch occurs.

SENSORS

We used the Adafruit LSM9DS0 with breakout board as an IMU sensor and a force-sensitive resistor (FSR) from Adafruit as a pressure sensor. Both sensors communicate over I2C, which the pressure sensor achieves through an ADC. …

Read the full article in the June 335 issue of Circuit Cellar

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Wide Range Power Monitor Embeds ADCs

Analog Devices, acquired earlier this year by Linear Technology, has announced the LTC2992, a wide range I²C system monitor that monitors the current, voltage and power of two 0 V to 100 V rails without additional circuitry. The LTC2992 has flexible power supply options, deriving power from a 3 V to 100 V  monitored supply, a 2.7 V to 100 V secondary supply, or from the on-board shunt regulator. These supply options eliminate the need for a separate buck regulator, shunt regulator or inefficient resistive divider while monitoring any 0 V to 100 V rail. The LTC2992 is a simple, single-IC solution that uses three delta-sigma ADCs and a multiplier to provide 8- or 12-bit current and voltage measurements and 24-bit power readings.

LTC2992The LTC2992’s wide operating range is ideal for many applications, especially 48V telecom equipment, advanced mezzanine cards (AMC) and blade servers. The onboard shunt regulator provides support for supplies greater than 100V and negative supply monitoring. The LTC2992 measures current and voltage either continuously or on-demand, calculates power and stores all of this information along with minimum and maximum values in I²C accessible registers. Four GPIOs can also be configured as ADC inputs to measure neighboring auxiliary voltages. Measurements are made with only ±0.3% of total unadjusted error (TUE) over the entire temperature range. If any parameter trips the user-programmable thresholds, the LTC2992 flags an alert register and pin per the SMBus alert response protocol. The 400 kHz I²C interface features nine device addresses, a stuck bus reset timer, and a split SDA pin that simplifies I²C opto-isolation.  The LTC2992-1 version offers an inverted data output I²C pin for use with inverting opto-isolator configurations.

The LTC2992 and LTC2992-1 are offered in commercial, industrial and automotive versions, supporting operating temperature ranges from 0°C to 70°C, –40°C to 85°C and –40°C to 125°C, respectively. Both versions are available today in RoHS-compliant, 16-lead 4mm x 3mm DFN and 16-lead MSOP packages. Pricing starts at $3.85 each in 1,000-piece quantities. Please visit www.linear.com/products/power_monitors for more product selection and information.

Summary of Features:

  • Rail-to-Rail Input Range: 0 V to 100 V
  • Wide Input Supply Range: 2.7 V to 100 V
  • Shunt Regulator for Supplies >100 V
  • Three Delta-Sigma ADCs with Less Than ±0.3% TUE
  • 12-Bit Resolution for Currents & Voltages
  • Four GPIOs Configurable as ADC Inputs
  • Shutdown Mode with IQ < 50 µA
  • I²C Interface
  • Split SDA Pin Eases Opto-Isolation
  • Available in 16-Lead 4mm x 3mm DFN & 16-Lead MSOP Packages

Analog Devices | www.analog.com

Linear Technology | www.linear.com

Sensor Node Gets LoRaWAN Certification

Advantech offers its standardized M2.COM IoT LoRaWAN certified sensor node WISE-1510 with integrated ARM Cortex-M4 processor and LoRa transceiver. The module the  is able to provide multi-interfaces for sensors and I/O control such as UART, I2C, SPI, GPIO, PWM and ADC. The WISE-1510 sensor node is well suited for for smart cities, WISE-1510_3D _S20170602171747agriculture, metering, street lighting and environment monitoring. With power consumption optimization and wide area reception, LoRa  sensors or applications with low data rate requirements can achieve years of battery life and kilometers of long distance connection.

