OPA4134: PSR

Hi yoshida-san,

yoshida.mikihito said:

I use ±5V for the power supply voltage and 0.1uF bypass capacitors for the ±power supply pins. If the power supply voltage applied to the OPA4134 periodically fluctuates by about 10mV, the output of the operational amplifier will also fluctuate by about 10mV synchronously. (Voltage follower circuit, input is about 2V)

Could you show us the schematic where the op amp circuitry is not working properly?

Based on your description, it is likely that the ±5Vdc dual supply rails are generated from switching power supply. So the following recommendation is based on the switching power sources in ±5Vdc. In addition, I'd like to know the switching frequency of the power sources. 

Here are some recommendation. Once I have more information, I may be able to improve the noise attenuation further. 

1. Use 10mΩ or lower ESR ceramic capacitor (MLCC type) as bypass capacitors for each of the supply rail. Use 1uF to 22uF and low ESR MLCC capacitor to bypass noises from the ±5Vdc. Low ESR 10uF or 22uF pass pass capacitor probably will work better for the audio application. Please place these bypass capacitors next to the supply pins of the op amp.  

2. Based on figure 11, the -5V output signal should have lower voltage fluctuations than the positive +5Vdc rail. Please confirm. If this is the case, we may be able to apply LPF filters to attenuate the ripple voltage from +5V rails. 

3. What are the design requirements on the ripple voltages at the output for the audio application?

Please implement step 1 first in your op amp circuit, and tell me what is ripple noise amplitude after the implementation. In addition, please let me know the rest of questions per your application.

Best,

Raymond