One important characteristic of the OPAx892 amplifier is the decompensated architecture. By pushing out the dominate pole to a higher frequency using this common technique, the amplifier is no longer stable in lower gain configurations. The minimum stable gain for the OPAx892 is specified to be 10 V/V. When a lower gain is needed in a preamp or buffer application, a related product to be considered is the OPA891. Because the OPA891 is not decompensated, the gain-bandwidth product is approximately an order of magnitude lower than the OPAx892. Both of these amplifiers have similar noise performance, but the best bandwidth and distortion performance comes from using the correct amplifier depending on the gain needs of the application.

When applications require gain of 10 V/V or larger, choose the OPAx892 to obtain a low value of harmonic distortion and THD+N. Figure 7-3 shows a where in the analog signal chain this type of amplification can be required. Often found in applications such as ultrasound, audio, and sonar, a preamp is used near the input sensor to boost the signal to a more practical level with an emphasis on keeping noise and distortion as small as possible. Later in the signal chain, significantly more gain can be required to provide for other required functions such analog filtering, mixing, splitting, or just the need to match the signal level to a following device. An amplifier such as the OPAx892 maintains the fidelity of the signal by providing the needed gain with significantly impacting distortion over a wide bandwidth and output swing. Figure 7-4 shows the amplifier design example. The amplification stage provides an additional 10 V/V of gain to the analog signal chain.

Figure 7-3 Gain Stage in an Analog-Front-End Block Diagram

Figure 7-4 Noninverting Gain Configuration