**AD8047AR: A Comprehensive Guide to High-Speed Voltage Feedback Amplifiers**

The AD8047AR from Analog Devices stands as a quintessential component in the realm of high-speed analog design. As a member of the high-performance voltage feedback amplifier (VFA) family, it is engineered to deliver exceptional speed, low distortion, and wide bandwidth, making it an ideal choice for demanding applications in video, imaging, communications, and high-speed signal processing.

**Architecture and Key Specifications**

At its core, the AD8047AR leverages a classic voltage feedback architecture, which offers designers familiar and flexible gain-setting capabilities using external resistors. This architecture is particularly advantageous in applications requiring non-inverting gains greater than one, where it often outperforms current-feedback (CFB) amplifiers in terms of DC performance and output drive capability.

The amplifier is distinguished by its impressive combination of specifications:

* **High Speed:** It features a **-3 dB bandwidth of 250 MHz (G = +1)** and a very fast **slew rate of 1000 V/µs**, enabling it to cleanly amplify rapidly changing signals without introducing significant phase lag or distortion.

* **Low Distortion:** With **low harmonic distortion** figures (e.g., -80 dBc SFDR at 5 MHz), the AD8047AR is exceptional for driving high-resolution ADCs or processing signals in sensitive receiver paths where signal integrity is paramount.

* **Low Power Consumption:** Despite its high speed, it operates on a modest supply current of 5.5 mA per amplifier, a critical feature for power-sensitive portable equipment.

* **Excellent Video Performance:** It boasts **differential gain and phase errors of just 0.02% and 0.05°**, respectively, meeting the stringent requirements of professional video equipment.

**Application Circuits and Design Considerations**

The versatility of the AD8047AR allows it to be configured in numerous circuit topologies. Key applications include:

1. **Active Filters:** Its wide bandwidth makes it suitable for implementing high-speed, wideband active filters like Sallen-Key or multiple feedback (MFB) topologies.

2. **ADC Drivers:** The combination of high slew rate and low distortion makes it an excellent driver for successive approximation register (SAR) and pipeline ADCs, ensuring the analog signal is settled with high fidelity before conversion.

3. **Video Distribution Amplifiers:** Its excellent differential gain/phase performance allows it to buffer and split standard definition (SD) and high definition (HD) video signals without degrading picture quality.

4. **Transimpedance Amplifiers (TIAs):** While current-feedback amplifiers are common here, the AD8047AR can be effectively used in lower-gain photodiode amplification circuits due to its high speed and low noise.

When designing with the AD8047AR, careful attention must be paid to PCB layout and decoupling to achieve its rated performance. **Proper power supply decoupling** with ceramic capacitors placed close to the supply pins is essential to minimize parasitic inductance and prevent instability. Furthermore, maintaining a **low-impedance ground plane** and minimizing stray capacitance at the inverting input are crucial for optimizing bandwidth and stability.

**Conclusion and Comparison**

The AD8047AR occupies a unique position, offering a blend of CFB-like speed with the traditional benefits of a VFA. It provides a more predictable and stable behavior over a wide range of gains compared to CFB amps, while significantly outperforming older VFA designs like the AD847. It is an optimal solution when the design calls for high speed, low power, and superior linearity in a familiar operational amplifier configuration.

**ICGOODFIND:** The **AD8047AR is a high-performance, low-power voltage feedback amplifier** that delivers an exceptional balance of **250 MHz bandwidth, 1000 V/µs slew rate, and excellent video specifications**, making it a versatile and robust choice for high-speed analog design challenges.

**Keywords:** High-Speed Amplifier, Voltage Feedback, Low Distortion, ADC Driver, Video Performance