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.

Bleed Current Improves Noise and Spurious Performance of PLL

AN-1154: Optimizing Phase Noise and Spur Performance of the ADF4157 and ADF4158 PLLs Using Constant Negative Bleed

The phase noise (PN) and integer boundary spur (IBS) performance of the ADF4157 and the ADF4158 fractional-N frequency synthesizers can be improved by activating a constant negative bleed current. The biggest improvement is achieved at frequencies close or equal to integer multiples of the phase-frequency-detector (PFD) frequency. This 5-page Application Note describes how to implement a bleed current and measure its effects.

Impedance-Matched Filter Balun Boosts Performance of RF Transceivers

AN-1151: Using a Johanson 2450BM14E0007 Impedance-Matched, Integrated Filter Balun with the ADF7241 and ADF7242

This 6-page Application Note describes the use and performance achieved by the Johanson Technology, Inc., 2450BM14E0007 impedance-matched (complex differential impedance value) filter balun with the ADF7241 or ADF7242 2.4-GHz RF transceivers. The filter balun effectively reduces the RF front-end component count and layout space. This balun is 100% RF tested by Johanson Technology. Additional Information provides insight into how harmonic emissions are attenuated and further details about the balun.

Circuits from the Lab

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.

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

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.

March 2013

1.65-GHz Clock Fanout Buffer includes frequency dividers and phase shifters

The AD9508 clock buffer, designed for high-speed, low-jitter applications, accepts one single-ended or differential input clock and provides up to four differential LVDS/HSTL output clocks at up to 1.65 GHz or eight single-ended 1.8-V CMOS output clocks at up to 250 MHz. Each output can be divided by any integer up to 1024, and coarse phase adjustments can be made between the outputs. Pin strapping allows various configurations to be set at power up without the need for SPI or I²C programming. Operating with a 2.375-V to 3.465-V supply, the AD9508 draws 185 mA with HSTL outputs, 152 mA with LVDS outputs, 141 mA with CMOS outputs, and 6 mA in power-down mode. Specified from –40°C to +85°C, it is available in a 24-lead LFCSP package and priced at $4.25 in 1000s.

Low-cost Logarithmic Converter features 160-dB range

The ADL5303 logarithmic detector is optimized to measure low-frequency signal power in fiber optic systems. Providing 160-dB dynamic range (100 pA to 10 mA), it achieves 0.1-dB log conformance from 1 nA to 1 mA. The laser-trimmed log slope of 10 mV/dB (200 mV/decade) can be adjusted to fit the available span, and an on-chip reference allows the intercept to be repositioned. An adaptive biasing scheme reduces photodiode dark current at very low light levels. The bandwidth, which is proportional to the input current, increases from 2 kHz at 1 nA to a maximum of 10 MHz. Operating with a 3.0-V to 5.5-V supply, the ADL5303 draws 45 mA in normal mode and 60 µA when disabled. Specified from –40°C to +85°C, it is available in a 16-lead LFCSP package and priced at $4.47 in 1000s.

Technical Articles

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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