OP amp usage Features

1. do not connect the capacitor directly in the op amp output

In the DC signal amplification circuit, sometimes in order to reduce the noise, directly in the OP amp output and connect to the capacitor. Although the DC signal is amplified, it is not safe to do so. When there is a step signal input or power-on instantaneous, the OP amp output current will be relatively large, and the capacitance will change the phase characteristics of the loop, causing the circuit self-oscillation, which we do not want to see. The correct way to make the capacitor should be composed of RC circuit, is the output of the OP amp first string into a resistor, and then then to engage in the capacitor . This can greatly reduce the OP amp output instantaneous current, and will not affect the loop phase characteristics, can avoid oscillation.

2, do not amplify the circuit feedback circuit and connect the capacitance

Also is a DC signal amplification circuit, in order to decouple, accidentally put the capacitor and received a feedback loop, the feedback signal phase has changed, it is easy to oscillate. Therefore, in the amplification circuit, the feedback loop can not be added to any circuit affecting the signal phase. This extends to a regulated power supply circuit, such as, and the C3 of the feedback foot is wrong. In order to reduce the ripple, C3 and RL can be connected in parallel to increase the negative feedback action of the ripple and suppress the output ripple.

3. Notice the swing of the op amp

Any op amp can not be the ideal op amp, output voltage can not reach the power supply voltage, generally based on MOS op amp is rail-to-rail op amp, in the case of no-load output to reach the supply voltage, but the output will be with a certain load, the larger the load, the more output landing. Transistor-based op amp output amplitude relative small, some op amp output amplitude than the supply voltage to small 2~6v, such as NE5532 figure is TL TLC2272 in the output characteristics of the power supply, it belongs to rail-to-rail op amp, if the device as the ADC sampling of the pre-level amplification (such as), Single power supply, the input and output become non-linear when the input is close to 0V. The solution is to introduce a negative power supply, such as a negative power supply that joins the -1V at 4 feet, so that the output and input are linear over the entire input range.

4. Note the layout of the feedback loop

Feedback loop components must be close to the OP amp, and the body CB line to be as short as possible, while avoiding digital signals, crystal oscillator and other sources of interference. The layout of the feedback loop is unreasonable, it will be easy to introduce noise, which will lead to self-excited oscillation.

5, should pay attention to the power filter

OP amp Power Filter should not be ignored, the quality of power directly affect the output. Especially for high-speed op amp, the Power ripple on the op amp output interference is very large, the bad will become self-excited oscillation. So the best op-amp filter is to add a 0.1uF decoupling capacitor and a dozens of UF tantalum capacitor to the op amp's power foot, or a small inductor or bead to make the effect better.

OP amp usage Features