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Circuits from the Lab

Circuits from the Lab reference circuits are engineered and tested for quick and easy system integration to help solve today's analog, mixed-signal, and RF design challenges.

July 2015

CN-0275: Complete Broadband Video-over-UTP Driver and Receiver Solution for RGB, YPbPr, and More

Originally intended to carry local area network (LAN) traffic, unshielded twisted pair (UTP) cable, such as Category-5e (Cat-5e), has become an economical solution in many other signal transmission applications because of its respectable performance and low cost. But impairments such as nonlinear bandlimiting due to the skin effect, low frequency flat loss, and delay skew from unequal twist rates must be considered. This circuit solution overcomes these impairments by using the AD8122 triple receiver/equalizer to restore the high frequency content of the video signals over UTP while also providing flat gain.

CN-0365: 16-Bit, 600 kSPS, Low Power Data Acquisition System for High Temperature Environments

A growing number of applications require data acquisition systems that must operate reliably at very high ambient temperature environments, such as downhole oil and gas drilling, avionics, and automotive. This circuit solution is a 16-bit, 600 kSPS successive approximation analog-to-digital converter (ADC) system using devices rated, characterized, and guaranteed at 175C.

May 2015

CN-0359: Fully Automatic High Performance Conductivity Measurement System

The circuit is a completely self-contained, microprocessor controlled, highly accurate conductivity measurement system ideal for measuring the ionic content of liquids, water quality analysis, industrial quality control, and chemical analysis. A carefully selected combination of precision signal conditioning components yields an accuracy of better than 0.3% over a conductivity range of 0.1 μS to 10 S (10 MΩ to 0.1 Ω) with no calibration requirements. The system accommodates 2- or 4-wire conductivity cells, and 2-, 3-, or 4-wire RTDs for added accuracy and flexibility.

CN-0373: Isolated USB to Isolated RS-485/Isolated RS-232 Interface

This circuit provides a completely isolated connection between the popular USB bus and an RS-485 or RS-232 bus. Both signal and power isolation ensures a safe USB device interface to an industrial bus or debug port, allowing TIA/EIA-485/232 bus traffic monitoring and the convenience of sending and receiving commands to and from a PC that is not equipped with an RS-485 or RS-232 port. Isolation in this circuit increases system safety and robustness in industrial and instrumentation applications by providing protection against electrical line surges and breaks the ground connection between bus and digital pins, thereby removing possible ground loops within the system.

March 2015

CN0371: Low Power LVDT Signal Conditioner with Synchronous Demodulation

This complete linear variable differential transformer (LVDT) signal conditioning circuit can accurately measure linear position or displacement from a mechanical reference. Synchronous demodulation in the analog domain extracts the position information and provides immunity to external noise. A 24-bit, Σ-Δ analog-to-digital converter (ADC) digitizes the position output for high accuracy. LVDTs utilize electromagnetic coupling between the movable core and the coil assembly. Contactless, frictionless operation is a primary reason for their use in aerospace, process controls, robotics, nuclear, chemical plants, hydraulics, power turbines, and other applications where operating environments can be hostile and long life and high reliability are required. The entire circuit, including the LVDT excitation signal, consumes only 10 mW. The excitation frequency and output data rates are SPI programmable. The bandwidth can be traded for dynamic range. Supporting bandwidths of over 1 kHz, the circuit has 100-dB dynamic range at 20 Hz, making it ideal for precision industrial position and gauging applications

CN-0368: Magnetoresistive Angle and Linear Position Measurements

This compact two-chip circuit provides a contactless anisotropic magnetoresistive (AMR) measurement solution ideal for either angle or linear position measurements. The two-chip system is capable of providing better than 0.2 angular accuracy over 180, and linear accuracy of 2 mil (0.002 inch) over a 0.5 inch range, depending on the size of the magnet used. The circuit is ideal for applications where high speed, accurate, noncontact angle and length measurements are critical, such as machine tool speed control, crane angle control, brushless dc motors, and other industrial or automotive applications.

January 2015

CN0375: Broadband Low Distortion Transmitter for 3G, 4G, and LTE Communication System

This RF transmitter utilizes the AD9142A TxDAC, ADRF6720 wideband I/Q modulator with integrated phase-locked loop (PLL) and voltage controlled oscillator (VCO), and ADL5320 -W driver amplifier. Signal biasing and scaling in the DAC-to-modulator interface circuit is controlled by four ground referenced resistors and two shunt resistors, respectively. The input and output matching on the ADL5320 driver amplifier is implemented using shunt capacitors at the input and the output.

CN0159: Universal Serial Bus (USB) Cable Isolator Circuit

This circuit isolates a peripheral device that already implements a USB interface. It is not possible to make a fully compliant bus-powered cable because there are no 100% efficient power converters to transfer the bus voltage across the barrier. In addition, the quiescent current of the converter does not comply with the standby current requirements of the USB standard. This is all in addition to the speed detection limitations of the ADuM4160. What can be achieved is a fixed speed or switch-controlled speed cable that can supply a modest power to the downstream peripheral. This custom application is not completely compliant with the USB standard.

December 2014

CN0364: PLC/DCS Quad Channel Voltage and Current Input with HART Compatibility

This complete, fully isolated, highly flexible, four-channel analog input system is suitable for programmable logic controller (PLC) and distributed control system (DCS) applications that require multiple voltage inputs and HART-compatible 4-mA to 20-mA current inputs. The analog input circuit, designed for group isolated industrial analog inputs, can support voltage and current input ranges including 5 V, 10 V, 0 V to 5 V, 0 V to 10 V, 4 mA to 20 mA, and 0 mA to 20 mA. The circuit is powered from a standard 24-V bus supply and generates an isolated 5-V system supply voltage.

