Impedance Measurement and Analysis
Featured Products (11)
The AD4003/AD4007/AD4011 are high accuracy, high speed, low power, 18-bit, Easy Drive, precision successive approximation register (SAR) analog-to-digital converters (ADCs). The high throughput allows both accurate capture of high frequency signals and decimation to achieve higher SNR, while also reducing antialiasing filter challenges.
Easy Drive features reduce signal chain complexity and power consumption, and enable higher channel density. The reduced input current, particularly in high-Z mode, coupled with a long signal acquisition phase, eliminates the need for a dedicated high power, high speed ADC driver, which broadens the range of low power precision amplifiers that can drive these ADCs directly (see Figure 2). The input span compression feature enables the ADC driver amplifier and the ADC to operate off common supply rails without the need for a negative supply while preserving the full ADC code range. The input overvoltage clamp protects the ADC inputs against overvoltages, minimizes disturbance on the reference pin, and eliminates the need for external protection diodes.
The low serial peripheral interface (SPI) clock rate (75 MHz for the AD4003 in turbo mode) reduces the digital input/output power consumption, broadens processor options, and simplifies the task of sending data across digital isolation.
The SPI-compatible versatile serial interface features seven different programmable modes with an optional busy indicator. Using the SDI input, several ADCs can be daisy-chained on a single 3-wire bus. The AD4003/AD4007/AD4011 are compatible with 1.8 V, 2.5 V, 3 V, and 5 V logic, using the separate supply, VIO.
- Automatic test equipment
- Machine automation
- Medical equipment
- Battery-powered equipment
- Precision data acquisition systems
The LTC2387-18 is a low noise, high speed, 18-bit 15Msps successive approximation register (SAR) ADC ideally suited for a wide range of applications. The combination of excellent linearity and wide dynamic range makes the LTC2387-18 ideal for high speed imaging and instrumentation applications. No latency operation provides a unique solution for high speed control loop applications. The very low distortion at high input frequencies enables communications applications requiring wide dynamic range and significant signal bandwidth.
To support high speed operation while minimizing the number of data lines, the LTC2387-18 features a serial LVDS digital interface. The LVDS interface has one-lane and two-lane output modes, allowing the user to optimize the interface data rate for each application.
- High Speed Data Acquisition
- Control Loops
The AD5683R/AD5682R/AD5681R/AD5683, members of the nanoDAC+® family, are low power, single-channel, 16-/14-/12-bit buffered voltage out digital-to-analog converters (DACs). The devices, except the AD5683, include an enabled by default internal 2.5 V reference, offering 2 ppm/°C drift. The output span can be programmed to be 0 V to VREF or 0 V to 2 × VREF. All devices operate from a single 2.7 V to 5.5 V supply and are guaranteed monotonic by design. The devices are available in a 2.00 mm × 2.00 mm, 8-lead LFCSP or a 10-lead MSOP.
The internal power-on reset circuit ensures that the DAC register is written to zero scale at power-up while the internal output buffer is configured in normal mode. The AD5683R/AD5682R/AD5681R/AD5683 contain a power-down mode that reduces the current consumption of the device to 2 µA (maximum) at 5 V and provides software selectable output loads while in power-down mode.
The AD5683R/AD5682R/AD5681R/AD5683 use a versatile 3-wire serial interface that operates at clock rates of up to 50 MHz. Some devices also include asynchronous RESET pin and VLOGIC pin options, allowing 1.8 V compatibility
- High Relative Accuracy (INL).
AD5683R/AD5683 (16-bit): ±2 LSB maximum.
- Low Drift, 2.5 V On-Chip Reference.
2 ppm/°C typical temperature coefficient.
5 ppm/°C maximum temperature coefficient.
- Two Package Options.
2.00 mm × 2.00 mm, 8-lead LFCSP.
- Process controls
- Data acquisition systems
- Digital gain and offset adjustment
- Programmable voltage sources
The AD9834 is a 75 MHz low power DDS device capable of producing high performance sine and triangular outputs. It also has an on-board comparator that allows a square wave to be produced for clock generation. Consuming only 20 mW of power at 3 V makes the AD9834 an ideal candidate for power-sensitive applications.
Capability for phase modulation and frequency modulation is provided. The frequency registers are 28 bits; with a 75 MHz clock rate, resolution of 0.28 Hz can be achieved. Similarly, with a 1 MHz clock rate, the AD9834 can be tuned to 0.004 Hz resolution. Frequency and phase modulation are affected by loading registers through the serial interface and toggling the registers using software or the FSELECT pin and PSELECT pin, respectively.
The AD9834 is written to using a 3-wire serial interface. This serial interface operates at clock rates up to 40 MHz and is compatible with DSP and microcontroller standards.
The device operates with a power supply from 2.3 V to 5.5 V. The analog and digital sections are independent and can be run from different power supplies, for example, AVDD can equal 5 V with DVDD equal to 3 V.
The AD9834 has a power-down pin (SLEEP) that allows external control of the power-down mode. Sections of the device that are not being used can be powered down to minimize the current consumption. For example, the DAC can be powered down when a clock output is being generated.
The part is available in a 20-lead TSSOP.
- Frequency stimulus/waveform generation
- Frequency phase tuning and modulation
- Low power RF/communications systems
- Liquid and gas flow measurement
- Sensory applications: proximity, motion, and defect detection
- Test and medical equipment
The ADA4870 is a unity gain stable, high speed current feedback amplifier capable of delivering 1 A of output current and 2500 V/μs slew rate from a 40 V supply. Manufactured using the Analog Devices, Inc., proprietary high voltage extra fast complementary bipolar (XFCB) process, the innovative architecture of the ADA4870 enables high output power, high speed signal processing solutions in applications that require driving a low impedance load.
The ADA4870 is ideal for driving high voltage power FETs, piezo transducers, PIN diodes, CCD panels, and a variety of other demanding applications that require high speed from high supply voltage at high output current.
The ADA4870 is available in a power SOIC package (PSOP_3), featuring an exposed thermal slug that provides high thermal conductivity, enabling efficient heat transfer for improved perfor-mance and reliability in demanding applications. The ADA4870 operates over the industrial temperature range (−40°C to +85°C).
- Envelope tracking
- Power FET driver
- Piezo drivers
- PIN diode drivers
- Waveform generation
- Automated test equipment (ATE)
- CCD panel drivers
- Composite amplifiers
The ADA4817-1 (single) and ADA4817-2 (dual) FastFET™ amplifiers are unity-gain stable, ultrahigh speed, voltage feedback amplifiers with FET inputs. These amplifiers were developed with the Analog Devices, Inc., proprietary eXtra fast complementary bipolar (XFCB) process, which allows the amplifiers to achieve ultralow noise (4 nV/√Hz; 2.5 fA/√Hz) as well as very high input impedances.
With 1.3 pF of input capacitance, low noise (4 nV/√Hz), low offset voltage (2 mV maximum), and 1050 MHz −3 dB bandwidth, the ADA4817-1/ADA4817-2 are ideal for data acquisition front ends as well as wideband transimpedance applications, such as photodiode preamps.
With a wide supply voltage range from 5 V to 10 V and the ability to operate on either single or dual supplies, the ADA4817-1/ADA4817-2 are designed to work in a variety of applications including active filtering and analog-to-digital converter (ADC) driving. The ADA4817-1 is available in a 3 mm × 3 mm, 8-lead LFCSP and 8-lead SOIC, and the ADA4817-2 is available in a 4 mm × 4 mm, 16-lead LFCSP. These packages feature a low distortion pinout that improves second harmonic distortion and simplifies circuit board layout. They also feature an exposed pad that provides a low thermal resistance path to the printed circuit board (PCB). The EPAD enables more efficient heat transfer and increases reliability. These products are rated to work over the extended industrial temperature range (−40°C to +105°C).
- Photodiode amplifiers
- Data acquisition front ends
- ADC drivers
- Output buffers
Security and Surveillance
- Scanning Equipment
The LTM8049 is a Dual SEPIC/Inverting μModule® (power module) DC/DC Converter. Each of the two outputs can be easily configured as a SEPIC or Inverting converter by simply grounding the appropriate output rail. The LTM8049 includes power devices, inductors, control circuitry and passive components. All that is needed to complete the design are input and output caps, and small resistors to set the output voltages and switching frequency. Other components may be used to control the soft-start and undervoltage lockout.
The LTM8049 is packaged in a thermally enhanced, compact (15mm × 9mm) over-molded Ball Grid Array (BGA) package suitable for automated assembly by standard surface mount equipment. The LTM8049 is RoHS compliant.
- Battery Powered Regulator
- Local Negative Voltage Regulator
- Low Noise Amplifier Power
The AD5933 is a high precision impedance converter system solution that combines an on-board frequency generator with a 12-bit, 1 MSPS, analog-to-digital converter (ADC). The frequency generator allows an external complex impedance to be excited with a known frequency. The response signal from the impedance is sampled by the on-board ADC and a discrete Fourier transform (DFT) is processed by an on-board DSP engine. The DFT algorithm returns a real (R) and imaginary (I) data-word at each output frequency.