WISE-1510 has has received LoRaWAN certification from the LoRa Alliance. Depending on deployment requirements, developers can select to use Public LoRaWAN network services or build a private LoRa system with WISE-3610 LoRa IoT gateway. Advantech’s WISE-3610  is a Qualcomm ARM Cortex A7 based hardware platform with private LoRa ecosystem solution that can connect up to 500 WISE-1510 sensor node devices. Powered by Advantech’s WISE-PaaS IoT Software Platform, WISE-3610 features automatic cloud connection through its WISE-PaaS/WISE Agent service, manages wireless nodes and data via WSN management APIs, and helps customers streamline their IoT data acquisition development through sensor service APIs, and WSN drivers.

Developers can leverage microprocessors on WISE-1510 to build their own applications. WISE-1510 offers unified software—ARM Mbed OS and SDK for easy development with APIs and related documents. Developers can also find extensive resources from Github such as code review, library integration and free core tools. WISE-1510 also offers worldwide certification which allow developers to leverage their IoT devices anywhere. Using Advantech’s WISE-3610 LoRa IoT Gateway, WISE-1510 can be connected to WISE-  PaaS/RMM or  ARM Mbed Cloud service with IoT communication protocols including LWM2M, CoAP, and MQTT. End-to-end integration assists system integrators to overcome complex challenges and helps them build IoT applications quickly and easily.

WISE-1510 features and specifications:

  • ARM Cortex-M4 core processor
  • Compatible support for public LoRaWAN or private LoRa networks
  • Great for low power/wide range applications
  • Multiple I/O interfaces for sensor and control
  • Supports wide temperatures  -40 °C to 85 °C

Advantech | www.advantech.com

Analog ICs Meet Industrial System Needs

Jeff Lead Image Analog Inustrial

Connectivity, Control and IIoT

Whether it’s connecting with analog sensors or driving actuators, analog ICs play many critical roles in industrial applications. Networked systems add new wrinkles to the industrial analog landscape.

By Jeff Child

While analog ICs are important in a variety of application areas, their place in the industrial market stands out. Industrial applications depend heavily on all kinds of interfacing between real-world analog signals and the digital realm of processing and control. Today’s factory environments are filled with motors to control, sensors to link with and measurements to automate. And as net-connected systems become the norm, analog chip vendors are making advances to serve the new requirements of the Industrial Internet-of-Things (IIoT) and Smart Factories.

It’s noteworthy, for example, that Analog Devices‘ third quarter fiscal year 2017 report this summer cited the “highly diverse and profitable industrial market” as the lead engine of its broad-based year-over-year growth. Taken together, these factors all make industrial applications a significant market for analog IC vendors, and those vendors are keeping pace by rolling out diverse solutions to meet those needs.

Figure 1

Figure 1 This diagram from Texas Instruments illustrates the diverse kinds of analog sub-systems that are common in industrial systems—an industrial drive/control system in this case.

While it’s impossible to generalize about industrial systems, Figure 1 illustrates the diverse kinds of analog sub-systems that are common in industrial systems—industrial drive/control in that case. All throughout 2017, manufacturers of analog ICs have released a rich variety of chips and development solutions to meet a wide range of industrial application needs.

SOLUTIONS FOR PLCs

Programmable Logic Controllers (PLCs) remain a staple in many industrial systems. As communications demands increase and power management gets more difficult, transceiver technologies have evolved to keep up. PLC and IO-Link gateway systems must dissipate large amounts of power depending. That amount of power is often tied to I/O configuration—IO-Link, digital I/O and/or analog I/O. As these PLCs evolve into new Industrial 4.0 smart factories, special attention must be considered to achieve smarter, faster, and lower power solutions. Exemplifying those trends, this summer Maxim Integrated announced the MAX14819, a dual-channel, IO-Link master transceiver.

