Linear and RF

Application Notes

AN-1182: Understanding and Optimizing the AFC Loop on the ADF7021 for Minimum Preamble

Remote transceivers within radio communication networks use their own independent clock sources, and are thus susceptible to frequency errors. When a transmitter initiates a communication link, the associated receiver must correct these errors during the preamble phase of the data packet to ensure correct demodulation. An effective design block that performs this correction is an automatic frequency control (AFC) loop. This 7‑page Application Note provides information on how AFC is implemented and optimized on the ADF7021, ADF7021-N, and ADF7021-V.

AN-1165: Op Amps for MEMS Microphone Preamp Circuits

A microphone preamp circuit amplifies a microphone’s output signal to match the input level of the following device. Matching the peaks of the microphone’s signal level to the full-scale input voltage of an ADC makes maximum use of the ADC’s dynamic range and reduces the noise that subsequent processing may add to the signal. The MEMS microphone has a single-ended output, so a single op amp stage can be used as a preamp to add gain to the microphone signal or to buffer the output. This Application Note covers some of the key op amp specifications to consider for a preamp design, shows a few basic circuits, and provides a table of Analog Devices op amps that are appropriate for a preamp design. The ADMP504 MEMS analog microphone with 65 dB SNR is used as an example to describe different design choices.

Circuits from the Lab

CN0325: PLC/DCS Universal Analog Input Using Either 4 or 6 Pin Terminal Block

This circuit provides two, 16-bit, fully isolated, universal analog input channels suitable for programmable logic controller (PLC) and distributed control system (DCS) modules. Both channels are software programmable and support a number of voltage and current ranges and thermocouple and RTD types. The inputs are protected for dc overvoltage conditions of ±30 V. The demonstration board contains two fully isolated universal input channels: in one, the voltage, current, thermocouple, and RTD inputs all share the same terminals to minimize the number of pins required; in the other, separate terminals for voltage/current inputs and thermocouple/RTD inputs provides a lower part count and component cost.

CN0312: Dual-Channel Colorimeter with Programmable Gain Transimpedance Amplifiers and Synchronous Detectors

This dual-channel colorimeter, which features a modulated light source transmitter and a synchronous detector receiver, measures the ratio of light absorbed by the sample and reference containers at three different wavelengths, providing an efficient solution for many chemical analysis and environmental monitoring instruments that measure concentrations and characterize materials through absorption spectroscopy.

Broadband, Low Error Vector Magnitude (EVM) Direct Conversion Transmitter Using LO Divide-by-2 Modulator (CN0311)

This broadband direct-conversion transmitter (analog baseband in, RF out) supports RF frequencies from 30 MHz to 2.2 GHz using a phase-locked loop (PLL) with an on-chip broadband voltage-controlled oscillator (VCO). Unlike modulators that use a divide-by-1 local oscillator (LO) stage, harmonic filtering of the LO is not required as long as the LO inputs to the modulator are driven differentially. The ADF4351 provides differential RF outputs and is, therefore, an excellent match. This PLL-to-modulator interface is useful for all I/Q modulators and I/Q demodulators that contain a 2XLO-based phase splitter.

CN0295: Flexible, 4 mA-to-20 mA Pressure Sensor Transmitter with Voltage or Current Drive

This flexible current transmitter converts the differential voltage output from a pressure sensor to a 4-mA to 20-mA current. Optimized for a wide variety of bridge-based voltage or current driven pressure sensors, it utilizes only five active devices and has a total unadjusted error of less than 1%. The power supply voltage can range from 7 V to 36 V depending on the component and sensor driver configuration. The input of the circuit is protected for ESD and voltages beyond the supply rail, making it ideal for industrial applications.

CN0288: LVDT Signal Conditioning Circuit

This complete, adjustment-free, linear variable differential transformer (LVDT) signal conditioning circuit can accurately measure linear displacement (position). It uses the AD598 LVDT signal conditioner, which integrates a sine wave oscillator and a power amplifier to generate the excitation signals that drive the primary side of the LVDT. The system has 82-dB dynamic range and 250-Hz bandwidth, making it ideal for precision industrial position and gauging applications. This Circuit Note discusses basic LVDT theory and the design steps used to optimize the circuit for a chosen bandwidth.

Broadband Low Error Vector Magnitude (EVM) Direct Conversion Transmitter (CN0285)

This circuit is a complete implementation of the analog portion of a broadband direct conversion transmitter (analog baseband in, RF out). It supports RF frequencies from 500 MHz to 4.4 GHz using a phase-locked loop (PLL) with a broadband, integrated voltage-controlled oscillator (VCO). Harmonic filtering of the local oscillator (LO) from the PLL ensures excellent quadrature accuracy, sideband suppression, and low EVM. Low noise, low dropout regulators (LDOs) ensure that the power management scheme has no adverse impact on phase noise and EVM. This combination of components represents industry leading direct conversion transmitter performance over a frequency range of 500 MHz to 4.4 GHz.

Providing Fixed Power Gain at the Output of an IQ Modulator (CN0283)

Whether an IQ modulator is used in a direct conversion application or as an upconverter to a first intermediate frequency (IF), some gain is generally applied directly after the IQ modulator. This circuit note describes how to choose an appropriate driver amplifier to provide the first stage of gain at the output of an IQ modulator. This circuit uses the ADL5375 IQ modulator and the ADL5320 driver amplifier, which are well matched from a system performance level. Because these devices are well matched in terms of their dynamic ranges, a simple direct connection between the IQ modulator and the RF driver amplifier is recommended without any need for attenuation between the devices.

High IF Sampling Receiver Front End with Band-Pass Filter (CN0279)

This band-pass receiver front-end is based on the ADL5565 ultralow-noise differential amplifier driver and the AD9642 14-bit, 250-MSPS analog-to-digital converter (ADC). The third-order Butterworth antialiasing filter is optimized based on the performance and interface requirements of the amplifier and ADC. The total insertion loss due to the filter network and other components is only 5.8 dB. The overall circuit has a bandwidth of 18 MHz with a pass-band flatness of 3 dB. With a 127-MHz analog input, it features 71.7-dBFS signal-to-noise ratio (SNR) and 92-dBc spurious-free dynamic range (SFDR). The sampling frequency is 205 MSPS, thereby positioning the IF input signal in the second Nyquist zone between 102.5 MHz and 205 MHz.

Complete Broadband Video-over-UTP Driver and Receiver Solution for RGB, YPbPr, and More (CN0275)

Originally intended to carry LAN traffic, Cat-5e UTP cable is widely used in many other signal transmission applications because of its respectable performance and low cost. Signals transported over UTP cable suffer from three major impairments that degrade video quality: nonlinear bandlimiting, low-frequency loss, and delay skew. This circuit overcomes these impairments by using the AD8122 triple receiver/equalizer to restore the high frequency content of the video signals while also providing flat gain. The AD8120 triple skew-compensating analog delay line adds delay to the two earliest arriving signals such that the three received signals are properly aligned in time. The AD8147 triple driver provides the required single-ended-to-differential conversion of the source video signals.

K-Type Thermocouple Measurement System with Integrated Cold Junction Compensation (CN0271)

This circuit is a complete thermocouple signal-conditioning circuit with cold-junction compensation followed by a 16-bit sigma-delta (Σ-Δ) analog-to-digital converter (ADC). The AD8495 thermocouple amplifier provides a simple, low-cost solution for measuring K-type thermocouple temperatures, including cold-junction compensation. Its fixed-gain instrumentation amplifier scales the small thermocouple voltage to provide a 5 mV/°C output. The amplifier’s high common-mode rejection blocks common-mode noise picked up by the long thermocouple leads. For additional protection, its high-impedance inputs make it easy to add extra filtering. The AD8476 differential amplifier provides the correct signal levels and common-mode voltage to drive the AD7790 16-bit, Σ-Δ ADC, providing a compact, low-cost solution for thermocouple signal conditioning and high-resolution analog-to-digital conversion.

New Product Briefs

June 2013

18-MHz, low-power Variable-Gain Amplifier

The AD8338 variable-gain amplifier is ideal for applications that require a fully differential signal path, low power, low noise, and a well-defined gain over frequencies from LF to 18 MHz. Single-ended sources can be used if required. The basic gain function is linear-in-dB with a nominal 0 dB to 80 dB gain range set by a 0.1 V to 1.1 V control voltage. The gain range can be adjusted up or down with an external resistor. Additional circuits enable offset correction and automatic gain control. Access to the internal summing nodes enables users to customize gain, bandwidth, input impedance, and noise profile. Operating on a single 3.0-V to 5.0-V supply, the AD8338 draws 3 mA. Available in a 16-lead LFCSP package, it is specified from –40°C to +85°C and priced at $4.81 in 1000s.

Precision Instrumentation Amplifier features low-power, rail-to-rail output

The AD8422 high-precision, low-power, low-noise instrumentation amplifier delivers ultralow distortion over the full output range, and the industry’s best performance per microampere. The third generation device achieves higher dynamic range and lower errors than its predecessors, while consuming less than one-third of the power. Very low bias current minimizes errors with high source impedance, allowing multiple sensors to be multiplexed to the inputs. Low voltage noise and low current noise make it an ideal choice for measuring a Wheatstone bridge. The wide input range and rail-to-rail output enable true single-supply applications. High ESD immunity, and inputs that are protected from voltages up to 40 V from the opposite supply rail, ensure reliability without sacrificing noise performance. A single resistor sets the gain from 1 to 1000. The reference pin can be used to apply a precise offset to the output voltage. Operating on a single 3.6-V to 36-V supply or ±1.8-V to ±18-V supplies, the AD8422 draws 300 µA. Available in 8-lead MSOP and SOIC packages, it is specified from –40°C to +85°C and priced from $2.10 in 1000s.

Precision Difference Amplifier has very high common-mode voltage range

The AD8479 difference amplifier offers a very high input common-mode voltage range. The precision device allows accurate measurement of differential signals in the presence of common-mode voltages up to ±600 V. It can replace costly isolation amplifiers in applications that do not require galvanic isolation. Its low offset, low offset drift, low gain error drift, low common-mode rejection drift, and excellent CMRR over a wide frequency range make it an ideal sensing current, monitoring batteries, and controlling motors. Operating on ±2.5-V to ±18-V supplies, the AD8479 draws 550 µA. Available in an 8-lead SOIC package, it is specified from –40°C to +125°C and priced from $2.81 in 1000s.

IF Receiver has 80-MHz bandwidth

The AD6677 intermediate frequency (IF) receiver supports multi-antenna systems in telecommunication applications that require high dynamic range, low power, and small size. It includes an 11-bit, 250-MSPS analog-to-digital converter (ADC), a noise shaping requantizer (NSR), a voltage reference, and a duty cycle stabilizer. The fully differential pipelined ADC with integrated error correction logic features a wide bandwidth switched capacitor sampling input. The ADC output is connected to the NSR, which can improve SNR from 65.9 dBFS for the entire Nyquist bandwidth to 76.3 dBFS for a 55 MHz bandwidth or 73.5 dBFS for an 82 MHz bandwidth. The output data is routed to an external JESD204B serial output lane that operates at current mode logic (CML) voltage levels. The receiver digitizes a wide spectrum of IF frequencies, reducing component cost and complexity compared with traditional analog techniques or less integrated digital methods. Operating on a single 1.7-V to 1.9-V supply, the AD6677 dissipates 500 mW with NSR enabled, 266 mW in standby mode, and 9 mW in power-down mode. Available in a 32-lead LFCSP package, it is specified from –40°C to +85°C and priced at $44.20 in 1000s.

30-MHz to 6-GHz RF/IF Gain Blocks

The ADL5544/ADL5545 single-ended RF/IF gain block amplifiers offer broadband operation from 30 MHz to 6 GHz. Providing 17-/24-dB gain that is stable over frequency, temperature, and power supply, they achieve over 34-/36-dBm OIP3 using only 55/56 mA from a 5-V supply. Internally matched to 50 Ω at the input and output, they require only ac coupling capacitors, power supply decoupling capacitors, and a dc bias inductor. Fabricated on an InGaP HBT process, they feature an ESD rating of ±1.5 kV (Class 1C). Operating on a single 4.75-V to 5.25-V supply, the ADL5544/45 dissipate 275/280 mW. Available in a 3-lead SOT-89 package, they are specified from –40°C to +105°C and priced at $1.35 in 1000s.

May 2013

10-MHz to 10-GHz RMS Power Detector has 67-dB dynamic range

The ADL5906 TruPwr™ rms-responding power detector provides a 67-dB dynamic range over the 10-MHz to 10-GHz frequency range. Driven from a single-ended 50-Ω source, it does not require a balun or other external input tuning, making it versatile and easy to use to control transmitter power or indicate signal strength. It provides excellent temperature stability, significantly easing calibration routines. Accepting inputs with rms values from –65 dBm to +8 dBm with varying crest factors and bandwidths, it can handle GSM-EDGE, CDMA, W-CDMA, TD-SCDMA, WiMAX, and LTE signals. When used in measurement mode, the output is proportional to the log of the rms value of the input, with a scaling factor of 55 mV/dB. In controller mode, an applied voltage determines the power level. Operating on a single 4.75-V to 5.25-V supply, the ADL5906 consumes 68 mA at –60 dBm and 250 µA in power-down mode. A-/S-grades, specified from –40°C /–55°C to +105°C/+125°C, are available in 16‑lead LFCSP packages and priced at $5.59/$12.57 in 1000s.

April 2013

High-performance Isolated Error Amplifier offers alternative to optocouplers and shunt regulators

The ADuM3190 isolated error amplifier is ideal for linear feedback power supplies with primary side controllers. Its 400-kHz bandwidth, 0.5% typical initial accuracy at 25°C, and 1% total accuracy over temperature provides manufacturers of ac-to-dc and dc-to-dc power supplies, including those that are DOSA (Distributed-power Open Standards Alliance)-compliant, with a significant upgrade in speed and operating temperature range, as well as a 5× improvement in transient response. Designed with ADI’s iCoupler^® digital isolation technology, it eliminates the CTR (current-transfer ratio) of optocouplers that degrades over lifetime and limits operation to 85˚C. The ADuM3190 includes a high-accuracy 1.225-V reference and a wideband operational amplifier that can be used to set up a variety of commonly used power supply loop compensation techniques. Specified from –40°C to +125°C, it is available in a 16-lead QSOP package and priced at $1.04 in 1000s.

Technical Articles

Luis Orozco, Programmable-Gain Transimpedance Amplifiers Maximize Dynamic Range in Spectroscopy Systems, Analog Dialogue, 2013-05-01

David Buchanan, Input Magic, Analog Dialogue, 2013-05-01

Umesh Jayamohan, Understanding How Amplifier Noise Contributes to Total Noise in ADC Signal Chains, TechOnline India, 2013-04-30

David Guo, Choose Resistors to Minimize Errors in Grounded-Load Current Source, Analog Dialogue, 2013-04-01

James Bryant, Multipliers or Modulators, Analog Dialogue, 2013-04-01

John Ardizzoni, Noise Gain vs. Signal Gain, Analog Dialogue, 2013-03-06

Ryan Fletcher and Scott Wayne, Analog Devices' Engineering University--Why YOU Should Attend, Analog Dialogue, 2013-03-06

Ashraf Elghamrawi, High Performance Driver Amplifiers, Microwave Journal, 2013-02-14

Chau Tran, Marco Ablao, and Sherwin Gatchalian, Differential input to differential output amplifiers equal high temp solution, EE Times, 2013-02-06

Umesh Jayamohan, Understand How Amplifier Noise Contributes to Total Noise in ADC Signal Chains, Analog Dialogue, 2013-02-04

Chau Tran, Current transmitter operates at extremely high temperatures, EE Times, 2013-01-23

David Karpaty, Modeling Amplifiers as Analog Filters Increases SPICE Simulation Speed, Analog Dialogue, 2013-01-02

Mark Champion and Moshe Gerstenhaber, Complete, low-cost, software programmable ohmmeter measures micro-ohms, EDN, 2012-12-06

Alan Walsh, Front-End Amplifier and RC Filter Design for a Precision SAR Analog-to-Digital Converter, Analog Dialogue, 2012-12-03

Charly El-Khoury, Compensating Amplifiers That Are Stable at Gain ≥ 10 to Operate at Lower Gains, Analog Dialogue, 2012-12-03

Sandro Herrera and Moshe Gerstenhaber, Single-ended-to-differential converter has resistor-programmable gain, EDN, 2012-11-18

Reza Moghimi, Conditioning techniques for real-world sensors, EDN, 2012-11-15

Chau Tran and David Karpaty, Simple circuit measures RMS value of AC power line, EE Times, 2012-11-08

Reza Moghimi, Key benefits of input over-voltage protected op amps in systems, EDN, 2012-10-21

Rob Reeder, Dissecting The High-Speed Amplifier/AAF/ADC Interface, Electronic Design, 2012-10-16

Sandro Herrera and Moshe Gerstenhaber, Versatile, Low-Power, Precision Single-Ended-to-Differential Converter, Analog Dialogue, 2012-10-03

Eamon Nash, Problem Solving To Make RF And Mixed Signal Components Speak The Same Language, RF Globalnet, 2012-10-03

Mark Reisiger, Reduce Amplifier Noise Peaking To Improve SNR, Electronic Design, 2012-10-02

Reza Moghimi, Seven Steps To Successful Ultra-Low-Light Signal Conversion, Electronic Design, 2012-09-25

Ken Gentile and David Brandon, DDS Clocks To 3.5 GHz, Microwaves & RF, 2012-09-01

Eamon Nash and Ashraf Elghamrawi, RF Component Integration – Saving Space in High Performance Applications, High Frequency Electronics, 2012-09-18

John Ardizzoni, Great Expectations Come From Basic Understandings, Analog Dialogue, 2012-09-04

Webinars and Tutorials

Introduction to Analog RMS-to-DC Technology: Converters and Applications – This webinar provides users with a better understanding of the underlying theory of rms, and how rms-to-dc converters work.

The Fundamentals of Voltage References and Current Sensing - This webcast will discuss voltage references and how they are used in circuit design. It will also cover and compare reference designs, specifications, reference alternatives, and application ideas such as negative references, then present how currents are handled, measured, and generated in system design.

Precision basics: How not to be surprised by unexpected error sources - This webcast, co-sponsored by Avnet EM, presents error sources of a few fundamental front end signal conditioning blocks and provides hints for better practices that will save money and speed development time.

Fundamentals of Frequency Synthesis, Part 2: Direct Digital Synthesis (DDS) – This concludes our two-part series on frequency synthesis with an introduction to direct digital synthesis. We will give a basic review of how a direct digital synthesis system works, touching on the inner workings of the DDS engine at a relatively high level. We will also discuss the tradeoffs between PLL and DDS technology as a base choice for frequency synthesis needs.

Fundamentals of Frequency Synthesis, Part 1: Phase Locked Loops – The first of a two-part series on frequency synthesis, with an introduction to phase locked loops (PLLs). This webcast looks at the need for frequency generation; techniques from the past, present, and future; how to assess the performance of a frequency synthesizer; and real world applications. Particular attention will be focused on phase locked loops as frequency synthesizers.

Fundamentals of the RF Transmission and Reception of Digital Signals - Digital Modulation is an important topic for RF designers because most modern day transceivers transmit and receive digitally modulated data. In this webcast, part of ADI's continuing FUNDAMENTALS OF DESIGN series we will introduce you to the challenges—and solutions—for digital modulation. This webcast is a great way for beginners to get introduced to this vital communications standard or for veteran RF designers learn what's new in the field.

Fundamentals of Designing with Semiconductors: Beyond the Op Amp - This webcast, the third of our 12-part series on the Fundamentals of Designing with Semiconductors for Signal-Processing Applications, premieres March 9. It looks at Difference Amps, Instrumentation Amps, Log Amps, and other important amplifiers, and explains when to use each and how to select them for maximum circuit performance.

Fundamentals of Designing with Semiconductors for Signal Processing Applications: The Op Amp -- In this, the second webcast of our 12-part series, we look at the venerable op amp. What is it and how does it work? What are the different types of op amps and how do you select the right one for your circuit? This webcast will also explain offset, noise, bandwidth, and other specifications that impact amp operation, and how you can maximize your circuit's performance with the right op amp.

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