Once calibrated, the magnitude of the impedance and relative phase of the impedance at each frequency point along the sweep is easily calculated. This is done off chip using the real and imaginary register contents, which can be read from the serial I2C interface.
A similar device, also available from Analog Devices, Inc., is the AD5934, a 2.7 V to 5.5 V, 250 kSPS, 12-bit impedance converter, with an internal temperature sensor and is packaged in a 16-lead SSOP
- Electrochemical analysis
- Bioelectrical impedance analysis
- Impedance spectroscopy
- Complex impedance measurement
- Corrosion monitoring and protection equipment
- Biomedical and automotive sensors
- Proximity sensing
- Nondestructive testing
- Material property analysis
- Fuel/battery cell condition monitoring
The ADuCM350 is a configurable Impedance Converter and Potentiostat with current and voltage measurement capability for both Electrochemical sensors and Biosensors. It is a complete, coin cell powered, high precision, MCU integrated solution for portable device applications such as point-of-care diagnostics and body-worn devices for monitoring vital signs.
The ADuCM350 analog front end (AFE) features a 16-bit, precision, 160 kSPS analog-to-digital converter (ADC); 0.17% precision voltage reference; 12-bit, no missing codes digital-to-analog converter (DAC); and a reconfigurable ultralow leakage switch matrix. It has 4 voltage measurement channels, up to 8 current measurement channels and an impedance measurement DFT engine. The ADuCM350 also includes an ARM Cortex-M3-based processor, memory, and all I/O connectivity to support portable meters with display, USB communication, and active sensors. The ADuCM350 is available in a 120-lead, 8 mm × 8 mm CSP_BGA and operates from −40°C to +85°C.
To support extremely low dynamic and hibernate power management, the ADuCM350 provides a collection of power modes and features, such as dynamic and software controlled clock gating and power gating. The AFE is connected to the ARM Cortex-M3 via an advanced high performance bus (AHPB) slave interface on the advanced microcontroller bus architecture (AMBA) matrix, as well as direct memory access (DMA) and interrupt connections.
- Point-of-care diagnostics
- Body-worn devices for monitoring vital signs
- Amperometric, voltametric, and impedometric measurements
The AD9958 consists of two DDS cores that provide independent frequency, phase, and amplitude control on each channel. This flexibility can be used to correct imbalances between signals due to analog processing, such as filtering, amplification, or PCB layout related mismatches. Because both channels share a common system clock, they are inherently synchronized. Synchronization of multiple devices is supported.
The AD9958 can perform up to a 16-level modulation of frequency, phase, or amplitude (FSK, PSK, ASK). Modulation is performed by applying data to the profile pins. In addition, the AD9958 also supports linear sweep of frequency, phase, or amplitude for applications such as radar and instrumentation.
The AD9958 serial I/O port offers multiple configurations to provide significant flexibility. The serial I/O port offers an SPIcompatible mode of operation that is virtually identical to the SPI operation found in earlier Analog Devices, Inc., DDS products. Flexibility is provided by four data pins (SDIO_0 / SDIO_1 / SDIO_2 / SDIO_3) that allow four programmable modes of serial I/O operation.
The AD9958 uses advanced DDS technology that provides low power dissipation with high performance. The device incorporates two integrated, high speed 10-bit DACs with excellent wideband and narrow-band SFDR. Each channel has a dedicated 32-bit frequency tuning word, 14 bits of phase offset, and a 10-bit output scale multiplier.
The DAC outputs are supply referenced and must be terminated into AVDD by a resistor or an AVDD center-tapped transformer. Each DAC has its own programmable reference to enable different full-scale currents for each channel.
The DDS acts as a high resolution frequency divider with the REFCLK as the input and the DAC providing the output. The REFCLK input source is common to both channels and can be driven directly or used in combination with an integrated REFCLK multiplier (PLL) up to a maximum of 500 MSPS. The PLL multiplication factor is programmable from 4 to 20, in integer steps. The REFCLK input also features an oscillator circuit to support an external crystal as the REFCLK source. The crystal must be between 20 MHz and 30 MHz. The crystal can be used in combination with the REFCLK multiplier.
The AD9958 comes in a space-saving 56-lead LFCSP package. The DDS core (AVDD and DVDD pins) is powered by a 1.8 V supply. The digital I/O interface (SPI) operates at 3.3 V and requires the pin labeled DVDD_I/O (Pin 49) be connected to 3.3 V.
The AD9958 operates over the industrial temperature range of −40°C to +85°C.