The architecture of the MAX14819 dissipates 50% less heat compared to other IO-Link Master solutions and is fully compatible in all modes for IO-Link and SIO compliance. It provides robust L+ supply controllers with settable current limiting and reverse voltage/current protection to help ensure robust communications with the lowest power consumption. With just one microcontroller, the integrated framer/UART enables a scalable and cost-effective architecture while enabling very fast cycle times (up to
400 µs) and reducing latency. The MAX14819 is available in a 48-pin (7 mm x 7 mm) TQFN package and operates over a -40°C to +125°C temperature range.  …

Read the full article in the November 328 issue of Circuit Cellar

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Microcontrollers Target Smart Water Meters

Texas Instruments has unveiled a new family of MSP430 microcontrollers with an integrated ultrasonic sensing analog front end that enables smart water meters to deliver higher accuracy and lower power consumption. In addition, TI introduced two new reference designs that make it easier to design modules for adding automated meter reading (AMR) capabilities to existing mechanical water meters. The new MCUs and reference designs support the growing demand for more accurate water meters and remote meter reading to enable efficient water resource management, accurate measurement and timely billing.

New ultrasonic MCUs and new reference designs make both electronic and mechanical water meters smarter (PRNewsfoto/Texas Instruments Incorporated)

New ultrasonic MCUs and new reference designs make both electronic and mechanical water meters smarter.

As part of the ultra-low-power MSP430 MCU portfolio for sensing and measurement, the new MSP430FR6047 MCU family lets developers add more intelligence to flow meters by taking advantage of a complete waveform capture feature and analog-to-digital converter (ADC)-based signal processing. This technique enables more accurate measurement than competitive devices, with precision of 25 ps or better, even at flow rates less than 1 liter per hour. In addition, the integrated MSP430FR6047 devices reduce water meter system component count by 50 percent and power consumption by 25 percent, enabling a meter to operate without having to charge the battery for 10 or more years. The new MCUs also integrate a low-energy accelerator module for advanced signal processing, 256 KB of ferroelectric random access memory (FRAM), a LCD driver and a metering test interface.

The MSP430 Ultrasonic Sensing Design Center offers a comprehensive development ecosystem that allows developers to get to market in months. The design center provides tools for quick development and flexibility for customization, including software libraries, a GUI, evaluation modules with metrology and DSP libraries.

TI’s new Low-Power Water Flow Measurement with Inductive Sensing Reference Design is a compact solution for the electronic measurement of mechanical flow meters with low power consumption for longer battery life. Enabled by the single-chip SimpleLink dual-band CC1350 wireless MCU, this reference design also gives designers the ability to add dual-band wireless communications for AMR networks. Designers can take advantage of the reference design’s small footprint to easily retrofit existing mechanical flow meters, enabling water utilities to add AMR capability while avoiding expensive replacement of deployed meters. The CC1350 wireless MCU consumes only 4 µA while measuring water flow rates, enabling longer product life.

A second new reference design is an ultra-low power solution based on the SimpleLink Sub-1 GHz CC1310 wireless MCU. The Low-Power Wireless M-Bus Communications Module Reference Design uses TI’s wireless M-Bus software stack and supports all wireless M-Bus operating modes in the 868-MHz band. This reference design provides best-in-class power consumption and flexibility to support wireless M-Bus deployments across multiple regions.

Texas Instruments | www.ti.com

USB Data Acq System Features Simple Expansion

DATAQ Instruments has announced the release of its model DI-2108-P USB data acquisition (DAQ) system with 16-bit ADC resolution, programmable gain and ChannelStretch technology. The model DI-2108-P provides eight analog input channels each with 2.5-, 5- and 10-volt unipolar and bi-polar programmable measurement ranges. DATAQ Instruments di2108-product-photo-press-releaseThe DI-2108-P also provides 7 digital ports, each configurable as an input or a switch. Two ports can be programmed as counter and frequency measurement inputs. The instrument’s maximum sampling throughput rate is 160 kHz.

