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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.

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.

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.

May 2014

CN-0350: 12-bit, 1-MSPS, Single-Supply, Two-Chip Data-Acquisition System for Piezoelectric Sensors

This 12-bit, 1-MSPS data-acquisition system uses only two active devices. The system processes charge input signals from piezoelectric sensors using a single 3.3-V supply and has a total error of less than 0.25% FSR after calibration over a 10C temperature range, making it ideal for a wide variety of laboratory and industrial measurements. The circuits small footprint makes this combination an industry-leading solution for data-acquisition systems where accuracy, speed, cost, and size play a critical role.

April 2014

CN0343: Ultrasonic Distance Measurement

This self-contained distance sensor utilizes an ultrasonic transmitter and sensitive analog receiver in conjunction with a precision analog microcontroller to provide distance measurements. Unlike complicated PLL-based receivers, the sensor uses a sensitive window comparator circuit, thereby minimizing real estate and cost. The approximate range is from 50 cm to 10 m with a resolution of about 2 cm. Temperature compensation is provided by the integrated temperature sensor and ADC contained in the microcontroller. For sensing the levels of thick liquids or foamy water, the ultrasonic level sensor is a better choice than capacitance, reed, or float sensors. In very dusty or corrosive environments, the ultrasonic sensor is the sensor of choice.

CN0304: Low Power DDS Waveform Generator

This 75-MHz low-power (25 mW total) direct digital synthesis (DDS) waveform generator includes an output buffer and anti-imaging filter to provide improved spectral performance, making it suitable for frequency generation or clocking applications requiring sine wave, triangular wave, and square outputs up to 18 MHz. As sampled data devices, low-power DDS devices must be followed by a suitable anti-imaging filter to remove spectral images, but their maximum current output is approximately 4 mA into a recommended 200-Ω load, so an op amp buffer at the DDS output is required to provide a low-impedance drive source for a high-quality 50-Ω filter. The combination of the DDS, output buffer, and seventh-order elliptic low pass filter provides high-quality spectral performance.

March 2014

CN0337: 12-Bit, 300 kSPS, Single-Supply, Fully Isolated RTD Temperature Measurement System with 3-Wire Compensation

This completely isolated 12-bit, 300-kSPS RTD temperature measuring system uses only three active devices to process the output of a Pt100 RTD. An innovative circuit provides lead-wire compensation using a standard 3-wire connection. The circuit operates on a single 3.3-V supply. The total error after room temperature calibration is less than 0.24% FSR for a 10C change in temperature, making it ideal for a wide variety of industrial temperature measurements. Both data and power are isolated, making the circuit robust to high voltages and ground-loop interference often encountered in harsh industrial environments.

CN0335: 12-Bit, 300 kSPS, Single-Supply, Fully Isolated, Data Acquisition System for 10 V Inputs

This completely isolated 12-bit, 300-kSPS data acquisition system uses only three active devices to process 10-V input signals using a single 3.3-V supply. The total error after room temperature calibration is less than 0.1% FSR over a 10C temperature change, making it ideal for a wide variety of industrial measurements. Both data and power are isolated, thereby making the circuit robust to high voltages and ground-loop interference often encountered in harsh industrial environments.

CN0314: Configurable 4-20 mA Loop Powered Transmitter/Receiver using a Micropower Instrumentation Amplifier

This configurable 4 mA-to-20 mA loop-powered transmitter is based on an industry-leading micropower instrumentation amplifier. Total unadjusted error is less than 1%. It can be configured with a single switch as either a transmitter that converts a differential input voltage into a current output, or as a receiver that converts a 4 mA-to-20 mA current input to a voltage output. Optimized for precision, low noise and low power industrial process control applications, the circuit can accept 0 V to 5V or 0 V to 10 V input range as a transmitter. As a receiver it can provide 0.2 V to 2.3 V or 0.2 V to 4.8 V output range compatible with ADCs using 2.5 V or 5 V references. The supply voltage can range from 12 V to 36 V as a transmitter and 7 V to 36 V as a receiver. The circuit is configurable, so a single hardware design can be used as a backup for both transmitter and receiver at the same time, minimizing inventory requirements.

February 2014

CN0336: 12-Bit, 300 kSPS, Single-Supply, Fully Isolated, Data Acquisition System for 4-20 mA Inputs

This completely isolated 12-bit, 300-kSPS data-acquisition system uses only three active devices to process 4-mA to 20-mA input signals using a single 3.3-V supply. The total error after room temperature calibration is 0.06% FSR over a 10C temperature range, making it ideal for a wide variety of industrial measurements. The small footprint makes it an industry-leading solution for 4-mA to 20-mA data acquisition systems where accuracy, speed, cost, and size play a critical role. Both data and power are isolated, making the circuit robust to high voltages and ground-loop interference often encountered in harsh industrial environments.

January 2014

CN0348: 16-Bit Single-Supply Buffered Voltage Output Digital-to Analog Conversion with Less Than 1 LSB Integral and Differential Nonlinearity

This complete single-supply,16-bit buffered voltage output DAC maintains 1 LSB integral and differential nonlinearity by utilizing a CMOS DAC followed by an innovative amplifier that has no crossover distortion. The circuit eliminates the crossover nonlinearity associated with most rail-to-rail op amps that can be as high as 4 LSBs to 5 LSBs in a 16-bit system. This industry leading solution is ideal for industrial process control and instrumentation applications that require a compact, single-supply, low-cost, highly linear 16-bit buffered voltage source. Total power dissipation for the three active devices is less than 25 mW typical when operating on a single 6-V supply.

CN0341: Magnetoresistive Linear Position Measurement

This contactless, anisotropic magnetoresistive (AMR) linear position measurement solution features 0.002-inch accuracy over a 0.5-inch range, making it ideal for applications where accurate, high-speed, non-contact length and position measurements are critical. It provides all the signal conditioning, including instrumentation amplifiers, buffers, and a 2-channel ADC, required to efficiently process the low-level AMR sensor bridge outputs. The result is an industry leading position measurement solution suitable for valve and flow measurement, machine tool speed control, motor speed measurement, and other industrial or automotive applications.

CN0332: Magnetoresistive (MR) Rotational Speed Sensor

This low-cost, high-speed, single-supply magnetoresistive (MR) signal conditioner features a minimum PCB footprint. The complete signal conditioning solution amplifies the small output voltage of the magnetoresistive sensor and converts it into a digital output signal with less than 5 ns rise and fall times and approximately 100-ps rms jitter. An excellent alternative to Hall effect sensors, the circuit provides a compact, cost effective, robust solution for high-speed rotational sensing in industrial and automotive applications.

 

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