CMOS, 16-Bit, 195 kSPS Sigma-Delta ADC
The analog input is continuously sampled by an analog modulator eliminating the need for external sample-and-hold circuitry. The modulator output is processed by two Finite Impulse Response (FIR) digital filters in series. The on-chip filtering reduces the external antialias requirements to first order, in most cases. The group delay for the filter is 215.5 µs, while the settling time for a step input is 431 µs. The sample rate, filter corner frequency, and output word rate are set by an external clock that is nominally 12.5 MHz.
Use of a single bit DAC in the modulator guarantees excellent linearity and dc accuracy. Endpoint accuracy is ensured by on-chip calibration. This calibration procedure minimizes the zero-scale and full-scale errors.
Conversion data is provided at the output register through a flexible serial port or a parallel port. This offers 3-wire, high speed interfacing to digital signal processors. The serial interface operates in an internal clocking (master) mode, whereby an internal serial data clock and framing pulse are device outputs. Additionally, two AD7722s can be configured with the serial data outputs connected together. Each converter alternately transmits its conversion data on a shared serial data line.
The part provides an accurate on-chip 2.5 V reference. A reference input/output function is provided to allow either the internal reference or an external system reference to be used as the reference source for the part.
The AD7722 is available in a 44-pin PQFP package and is specified over the industrial temperature range from –40°C to +85°C.
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
The EVAL-AD7722CBZ is a fully featured evaluation kit for the AD7722. This board operates in stand alone mode or in conjunction with the Evaluation Controller board. When operated with the Evaluation Controller board, software is provided enabling the user to perform detailed analysis of the ADC's performance. This software includes the technical note describing the operation and set up of the evaluation board in standalone operation or when operated with the Evaluation Controller board.
Ask the Applications Engineer-27: What problems am I most likely to run into...
(Analog Dialogue, Vol. 33, No. 2, February, 1999)
MS-2210: Designing Power Supplies for High Speed ADC
Delta-Sigma Rocks RF, As ADC Designers Jump On Jitter
(Electronic Design, 1/12/06)
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.
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