The ChannelStretch feature of the DI-2108-P makes channel expansion as easy as adding another device. Plug a second device into a computer and double the channel count of both analog and digital channels. Using USB hubs, plug up to sixteen devices into a single PC for a maximum count of 128 analog and 112 digital channels. And all of them are acquired synchronously at a maximum sample throughput rate of at least 480 kHz. DI-2108-P software support includes ready-to run WinDaq data acquisition software, .Net class, ActiveX controls and a fully documented communication protocol to deploy the instrument on any platform. The unit is priced at $349.

DATAQ Instruments | www.dataq.com

Getting Started with PSoC MCUs (Part 3)

Data Conversion, Capacitive Sensing and More

In the previous parts of this series, Nishant laid the groundwork for getting up and running with the PSoC. Here he tackles the chip’s more complex features like Data Conversion and CapSense.

By Nishant Mittal
Systems Engineer, Cypress Semiconductor

In the previous two parts of this “Getting started with PSoC” series, I have hopefully provided you with a good base of knowledge about PSoC devices. Here, in this final part it’s time to get more in depth and discuss various data conversion protocols in PSoC and provide some design examples. I’ll also cover interfacing various peripherals with the Photo 1microcontroller. We’ll also get into how to transition from a bare silicon PSoC chip or PSoC development board to using the chip in your project.

Data conversion with PSoC

Data Conversion is an important block in any kind of instrumentation system or Internet of Things implementation. In fact, any application that uses sensors or interfaces to the external environment is an application in which Data Conversion is an integral part of the system. Although digital sensors are available today, the lower costs of analog sensors shouldn’t be overlooked.

 

PSoC Creator has a Data Conversion component that enables designers to code efficiently with less effort. The photo above shows the screenshot of the ADC (analog-to-digital conversion) component in PSoC Creator. The photo above also shows the configuration setting for ADC. First off, we need to set the Channel sampling rate (SPS). Second, we need to set the voltage reference which is necessary to do the comparison of analog signals. Here we use VDDA/2 or VDDA which is 5 V. You can select whether you For web Figure 1want a single-ended ADC or differential ADC by simply clicking the appropriate tab from the component configuration. Clock source needs to be chosen. If the source is chosen to be internal, the PLL from the internals of chip are used—otherwise you’d have to connect an external crystal to the controller using the development kit CY8CKIT-044. Other advanced settings are available for complex programs—but most of those aren’t needed in most intermediate applications.

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16-Bit, 1.5-Msps Per Channel Octal Simultaneous Sampling SAR ADC

Linear Technology Corp. recently introduced the LTC2320-16 16-bit, 1.5-Msps per channel, no-latency successive approximation register (SAR) ADC. Featuring eight simultaneously sampling channels supporting a rail-to-rail input common mode range, the LTC2320-16 offers a flexible analog front end that accepts fully differential, unipolar or bipolar analog input signals. It also accepts arbitrary input signals and maintains an 82-dB signal-to-noise ratio (SNR) and high common mode rejection ratio (CMRR) of 102 dB when sampling input signals up to the Nyquist frequency. Linear LTC2320-16

 

The LTC2320-16’s specs, features, and benefits:

  • Wide input bandwidth enables the digitization of input signals up to the Nyquist frequency of 750 kHz
  • 1.5 Msps per channel throughput rate
  • Eight simultaneous sampling channels
  • ±2 LSB INL (typ)
  • Guaranteed 16-bit, no missing codes
  • 8.192 VPP true differential inputs with rail-to-rail common mode
  • 82-dB SNR (typ) at fIN = 500 kHz
  • –90-dB THD (Typ) at fIN = 500kHz
  • Guaranteed operation to 125°C
  • Single 3.3- or 5-V supply
  • Low drift (20 ppm/°C max) 2.048- or 4.096-V internal reference
  • 1.8-to-2.5-V I/O voltages
  • CMOS or LVDS SPI-Compatible Serial I/O
  • Power dissipation 20 mW/Ch (typ, 5-V operation)
  • 52-pin 7 mm × 8 mm QFN package

The LTC2320-16 is available in commercial, industrial, and automotive (–40° to 125°C) temperature grades. Pricing begins at $16.50 each in 1,000-piece quantities. The DC2395A evaluation board for the LTC2320 SAR ADC family is available at www.linear.com/demo.

