Analog Devices Inc./Maxim Integrated

The AD684 is a monolithic quad sample-and-hold amplifier (SHA). It features four complete sampling channels, each controlled by an independent hold command. Each SHA is complete with an internal hold capacitor. The high accuracy SHA channels are self-contained and require no external components or adjustments. The AD684 is manufactured on a BiMOS process which provides a merger of high performance bipolar circuitry and low power CMOS logic.The AD684 is ideal for high performance, multichannel data acquisition systems. Each SHA channel can acquire a signal in less than 1 µs and retain the held value with a droop rate of less than 0.01 µV/µs. Excellent linearity and ac performance make the AD684 an ideal front end for high speed 12- and 14-bit ADCs.The AD684 has a self-correcting architecture that minimizes hold mode errors and insures accuracy over temperature. Each channel of the AD684 is capable of sourcing 5 mA and incorporates output short circuit protection.The AD684 is specified for three temperature ranges. The J grade device is specified for operation from 0 to +70°C, the A grade from -40°C to +85°C and the S grade from -55°C to +125°C.

The AD694 is a monolithic current transmitter that accepts high level signal inputs to drive a standard 4-20 mA current loop for the control of valves, actuators, and other devices commonly used in process control. The input signal is buffered by an input amplifier that can be used to scale the input signal or buffer the output from a current mode DAC. Precalibrated input spans of 0 V to 2 V and 0 V to 10 V are selected by simple pin strapping; other spans may be programmed with external resistor.The output stage compliance extends to within 2 V of VS and its special design allows the output voltage to extend below common in dual supply operation. An alarm warns of an open 4-to-20 mA loop or noncompliance of the output stage.Active laser trimming of the AD694's thin film resistors results in high levels of accuracy without the need for additional adjustments and calibration. An external pass transistor may be used with the AD694 to off-load power dissipation, extending the temperature range of operation.The AD694 is the ideal building block for systems requiring noise immune 4-20 mA signal transmission to operate valves, actuators, and other control devices, as well as for the transmission of process parameters such as pressure, temperature, or flow. It is recommended as a replacement for discrete designs in a variety of applications in industrial process control, factory automation, and system monitoring.The AD694 is available in hermetically sealed, 16-pin CERDIP and plastic SOIC, specified over the -40°C to +85°C industrial temperature range, and in a 16-pin plastic DIP, specified over the 0°C to +70°C temperature range.

The AD698 is a complete, monolithic Linear Variable Differential Transformer (LVDT) signal conditioning subsystem. It is used in conjunction with LVDTs to convert transducer mechanical position to a unipolar or bipolar dc voltage with a high degree of accuracy and repeatability. All circuit functions are included on the chip. With the addition of a few external passive components to set frequency and gain, the AD698 converts the raw LVDT output to a scaled dc signal. The device will operate with half-bridge LVDTs, LVDTs connected in the series opposed configuration (4-wire), and RVDTs.The AD698 contains a low distortion sine wave oscillator to drive the LVDT primary. Two synchronous demodulation channels of the AD698 are used to detect primary and secondary amplitude. The part divides the output of the secondary by the amplitude of the primary and multiplies by a scale factor. This eliminates scale factor errors due to drift in the amplitude of the primary drive, improving temperature performance and stability.The AD698 uses a unique ratiometric architecture to eliminate several of the disadvantages associated with traditional approaches to LVDT interfacing. The benefits of this new circuit are: no adjustments are necessary; temperature stability is improved; and transducer interchangeability is improved.

The AD704 is a quad, low power bipolar op amp that has the low input bias current of a BiFET amplifier and offers a significantly lower IBdrift over temperature. It uses superbeta bipolar input transistors to achieve picoampere input bias current levels (similar to FET input amplifiers at room temperature), while its IB typically increases only by 5× at 125°C (unlike a BiFET amp, for which IB doubles every 10°C, resulting in a 1000× increase at 125°C). In addition, the AD704 achieves 150 μV offset voltage and the low noise characteristics of a precision bipolar input op amp.Because it has only 1/20 the input bias current of an OP07, the AD704 does not require the commonly used balancing resistor. Furthermore, the current noise is 1/5 that of the OP07, which makes the AD704 usable with much higher source impedances. At 1/6 the supply current (per amplifier) of the OP07, the AD704 is better suited for today’s higher density circuit boards and battery-powered applications.The AD704 is an excellent choice for use in low frequency active filters in 12- and 14-bit data acquisition systems, in precision instrumentation, and as a high quality integrator. The AD704 is internally compensated for unity gain stability. The AD704J is rated over the commercial temperature range of 0°C to 70°C. The AD704A is rated over the industrial temperature of −40°C to +85°C. The AD704S is rated over the military temperature range of −55°C to +125°C, processed to MIL-STD-883B.APPLICATIONSIndustrial/process controlsWeigh scalesECG/EKG instrumentationLow frequency active filters