CN0298: A Battery Powered Wireless Wind Speed and Wind Direction Data Acquisition System

This battery powered circuit uses an ADuCRF101 precision analog microcontroller with ARM Cortex-M3 processor and ISM-band RF transceiver to transmit wind speed and wind direction from a passive anemometer. The on-chip 12-bit analog-to-digital converter (ADC) and the wake-up timers acquire the wind direction and speed, respectively. In low-power hibernation mode, the ADuCRF101 draws 1.8 μA of supply current, resulting in long battery life, which is an important feature in wireless remote sensing applications. A single CR2032 Li-Ion battery can last 1 year to 2 years when operated in this mode.

November 2014

CN0342: Flyback Power Supply Using a High Stability Isolated Error Amplifier

This isolated flyback power supply uses a linear isolated error amplifier to supply the feedback signal from the secondary side to the primary side. Unlike optocoupler-based solutions, which have a nonlinear transfer function that changes over time and temperature, the linear transfer function of the isolated amplifier is stable and minimizes offset and gain errors when transferring the feedback signal across the isolation barrier. The entire circuit operates from 5 V to 24 V, allowing it to be used with standard industrial and automotive power supplies. The output capability of the circuit is up to 1 A with a 5-V input and 5-V output configuration. This solution can be adapted for applications where higher dc input voltages are used to create lower voltage isolated supplies with good efficiency and a small form factor. Examples include 10 W to 20 W telecommunication and server power supplies, where power efficiency and printed circuit board density are important and 48-V supplies are common.

CN0292: Completely Isolated, Robust, 4-Channel, Multiplexed Data Acquisition System for Industrial Level Signals

This robust, completely isolated industrial 4-channel data-acquisition system provides 16-bit noise-free code resolution, less than 15 ppm channel-to-channel crosstalk, and an up to 42-kSPS channel switching rate. The circuit acquires and digitizes industrial signal levels of 5 V, 10 V, 0 V to 10 V, and 0 mA to 20 mA. The input buffers provide overvoltage protection, thereby eliminating the leakage errors associated with conventional Schottky diode protection circuits. Applications for the circuit include process control (PLC/DCS modules), battery testing, scientific multichannel instrumentation, and chromatography.

October 2014

CN0366: A 40 GHz Microwave Power Meter with a Range from −30 dBm to +15 dBm

This accurate 40-GHz, microwave power meter with 45-dB range requires only two components. The RF detector uses an innovative detector cell composed of Schottky diodes followed by an analog linearization circuit. A low-power, 12-bit, 1-MSPS analog-to-digital converter (ADC) provides a digital output on a serial peripheral interface (SPI) port. After a simple calibration routine is run at the RF frequency of interest, the user can operate the system in measurement mode. The evaluation software displays the calibrated RF input power in units of dBm.

September 2014

CN0360: Frequency Selective, RMS Responding RF Detector with 90 dB Dynamic Range from 35 MHz to 4.4 GHz

This frequency selective, radio frequency (RF) detector offers a 90-dB detection range from 35 MHz to 4.4 GHz. Unlike a standalone detector that does not discriminate between signals in the frequency spectrum, this circuit can focus on a narrow band of frequencies, enhancing performance over the specified range. The rms responding circuit is stable vs. temperature and frequency, making it attractive for applications that require precise frequency control, selective RF power measurement, and strong immunity to unwanted blockers.

CN0355: Low Power, Temperature Compensated Bridge Signal Conditioner and Driver

This complete, low-power signal conditioner for bridge-type sensors includes a temperature compensation channel. Ideal for a variety of industrial pressure sensors and load cells that operate with drive voltages of between 5 V and 15 V, this circuit can process full-scale signals from approximately10 mV to 1 V using the internal programmable gain amplifier (PGA) of the 24-bit, sigma-delta (Σ-Δ) ADC. The entire circuit uses only three ICs and requires only 1 mA, excluding the bridge current. A ratiometric technique ensures accuracy and stability without a voltage reference.

July 2014

CN0357: Low Noise, Single-Supply, Toxic Gas Detector, Using an Electrochemical Sensor with Programmable Gain TIA for Rapid Prototyping

This single supply, low noise, portable gas detector, uses an Alphasense CO-AX electrochemical sensor to detect carbon monoxide. Electrochemical sensors offer several advantages for instruments that detect or measure the concentration of many toxic gases. Most sensors are gas specific and have usable resolutions under one part per million (ppm) of gas concentration. The circuit uses the ADA4528-2 dual auto-zero amplifier, which has a 2.5 V maximum offset voltage at room temperature and an industry leading 5.6 V/√Hz voltage noise density, and the AD5270-20 programmable rheostat, allowing for rapid prototyping of different gas sensor systems without changing the bill of materials. The ADR3412 precision, low noise, micropower reference establishes the 1.2 V common-mode, pseudo ground reference voltage with 0.1% accuracy and 8 ppm/C drift.

CN0328: Completely Isolated 4-Channel Multiplexed HART Analog Output Circuit

This circuit combines the AD5755-1 four-channel voltage and current output DAC with dynamic power control and the AD5700-1 HART modem, to impement a completely isolated multiplexed HART analog output solution. Power can be provided either from the transformer isolated power circuit provided on the board or from external power supplies connected to terminal blocks. This circuit is suitable for use in programmable logic controllers (PLCs) and distributed control system (DCS) modules that require multiple HART-compatible 4 mA to 20 mA current outputs, along with unipolar or bipolar voltage outputs. External transient protection circuitry is also included, which is important for applications located in harsh industrial environments.


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