Source: Linear Technology

Fast 16-bit ADC, Four-Channel 14-bit ADC, & Digital Variable Gain Amp

Texas Instruments launched the ADS54J60, which is the industry’s first 16-bit 1-GSPS ADC and the first to achieve over 70 dBFS signal-to-noise ratio (SNR) at 1-GSPS. Texas instruments also announced the highest-density, four-channel, 14-bit 500-MSPS ADC, the ADS54J54. To optimize the signal chain, TI’s new 4.5-GHz LMH6401 fully differential digital variable gain amplifier (DVGA) offers the widest bandwidth with DC coupling and allows signal acquisition of low and high frequencies without the limitation of baluns used in AC-coupled systems. These ADCs work together with the amplifier to provide the highest performance, lowest power and space savings in defense and aerospace, test and measurement, and communication infrastructure applications.Texas Instruments

All ICs are now sampling. The ADS54J54 costs $500 in 1,000-unit quantities. The ADS54J60 will be available in Q4 2015 for $705 in 1,000-unit quantities. The LMH6401 costs $10.95 in 1,000-unit quantities.

Source: Texas Instruments

New AFEs for Single-Phase Smart Meters & Power Monitoring

Microchip Technology has announced the completion of its MCP391X energy-measurement Analog Front End (AFE) family.  The MCP3919 and MCP3912 integrate three and four channels of 24-bit, delta-sigma ADC, respectively. They have an accuracy of 93.5 dB SINAD, –107-dB THD, and 112-dB SFDR for precise signal acquisition and higher-perforce end products.microchipMCP391Xafe

Microchip also announced two new tools to aid in the development of energy systems using the new AFEs.  The MCP3912 Evaluation Board (part # ADM00499) and MCP3919 Evaluation Board (part # ADM00573) are each available for $129.99.

The MCP3912 and MCP3919 AFEs are both available today for sampling and volume production, with prices starting at $1.84 each in 5,000-unit quantities.  Both AFEs are offered in 28-pin QFN and SSOP packages.

Source: Microchip Technology

Measuring Jitter (EE Tip #132)

Jitter is one of the parameters you should consider when designing a project, especially when it involves planning a high-speed digital system. Moreover, jitter investigation—performed either manually or with the help of proper measurement tools—can provide you with a thorough analysis of your product.

There are at least two ways to measure jitter: cycle-to-cycle and time interval error (TIE).

WHAT IS JITTER?
The following is the generic definition offered by The International Telecommunication Union (ITU) in its G.810 recommendation. “Jitter (timing): The short-term variations of the significant instants of a timing signal from their ideal positions in time (where short-term implies that these variations are of frequency greater than or equal to 10 Hz).”

First, jitter refers to timing signals (e.g., a clock or a digital control signal that must be time-correlated to a given clock). Then you only consider “significant instants” of these signals (i.e., signal-useful transitions from one logical state to the other). These events are supposed to happen at a specific time. Jitter is the difference between this expected time and the actual time when the event occurs (see Figure 1).

Figure 1—Jitter includes all phenomena that result in an unwanted shift in timing of some digital signal transitions in comparison to a supposedly “perfect” signal.

Figure 1—Jitter includes all phenomena that result in an unwanted shift in timing of some digital signal transitions in comparison to a supposedly “perfect” signal.

Last, jitter concerns only short-term variations, meaning fast variations as compared to the signal frequency (in contrast, very slow variations, lower than 10 Hz, are called “wander”).

Clock jitter, for example, is a big concern for A/D conversions. Read my article on fast ADCs (“Playing with High-Speed ADCs,” Circuit Cellar 259, 2012) and you will discover that jitter could quickly jeopardize your expensive, high-end ADC’s signal-to-noise ratio.

