24-Bit, 156 kSPS, 112 dB Sigma-Delta ADC with On-Chip Buffers and Serial Interface

The AD7765 is a high performance, 24-bit sigma-delta (Σ-Δ) analog-to-digital converter (ADC). It combines wide input bandwidth, high speed, and performance of 112 dB dynamic range at a 156 kHz output data rate. With excellent dc specifications, the converter is ideal for high speed data acquisition of ac signals where dc data is also required.

Using the AD7765 eases front-end antialias filtering requirements, simplifying the design process significantly. The AD7765 offers pin-selectable decimation rates of 128× and 256×. Other features include an integrated buffer to drive the reference, as well as a fully differential amplifier to buffer and level shift the input to the modulator.

An overrange alert pin indicates when an input signal exceeds the acceptable range. The addition of internal gain and internal overrange registers makes the AD7765 a compact, highly integrated data acquisition device requiring minimal peripheral components.

The AD7765 also offers a low power mode, significantly reducing power dissipation without reducing the output data rate or available input bandwidth.

The differential input is sampled at up to 40 MSPS by an analog modulator. The modulator output is processed by a series of low-pass filters. The external clock frequency applied to the AD7765 determines the sample rate, filter corner frequencies, and output word rate.

The AD7765 device boasts a full band on-board FIR filter. The full stop-band attenuation of the filter is achieved at the Nyquist frequency. This feature offers increased protection from signals that lie above the Nyquist frequency being aliased back into the input signal bandwidth.

The reference voltage supplied to the AD7765 determines the input range. With a 4.096 V reference, the analog input range is ±3.2768 V differential, biased around a common mode of 2.048 V. This common-mode biasing is achieved using the on-chip differential amplifier, further reducing the external signal conditioning requirements.

The AD7765 is available in a 28-lead TSSOP package and is specified over the industrial temperature range of −40°C to +85°C.

APPLICATIONS

* Data acquisition systems

* Vibration analysis

* Instrumentation

* High performance 24-bit Σ-Δ ADCC: wide input bandwidth with excellent dc specifications

* 115 dB dynamic range at 78.125 kHz output data rate

* 112 dB dynamic range at 156 kHz output data rate

* 156 kHz maximum fully filtered output word rate

* Pin-selectable oversampling rates of 128× and 256×

* Low power mode without reducing available input bandwidth

* Flexible serial peripheral interface (SPI)

* Fully differential modulator input