Part Details for AD7887 by Analog Devices Inc

The RF signal being measured is applied to the AD8318. The device is configured in its so-called measurement mode, with the VSET and VOUT pins connected together. In this mode, the output voltage vs. the input signal level is linear-in-dB (nominally −24 mV/dB) and has a typical output voltage range of 0.5 V to 2.1 V.

The circuit, shown in Figure 1, incorporates a dual axis ADXL203 accelerometer and the AD7887 12-bit successive approximation (SAR) ADC to create a dual axis tilt measurement system.<p>The ADXL203 is a polysilicon surface micromachined sensor and signal conditioning circuit. Acceleration in the X or Y axis will produce a corresponding output voltage on the XOUT or YOUT output pins of the device. The X axis and Y axis are perpendicular to one another. The AD8608 quad op amp buffers, attenuates, and level shifts the ADXL203 outputs so they are at the proper levels to drive the inputs of the AD7887. The rail-to-rail input/output AD8608 is chosen for its low offset voltage (65 μV maximum), low bias current (1 pA maximum), low noise (8 nV/√Hz), and small footprint (14-lead SOIC or TSSOP).<p>The AD7887 is configurable for either dual or single channel operation via the on-chip control register. In this application it is configured for dual channel mode, allowing the user to monitor both outputs of the ADXL203, thereby providing a more accurate and complete solution.<p>The system maintains an accuracy of 1° over 90° and over temperature. The circuit provides this precision, performance, and range in a low cost, low power, small footprint, calibration dependent solution. The ADXL203 is specified over a minimum temperature range of −40°C to +105°C and is available in an 8-terminal ceramic leadless chip carrier package (LCC).