## AD679: High-Performance 14-Bit Sampling ADC The **AD679** is a precision 14-bit Analog-to-Digital Converter (ADC) manufactured by Analog Devices. It is designed for high-speed data acquisition and features a complete sampling architecture, meaning it includes an on-chip sample-and-hold (SHA) and a voltage reference. --- ### 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Resolution** | 14 Bits | | **Throughput Rate** | 128 kSPS (Kilo Samples Per Second) | | **Conversion Time** | 7.8 µs (max) | | **Input Voltage Range** | ±5V, ±10V, or 0V to 10V (Selectable) | | **Power Consumption** | 400 mW (typical) | | **Package Options** | 28-pin DIP, 28-pin SOIC, 44-pin JLCC | --- ### 2. Functional Components The internal architecture of the AD679 consists of several critical electronic sections that allow it to process analog signals into digital data with high accuracy: * **Sample-and-Hold Amplifier (SHA):** Captures the input signal and holds it steady during the conversion process. This is essential for converting high-frequency AC signals. * **Successive Approximation Register (SAR):** The core "logic" of the conversion. It compares the input voltage against a series of binary weights to determine the digital value. * **Internal Reference:** Features a buried Zener reference providing a stable 10V output. This can be used internally or buffered for external circuits. * **Clock Circuit:** It includes an internal clock, but it can also be driven by an external clock source for synchronization. * **Digital Interface:** Provides 14-bit parallel data output. It uses standard microprocessor control signals like `CS` (Chip Select), `RD` (Read), and `CE` (Chip Enable). --- ### 3. Pin Configuration Overview The AD679 uses a 28-pin layout. Key pins include: * **V_IN:** Analog input signal. * **REF OUT/REF IN:** 10V reference output or input for external reference. * **BIP OFF:** Bipolar offset adjustment. * **D13 - D0:** Digital output bits (D13 is MSB, D0 is LSB). * **STS (Status):** Goes high during conversion and low when data is ready. * **AGND/DGND:** Separate Analog and Digital grounds to minimize noise interference. --- ### 4. Typical Applications Due to its 14-bit resolution and integrated SHA, the AD679 is commonly used in: 1. **Digital Signal Processing (DSP):** High-speed front ends for processors. 2. **Medical Instrumentation:** Precision imaging and diagnostic equipment. 3. **Industrial Controls:** High-accuracy sensor monitoring and robotics. 4. **Data Acquisition Systems:** Multi-channel systems requiring reliable throughput. --- ### 5. Interfacing Example (Pseudo-Logic) To initiate a conversion and read the data, a typical microcontroller follows this sequence: ```c // Pseudo-code for AD679 data retrieval void read_AD679() { trigger_start_conversion(); // Pulse the Convert Start line while(STATUS_PIN == HIGH); // Wait for conversion to complete enable_output(); // Set CS and RD low data = read_parallel_bus(); // Read the 14-bit data from D13-D0 disable_output(); // Reset CS and RD high } ``` ---