- Agile local oscillators
- Phased array radars/sonars
- Synchronized clocking
- RF source for AOTF
- Single-side band suppressed carriers
- Quadrature communications
The AD8302 is a fully integrated system for measuring gain/loss and phase in numerous receive, transmit, and instrumentation applications. It requires few external components and a single supply of 2.7 V–5.5 V. The ac-coupled input signals can range from –60 dBm to 0 dBm in a 50 Ω system, from low frequencies up to 2.7 GHz. The outputs provide an accurate measurement of either gain or loss over a ±30 dB range scaled to 30 mV/dB, and of phase over a 0°–180° range scaled to 10 mV/degree. Both subsystems have an output bandwidth of 30 MHz, which may optionally be reduced by the addition of external filter capacitors. The AD8302 can be used in controller mode to force the gain and phase of a signal chain toward predetermined setpoints.
The AD8302 comprises a closely matched pair of demodulating logarithmic amplifiers, each having a 60 dB measurement range. By taking the difference of their outputs, a measurement of the magnitude ratio or gain between the two input signals is available. These signals may even be at different frequencies, allowing the measurement of conversion gain or loss. The AD8302 may be used to determine absolute signal level by applying the unknown signal to one input and a calibrated ac reference signal to the other. With the output stage feedback connection disabled, a comparator may be realized, using the setpoint pins MSET and PSET to program the thresholds.
The signal inputs are single-ended, allowing them to be matched and connected directly to a directional coupler. Their input impedance is nominally 3 kΩ at low frequencies.
The AD8302 includes a phase detector of the multiplier type, but with precise phase balance driven by the fully limited signals appearing at the outputs of the two logarithmic amplifiers. Thus, the phase accuracy measurement is independent of signal level over a wide range.
The phase and gain output voltages are simultaneously available at loadable ground referenced outputs over the standard output range of 0 V to 1.8 V. The output drivers can source or sink up to 8 mA. A loadable, stable reference voltage of 1.8 V is available for precise repositioning of the output range by the user.
In controller applications, the connection between the gain output pin VMAG and the setpoint control pin MSET is broken. The desired setpoint is presented to MSET and the VMAG control signal drives an appropriate external variable gain device. Likewise, the feedback path between the phase output pin VPHS and its setpoint control pin PSET may be broken to allow operation as a phase controller.
The AD8302 is fabricated on Analog Devices’ proprietary, high performance 25 GHz SOI complementary bipolar IC process. It is available in a 14-lead TSSOP package and operates over a –40°C to +85°C temperature range. An evaluation board is available.
Interactive Signal Chains
The circuit shown in Figure 1 yields accurate impedance measurements extending from the low ohm range to several hundred kΩ and also optimizes the overall accuracy of the AD5933/AD5934.
Figure 1. Optimized Signal Chain for Impedance Measurement Accuracy (Simplified Schematic, All Connections and Decoupling Not Shown)
UG-1201 describes the evaluation board for the ADA4625-1 low noise, fast settling, single supply, rail-to-rail output (RRO), junction field effect transistor (JFET) op amp in an 8-lead small outline integrated circuit (SOIC) package with an exposed pad. The design of this evaluation board emphasizes simplicity and ease of use. This evaluation board is a 2-layer board that accommodates edge mounted SubMiniature version A (SMA) connectors on the inputs and outputs. The SMA connectors allow efficient connection to test equipment or other circuitry.
The evaluation board ground plane, components placement, and power supply bypassing are optimized for maximum circuit flexibility and performance. The exposed pad of the ADA4625-1 is connected to the ground plane on the evaluation board to enhance thermal and noise performance. The evaluation board uses a combination of surface mount technology (SMT) component case sizes 0603 and 0805, with the exception of the bypass capacitors, Capacitor C3 and Capacitor C5, which have a maximum standard size of 1206. The evaluation board also features a variety of unpopulated resistor and capacitor pads, which provide the user with multiple choices and extensive flexibility for different application circuits and configurations, such as active loop filters, transimpedance amplifiers (TIAs), and charge amplifiers.
The ADA4625-1 data sheet covers the specifications and details of the device operation and application circuit configurations and guidance. Consult the data sheet in conjunction with UG-1201 for a better understanding of the device operation, especially when powering up the evaluation board for the first time.
Product Selection Guide
- AN-1302: Optimizing the ADuCM350 for 4-Wire, BioIsolated Impedance Measurement Applications (Rev. A) PDF
- AN-756: Sampled Systems and the Effects of Clock Phase Noise and Jitter (Rev. 0) PDF
- AN-931: Understanding PulSAR ADC Support Circuitry (Rev. 0) PDF
- AN-202: An IC Amplifier User’s Guide to Decoupling, Grounding, and Making Things Go Right for a Change (Rev. B) PDF
- AN-847: Measuring a Grounded Impedance Profile Using the AD5933 (Rev. A) PDF