# Separate drawn diagrams in a schematic

In below circuit I pointed(red arrow) the part with "power supply rails with two caps".

As you see, it is drawn seperately from the main circuit.

1-) Does that mean the capacitors C1 and C2 are optional?

2-) I'm having some days spikes from the circuit output(ADC). I was planning to investigate the power supply. Below is the sampled data from a noisy day. Is there a possiblity that this can be power supply noise?:

edit:

Here AC coupled scope view of 15V to gnd rail:

Here in freq. domain:

• It's not optional. The 2 capacitors are drawn in between power rails (+15, GND and -15) and that means you have to connect the capacitors that way. And the purpose of those is to reduce the supply noise. Nov 23, 2016 at 11:22
• And before you ask why is it drawn that way - It's because the capacitors aren't part of the amplifier circuit, they are part of the power supply. By putting them separate it avoids cluttering the the signal path part of the schematic with unrelated parts. Nov 23, 2016 at 11:26
• A single question per post would get you clearer answers and would help future researchers. Nov 23, 2016 at 13:13

1-) Does that mean the capacitors C1 and C2 are optional?

no!

I really don't like the schematic for several reasons (e.g. with a slight reorganization, U3 wouldn't have the ground "above", other cosmetic reasons), but the fact that they chose to dangle the 100nF stabilizing capacitors just "anywhere" on the board really makes it a bad schematic, in my humble opinion.

I was wondering where the designer of the circuit intended them to be.

I came to the conclusion that they were probably meant to be as close as possible to the lower side of R4, essentially forming a low-pass filter with the "zero adjust" voltage divider. Strange choice, by the way, to introduce yet another name for this ground net, and call it -OUT.

I personally dislike this style of drawing capacitors just "somewhere in the schematic, so we don't forget to include them in the list of components to buy". The placement of such capacitors is critical to their function and performance (long trace = high inductance = less effective to swallow noise)

2-) I'm having some days spikes from the circuit output(ADC). I was planning to investigate the power supply. Below is the sampled data from a noisy day. Is there a possiblity that this can be power supply noise?

Yes.

But it's impossible to say, because you seem to be sampling at a very low rate (looks like < 1kS/s), and there's nothing indicating you limit the bandwidth. So this might just be some proper signal aliasing. Or Megahertzes of noise power density concentrating in your Nyquist band. When using an ADC, you must always make sure you apply the Nyquist sampling theorem and limit your signal bandwidth with an analog anti-aliasing filter!