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Engineer-to-Engineer and Application Notes These engineer-to-engineer and application notes, published within the past 12 months, are listed in chronological order. April 2013 AN-1181: Using a MEMS Microphone in a 2-Wire Microphone Circuit MEMS microphones are being used to replace electret condenser microphones (ECMs) in audio circuits. These two types of microphones perform the same function, but the connection between the microphone and the rest of the system is different for ECMs and MEMS microphones. This 2-page Application Note explains those differences and provides design details for a simple MEMS microphone based replacement circuit. March 2013 AN-1187: Radiated Immunity Performance of the AD7780 in Weigh Scale Applications The AD7780 low-noise, low-power, 24-bit sigma-delta analog-to-digital converter with integrated PGA is used in low- to mid-end weigh scale systems. The radiated immunity of the system is tested as part of the release process. This 12-page Application Note describes how to achieve the best radiated immunity performance from the AD7780, taking into account the effects of layout and component placement when designing a printed circuit board (PCB). The radiated immunity testing is performed on the complete system (ADC, PCB, and load cell) as per standard IEC 61000-4-3. 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-1180: Optimizing Video Platforms for Automated Post-Production Self-Tests This 10-page Application Note describes techniques to use for post-production testing and debugging of video platforms using advanced video (ADV) series devices. Advanced video systems are becoming more complex and the video chains contain more and more links. Employing built-in self-tests on video evaluation systems allows a significant increase in productivity by automated tests. The ADV parts include features that allow finding a short, an open, or a problem in video processing, audio processing, or data/control circuitry. Many of ADV parts contain internal pattern generators, synchronization detection circuitry (for video), and built-in external memory tests that can be used to test a platform and facilitate the process of debugging a potentially faulty platform. To test the system, the final video processing circuitry must contain a microprocessor that includes a connection to tested video parts and a postproduction program that can be enabled and run at least once after production. February 2013 AN-1178: AD7292 DAC Disable Function Timing The AD7292 monitor and control IC contains all the functionality required for general-purpose monitoring of analog signals and control of external devices, including an 8‑channel multiplexer, 10-bit SAR ADC, four 10-bit DACs, a ±1°C accurate internal temperature sensor, and 12 GPIOs to aid system monitoring and control. The DAC has an output voltage range up to 5 V (LSB of 4.88 mV). The output buffer can be controlled via software or hardware. This 4-page Application Note describes the timing associated with the DAC disable function. January 2013 AN-1169: Linear Gain Setting Mode: A Detailed Description A digital potentiometer (digiPOT) is commonly used to set an amplifier's gain or a regulator's output voltage. In each case, the transfer function depends on two resistances. When a digiPOT is used to replace these resistances, the transfer function becomes logarithmic. This behavior can be desirable in some applications, such as audio, but a linear transfer function is preferred in many applications. This 4-page Application Note presents three different methods for achieving a linear output. December 2012 AN-1166: HDMI Sink Jitter Tolerance Issues for Devices that Use an HDMI Mux and HDMI Receiver An HDMI mux is commonly used to increase the number of HDMI inputs in a system, but this results in two cascaded stages that handle the TMDS signals before they are digitally processed in the receiver. Each stage contributes jitter that degrades the quality of the signal. This can present a challenge for HDMI compliance tests, especially when operating at higher data rates. This 2-page Application Note shows how a synchronous mux can perform better because it removes most types of jitter and presents a clean signal to the HDMI receiver. November 2012 AN-1171: Calibrating a Single-Phase Energy Meter Based on the ADE7880 This 15-page Application Note describes the calibration procedure for the ADE7880 high-accuracy, 3-phase electrical energy measurement IC, including equations and examples of how to calculate each constant. The ADE7880 incorporates second-order sigma-delta (Σ-Δ) analog-to-digital converters, a digital integrator, reference circuitry, and all of the signal processing required to measure the total (fundamental and harmonic) active and apparent energy and the fundamental-only active and reactive energy. In addition, it computes the rms of harmonics on the phase and neutral currents and on the phase voltages; the active, reactive, and apparent power; the power factor; and the harmonic distortion on each harmonic for all phases; and the total harmonic distortion plus noise (THD + N) for all currents and voltages. This 6-page Application Note describes how to use the ADP2384/ADP2386 4-A/6-A synchronous, step-down, dc-to-dc regulators in a synchronous, inverting buck-boost topology to generate negative output voltages from positive input power supplies, without increasing the cost, component count, or solution size. The synchronous topology provides higher efficiency with low output voltages and lower noise under light-load operation. September 2012 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. AN-1160: Cortex-M3 Based ADuCxxx Serial Download Protocol A key feature of the Cortex-M3 based ADuCxxx is their ability to download code on-chip Flash/EE program memory while in-circuit. The download, conducted over the UART port, is commonly referred to as a serial download. This Application Note details the Cortex-M3 based ADuCxxx device serial download protocol, allowing end users to understand and successfully implement this protocol (embedded host to embedded Cortex-M3 based ADuCxxx device) in an end-target system. This Application Note describes the hardware master and slave implementation of an I2C-compatible interface using the ADuCxxx family of Cortex-M3 based precision microcontrollers from Analog Devices. It includes example code showing how master and slave can communicate with each other using the I2C interface. These examples are: master transmit and receive; slave transmit and receive; DMA transfers (transmit and receive) in slave mode; and DMA transfers (transmit and receive) in master mode. August 2012 AN-1135: ADC Sampling Information ADM1275/ADM1276/ADM1075 The ADM1275, ADM1276, and ADM1075 hot-swap controllers share the same basic analog-to-digital converter (ADC) core and PMBus interface, but they have some subtle differences with regard to averaging calculations, ADC register updates, and data readback. This 4-page Application Note describes the ADC operation and how to maximize the data rate. July 2012 Kalman Filter Estimates Orientation Angles Based on Sensor Data AN-1157: Tuning the Extended Kalman Filter in the ADIS16480 The ADIS16480 MEMS inertial measurement unit (IMU) includes a 3-axis accelerometer, a 3-axis gyroscope, a 3-axis magnetometer, and a barometer. It also includes an extended Kalman filter (EKF) that computes dynamic orientation angles. The EKF estimates the orientation angles using a combination of gyroscope, accelerometer, and magnetometer contributions, with real-time filter weighting factors determined by covariance terms representing the level of uncertainty assigned to each sensor. Optimal performance comes from selecting appropriate covariance values for the sensors, given the application environment. This 8-page Application Note offers analytical tools for simplifying this process. May 2012 Bleed Current Improves Noise and Spurious Performance of PLL 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. Simple Calibration Procedure Improves Performance of Energy Meter AN-1152: Calibrating a Single-Phase Energy Meter Based on the ADE7816 This 9-page Application Note describes how to calibrate the ADE7816 energy metering IC, including equations and examples of how to calculate each constant. The ADE7816 is a high-accuracy multichannel metering IC that can measure the energy on up to six current channels. It provides a variety of energy measurements including active and reactive energy, along with rms current and voltage readings—and a variety of power quality features, including no load, reverse power, and angle measurement. The data can be accessed via SPI, I2C, or high-speed data-capture (HSDC) interfaces. Impedance-Matched Filter Balun Boosts Performance of RF Transceivers 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.
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