The AD7725 is a complete 16-bit, sigma-delta analog to digital converter with on-chip user-programmable signal conditioning. The output of the modulator is processed by three cascaded finite impulse response (FIR) filters, followed by a user-programmable post processor. The user has complete control over the filter response, the filter coefficients, and the decimation ratio. Up to 108 coefficients can be held in the post processor.
Sixteen-bit performance is obtained for input bandwidths up to 300kHz and an output word rate of 600kHz maximum. A crystal oscillator or an external clock sets the input sample rate and has a specified value of 9.6MHz and a maximum value of 14.4MHz. The CLKIN frequency directly determines the maximum input bandwidth of the device with the relationship being BW(max) = CLKIN/32. The conversion data is available via a serial or parallel interface.
Using Systolix's PulseDSP* technology, the Post Processor can be programmed using either the on-chip, default filter or a user-defined filter in the form of a configuration file. The user defined filter can be loaded into the device from a DSP or an external EPROM with a serial interface or from a DSP with a parallel interface.
The user-defined filter configuration file can be generated using a digital filter design package called 'Filter Wizard' which can be downloaded at AD7725 Development Kit. This package allows the user to design different filter types and generates the appropriate configuration file to be loaded to the device.
An accurate 2.5 V reference is available on chip for the modulator. A reference input/output function is provided to allow either the on board reference or an external system reference to be used as the reference source for the modulator.
The device is offered in a 44-pin PQFP package and is designed to operate from -40°C to +85°C.
*PulseDSP is a Trademark of Systolix