the OPA192 output ripple will accumulate when cascade the OPA192. is there any RC selection guide for OPA192 output?
Peter,
OPA192 is a LINEAR amplifier with no zero drift circuitry, thus there should be no voltage ripple at the output unless a switching power supply or another EXTERNAL signal feeds into its signal path. Please use the scope to trouble-shoot around the circuit (supplies, input,etc.) to determine what exactly causes the ripple.
The choice of the RC depends on the ripple frequency and what output error you may tolerate in case of resistve loading - see the small-signal overshoot vs capacitive load. However, in order to assure stability of the circuit, you must make sure that with your choice of RC, the overshoot is smaller than 25%.
Btw, also make sure to connect low-ESR, 0.1-µF or greater, ceramic bypass capacitors between each supply pin and ground.
Peter,
What you show below is not a voltage ripple but rather voltage noise with each subsequent stage amplification corresponding to its actual noise gain. You may either try to filter out the noise with RC in the feedback as shown on your schematic below or by placing a low-pass filter at the output.
The only limitation in feedback filtering is the question of what minimum bandwidth you can live with; your current RC choice of 10k and 10pF, limits the bandwidth to fc=1/(6.28*RC) =1.6MHz. If you can tolerate 160kHz bandwidth, you should increase Cf to 100pF while if you can live with 16kHz bandwidth, use Cf of 1nF, etc.
Feedback filtering is convenient but NOT the most effective way to filter out the noise because all it does is to lower the noise gain to 1 when Cf becomes a short. If you need to filter the noise further, you must add a low pass RC filter at the output (see below) where gain rolls off at constent rate of -20dB/decade and thus more effectively filters out the noise. Using 1k series resistor with 1nF cap, CL, limits the bandwidth to 160kHz but more effectively filters out the noise than the equivalent feedback filtering scheme. With RC filtering at the output, you must be careful to assure stability - 1k||1nF choice assures the stability of the circuit - see below.
To learn more about circuit stability, please see the link below:
