OPA656 is a broadband, unity gain stable, field-effect transistor input operational amplifier 8

Drive capacitor load

Capacitive load is one of the most demanding but common load conditions for operational amplifiers. Usually, the capacitive load is the input of the ADC, including additional external capacitors that can be suggested to improve the linearity of the ADC. High speed high open-loop gain amplifiers, such as OPA656, are easily affected by stability degradation and peak closed-loop response when the capacitive load is directly placed on the output pin. When considering the open-loop output resistance of an amplifier, this capacitive load introduces an additional pole in the signal path, thereby reducing the phase margin. Some external solutions have been proposed for this issue. diode The simplest and most effective solution when considering frequency response flatness, pulse response fidelity, and/or distortion is to insert a series isolation resistor between the amplifier output and the capacitive load to isolate the capacitive load from the feedback loop. This does not eliminate the poles in the loop response, but shifts them and adds zeros at higher frequencies. Adding zero eliminates the phase lag of the capacitor load pole, thereby improving the phase margin and enhancing stability.diode

The typical characteristics show the recommended RS and capacitive load, as well as the resulting load frequency response. In this case, the design objective of maximum flat frequency response was used. If certain peaks can be tolerated, lower RS values can be used. In addition, when operating at higher gains (compared to+2 used in typical characteristics), lower RS values are required for the minimum peak frequency response. Parasitic capacitance load greater than 2pF can begin to decrease the performance of OPA656. Long PC board tracking, mismatched cables, and multiple device connections can easily lead to exceeding this value. Always carefully consider this effect and try to add recommended series resistors to the OPA656 output pin as much as possible (see board layout section).diode

distortion performance

OPA656 is capable of transmitting low distortion signals in a high-frequency manner over a wide gain range. The distortion map of typical features displays typical distortions under various conditions.diode