24-Bit, 156 kSPS,112dB

Σ∆ ADC,

With On-Chip Buffers, Serial Interface

Preliminary Technical Data

AD7765

Rev. PrC

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FEATURES

High performance 24-bit Sigma-Delta ADC

112dB SNR at 78kHz output data rate

109dB SNR at 156 kHz output data rate

156 kHz maximum fully filtered output word rate

Pin-selectable over-sampling rate (128x & 256x)

Flexible SPI serial interface

Fully differential modulator input

On-chip differential amplifier for signal buffering

On-chip Reference Buffer

Low pass FIR filter

Over-range alert pin

Digital gain correction registers

Power down mode

Synchronization of multiple devices via SYNC pin

Daisy Chaining

APPLICATIONS

Data acquisition systems

Vibration analysis

Instrumentation

PRODUCT OVERVIEW

The AD7765 high performance, 24-bit, sigma delta analog to

digital converter combines wide input bandwidth, high speed

and performance of 112dB at a 156Khz output data rate with

the benefits of sigma delta conversion, while, also offering

excellent DC specifications which make the converter ideal for

high speed data acquisition of AC signals where DC data is also

a requirement.

A wide dynamic range combined with significantly reduced

anti-aliasing requirements simplifies the design process. The

AD7765 offers pin-selectable decimation rates of 128x

and 256x. Other features include an integrated buffer to drive

the reference, a differential amplifier for signal buffering and

level shifting.

The addition of an internal gain register, an over-range alert

pin, and a low-pass digital FIR filter make the AD7765 a

compact highly integrated data acquisition device requiring

minimal peripheral component selection. The AD7765 is

ideally suited to applications demanding high SNR without

necessitating design of complex front end signal processing.

FUNCTIONAL BLOCK DIAGRAM

Multi-Bit

Sigma-Delta

Modulator

Reconstruction

Decimation

FIR Filter

Engine

DIFF

+

_

BUF

Interface Logic

and

Offset & Gain Correction

Registers

MCLK

SYNC

RESET/PWRDN

VIN-

VIN+

AD7765

VREF+

REFGND

AVDD1

AVDD2

AVDD3

DECAP

RBIAS

DVDD

OVERRANGE

AVDD4

VINA-

VINA+

VOUTA- VOUTA+

Figure 1.

The differential input is sampled at up to 40MS/s by an analog

modulator. The modulator output is processed by a series of

low-pass filters. The sample rate, filter corner frequencies and

output word rate are determined by the external clock

frequency supplied to the AD7765.

The reference voltage supplied to the AD7765 determines the

analog input range. With a 4V reference, the analog input range

is ±3.2V differential biased around a common mode of 2V. This

common mode biasing can be achieved using the on-chip

differential amplifiers, 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 from -40°C to

+85°C

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