**The AD7547JP: A Comprehensive Technical Overview of the 12-Bit Multiplying CMOS DAC**
In the realm of precision digital-to-analog conversion, the **AD7547JP from Analog Devices** stands as a significant and enduring component. This 12-bit multiplying CMOS DAC has established itself as a reliable solution for a wide array of applications, from industrial process control to sophisticated audio equipment. Its architecture combines the benefits of **low power consumption**, inherent to CMOS technology, with the precision and flexibility required for complex analog signal generation.
At its core, the AD7547JP is a **monolithic, 12-bit, current-output digital-to-analog converter**. The term "multiplying" is a key differentiator; it signifies that the device's reference input is designed to accept AC signals, not just a fixed DC voltage. This allows the DAC to function not only as a simple converter but also as a **programmable attenuator or a digital modulator**. The output current is a product of the digital input code and the analog reference voltage, enabling operations like waveform generation and complex gain control that are impossible with a non-multiplying DAC.
The device is constructed around a precision laser-trimmed thin-film R-2R ladder network, which is responsible for its **high accuracy and linearity**. The internal circuitry includes input latches, providing a double-buffered interface. This means it features a 12-bit input register that can be loaded from a 12-bit bus, followed by a DAC register that holds the digital code currently being converted. This double-buffering is crucial for applications requiring simultaneous update of multiple DACs, as it prevents spurious analog outputs during the data loading process.
A key feature of the AD7547JP is its **compatibility with a wide range of microprocessors**. Its interface logic is designed for straightforward connection to 4-bit, 8-bit, 12-bit, or 16-bit data buses, minimizing the need for external glue logic. The separate "Load DAC" control signal allows the user to write data to the input register without affecting the analog output. The output is only updated when this dedicated signal is pulsed, ensuring clean and glitch-free transitions.
The analog performance of the AD7547JP is characterized by its **excellent multiplying characteristics**. It offers a high feedthrough rejection, meaning when the DAC is loaded with a code of zero, the AC signal on the reference input is effectively blocked from appearing at the output. Its four-quadrant multiplication capability allows both the reference voltage and the digital code to be bipolar, further expanding its utility in designing circuits that require handling signals with positive and negative polarities.
In a typical application circuit, the current output (IOUT) of the AD7547JP is converted into a voltage using an external operational amplifier configured as a current-to-voltage converter. The choice of this op-amp and the feedback resistor is critical for achieving the desired **settling time, offset, and noise performance**. The device's design provides the flexibility to choose these external components to optimize for speed or precision as needed by the specific application.
**ICGOOODFIND**: The AD7547JP remains a quintessential example of a versatile and robust digital-to-analog converter. Its unique combination of multiplying capability, microprocessor compatibility, and precision CMOS architecture has cemented its place as a fundamental building block for design engineers seeking reliable performance in digitally-controlled analog systems.
**Keywords**: Multiplying DAC, CMOS, 12-Bit Resolution, Programmable Attenuator, Microprocessor Compatible.