CYCLE-TO-CYCLE JITTER
Assume you have a digital signal with transitions that should stay within preset time limits (which are usually calculated based on the receiver’s signal period and timing diagrams, such as setup duration and so forth). You are wondering if it is suffering from any excessive jitter. How do you measure the jitter? First, think about what you actually want to measure: Do you have a single signal (e.g., a clock) that could have jitter in its timing transitions as compared to absolute time? Or, do you have a digital signal that must be time-correlated to an accessible clock that is supposed to be perfect? The measurement methods will be different. For simplicity, I will assume the first scenario: You have a clock signal with rising edges that are supposed to be perfectly stable, and you want to double check it.

My first suggestion is to connect this clock to your best oscilloscope’s input, trigger the oscilloscope on the clock’s rising edge, adjust the time base to get a full period on the screen, and measure the clock edge’s time dispersion of the transition just following the trigger. This method will provide a measurement of the so-called cycle-to-cycle jitter (see Figure 2).

Figure 2—Cycle-to-cycle is the easiest way to measure jitter. You can simply trigger your oscilloscope on a signal transition and measure the dispersion of the following transition’s time.

Figure 2—Cycle-to-cycle is the easiest way to measure jitter. You can simply trigger your oscilloscope on a signal transition and measure the dispersion of the following transition’s time.

If you have a dual time base or a digital oscilloscope with zoom features, you could enlarge the time zone around the clock edge you are interested in for more accurate measurements. I used an old Philips PM5786B pulse generator from my lab to perform the test. I configured the pulse generator to generate a 6.6-MHz square signal and connected it to my Teledyne LeCroy WaveRunner 610Zi oscilloscope. I admit this is high-end equipment (1-GHz bandwidth, 20-GSPS sampling rate and an impressive 32-M word memory when using only two of its four channels), but it enabled me to demonstrate some other interesting things about jitter. I could have used an analog oscilloscope to perform the same measurement, as long as the oscilloscope provided enough bandwidth and a dual time base (e.g., an old Tektronix 7904 oscilloscope or something similar). Nevertheless, the result is shown in Figure 3.

Figure 3—This is the result of a cycle-to-cycle jitter measurement of the PM5786A pulse generator. The bottom curve is a zoom of the rising front just following the trigger. The cycle-to-cycle jitter is the horizontal span of this transition over time, here measured at about 620 ps.

Figure 3—This is the result of a cycle-to-cycle jitter measurement of the PM5786A pulse generator. The bottom curve is a zoom of the rising front just following the trigger. The cycle-to-cycle jitter is the horizontal span of this transition over time, here measured at about 620 ps.

This signal generator’s cycle-to-cycle jitter is clearly visible. I measured it around 620 ps. That’s not much, but it can’t be ignored as compared to the signal’s period, which is 151 ns (i.e., 1/6.6 MHz). In fact, 620 ps is ±0.2% of the clock period. Caution: When you are performing this type of measurement, double check the oscilloscope’s intrinsic jitter as you are measuring the sum of the jitter of the clock and the jitter of the oscilloscope. Here, the latter is far smaller.

TIME INTERVAL ERROR
Cycle-to-cycle is not the only way to measure jitter. In fact, this method is not the one stated by the definition of jitter I presented earlier. Cycle-to-cycle jitter is a measurement of the timing variation from one signal cycle to the next one, not between the signal and its “ideal” version. The jitter measurement closest to that definition is called time interval error (TIE). As its name suggests, this is a measure of a signal’s transitions actual time, as compared to its expected time (see Figure 4).

Figure 4—Time interval error (TIE) is another way to measure jitter. Here, the actual transitions are compared to a reference clock, which is supposed to be “perfect,” providing the TIE. This reference can be either another physical signal or it can be generated using a PLL. The measured signal’s accumulated plot, triggered by the reference clock, also provides the so-called eye diagram.

