AD829:  High Speed, Low Noise Video Op Amp

The AD829 is a low noise (1.7 nV/√Hz), high speed op amp with custom compensation that provides the user with gains of 1 to 20 while maintaining a bandwidth >50 MHz. Its 0.04° differential phase and 0.02% differential gain performance at 3.58 MHz and 4.43 MHz, driving reverse-terminated 50 Ω or 75 Ω cables, makes it ideally suited for professional video applications. The AD829 achieves its 230 V/μs uncompensated slew rate and 750 MHz gain bandwidth while requiring only 5 mA of current from power supplies.

The external compensation pin of the AD829 gives it exceptional versatility. For example, compensation can be selected to optimize the bandwidth for a given load and power supply voltage. As a gain-of-2 line driver, the −3 dB bandwidth can be increased to 95 MHz at the expense of 1 dB of peaking. Its output can also be clamped at its external compensation pin. The AD829 exhibits excellent dc performance. It offers a minimum open-loop gain of 30 V/mV into loads as low as 500 Ω, a low input voltage noise of 1.7 nV/√Hz, and a low input offset voltage of 1 mV maximum. Common-mode rejection and power supply rejection ratios are both 120 dB.

This op amp is also useful in multichannel, high speed data conversion where its fast (90 ns to 0.1%) settling time is important. In such applications, the AD829 serves as an input buffer for 8-bit to 10-bit ADCs and as an output I/V converter for high speed DACs.

Operating as a traditional voltage feedback amplifier, the AD829 provides many of the advantages that a transimpedance amplifier offer. A bandwidth >50 MHz can be maintained for a range of gains through the replacement of the external compensation capacitor. The AD829 and the transimpedance amplifier are both unity-gain stable and provide similar voltage noise performance (1.7 nV/√Hz); however, the current noise of the AD829 (1.5 pA/√Hz) is less than 10% of the noise of transimpedance amplifiers. The inputs of the AD829 are symmetrical.