Figure 4—Time interval error (TIE) is another way to measure jitter. Here, the actual transitions are compared to a reference clock, which is supposed to be “perfect,” providing the TIE. This reference can be either another physical signal or it can be generated using a PLL. The measured signal’s accumulated plot, triggered by the reference clock, also provides the so-called eye diagram.

It’s difficult to know these expected times. If you are lucky, you could have a reference clock elsewhere on your circuit, which would supposedly be “perfect.” In that case, you could use this reference as a trigger source, connect the signal to be measured on the oscilloscope’s input channel, and measure its variation from trigger event to trigger event. This would give you a TIE measurement.

But how do you proceed if you don’t have anything other than your signal to be measured? With my previous example, I wanted to measure the jitter of a lab signal generator’s output, which isn’t correlated to any accessible reference clock. In that case, you could still measure a TIE, but first you would have to generate a “perfect” clock. How can this be accomplished? Generating an “ideal” clock, synchronized with a signal, is a perfect job for a phase-locked loop (PLL). The technique is explained my article, “Are You Locked? A PLL Primer” (Circuit Cellar 209, 2007.) You could design a PLL to lock on your signal frequency and it could be as stable as you want (provided you are willing to pay the expense).

Moreover, this PLL’s bandwidth (which is the bandwidth of its feedback filter) would give you an easy way to zoom in on your jitter of interest. For example, if the PLL bandwidth is 100 Hz, the PLL loop will capture any phase variation slower than 100 Hz. Therefore, you can measure the jitter components faster than this limit. This PLL (often called a carrier recovery circuit) can be either an actual hardware circuit or a software-based implementation.

So, there are at least two ways to measure jitter: Cycle-to-cycle and TIE. (As you may have anticipated, many other measurements exist, but I will limit myself to these two for simplicity.) Are these measurement methods related? Yes, of course, but the relationship is not immediate. If the TIE is not null but remains constant, the cycle-to-cycle jitter is null.  Similarly, if the cycle-to-cycle jitter is constant but not null, the TIE will increase over time. In fact, the TIE is closely linked to the mathematical integral over time of the cycle-to-cycle jitter, but this is a little more complex, as the jitter’s frequency range must be limited.

Editor’s Note: This is an excerpt from an article written by Robert Lacoste, “Analyzing a Case of the Jitters: Tips for Preventing Digital Design Issues,” Circuit Cellar 273, 2013.

Real-Time Processing for PCIe Digitizers

Agilent U5303A PCIe 12bit High-Speed DigitizerThe U5303A digitizer and the U5340A FPGA development kit are recent enhancements to Agilent Technologies’s PCI Express (PCIe) high-speed digitizers. The U5303A and the U5340A FPGA add next-generation real-time peak detection functionalities to the PCIe devices.

The U5303A is a 12-bit PCIe digitizer with programmable on-board processing. It offers high performance in a small footprint, making it an ideal platform for many commercial, industrial, and aerospace and defense embedded systems. A data processing unit (DPU) based on the Xilinx Virtex-6 FPGA is at the heart of the U5303A. The DPU controls the module functionality, data flow, and real-time signal processing. This feature enables data reduction and storage to be carried out at the digitizer level, minimizing transfer volumes and accelerating analysis.

The U5340A FPGA development kit is designed to help companies and researchers protect their IP signal-processing algorithms. The FPGA kit enables integration of an advanced real-time signal processing algorithm within Agilent Technologies’s high-speed digitizers. The U5340A features high-speed medical imaging, analytical time-of-flight, lidar ranging, non-destructive testing, and a direct interface to digitizer hardware elements (e.g., the ADC, clock manager, and memory blocks). The FPGA kit includes a library of building blocks, from basic gates to dual-port RAM; a set of IP cores; and ready-to-use scripts that handle all aspects of the build flow.

Contact Agilent Technologies for pricing.

Agilent Technologies, Inc.
www.agilent.com