What is the difference between choosing the same capacitors in parallel and arranging capacitors of different sizes in a bypass filter circuit?

btty038

What is the difference between choosing the same capacitors in parallel and arranging capacitors of different sizes in a bypass filter circuit? [Copy link]

btty038

What effect does the large and small capacitors have on the circuit when filtering out high and low frequencies?

btty038

btty038

The previous picture does not describe the problem clearly. The picture above describes the problem intuitively...

maychang

There may be multiple digital circuit chips on a circuit board, such as a single-chip microcomputer and single-chip microcomputer expansion memory, I/O port expansion chip, etc. On the electrical schematic, multiple bypass capacitors with the same value are drawn together, but on the circuit board, the capacitors are not placed together, but placed next to each chip, and the two ends of the capacitor are directly connected to the power pin and ground pin of the chip (there may be a design where two or three chips share one capacitor). The purpose of this design is to use the capacitor next to it to supply power when the current consumption of the chip changes suddenly, without affecting the operation of other chips.

This can be seen most clearly by looking at a PC motherboard.

maychang

As for large capacitors and small capacitors connected in parallel on the same power supply, there is usually only one or a few large capacitors placed at the power input of the circuit board, unlike small capacitors which are almost assigned one capacitor to each chip.

This can be seen most clearly by looking at a PC motherboard.

gmchen

Except for the case where electrolytic capacitors are connected in parallel with ceramic capacitors, it is not recommended to connect several ceramic capacitors with different capacities in parallel.

Ceramic capacitors have a resonance point (capacitance and distributed inductance), and ceramic capacitors beyond the resonance point become inductive. The approach on the 4th floor is not recommended. Because in that case, ceramics of different capacities are connected in parallel, which may cause parallel resonance in the worst case, and the bypass effect on the parallel resonance frequency is very poor.

The situation on the first floor is recommended. It is OK to allocate one or several to each integrated circuit chip, because the resonance point is the same, there is no danger of resonance. And the distributed inductance after parallel connection is reduced, and the bypass effect is better. On the computer motherboard, the CPU bypass is handled in the same way.

btty038

maychang posted on 2024-1-28 11:33 As for large capacitors and small capacitors connected in parallel on the same power supply, there is usually only one or a few large capacitors placed at the power inlet of the circuit board, unlike small...

Is the board dealing with the sudden change in the chip feed port for the digital circuit processing or is there some other reason?

btty038

gmchen posted on 2024-1-28 17:42 Except for the case where electrolytic capacitors are connected in parallel with ceramic capacitors, it is not recommended to connect several ceramic capacitors with different capacities in parallel. Ceramic capacitors have a resonance point (capacitance...

There have been some differences in this view recently. My personal opinion is that the capacitor is the result of the fusion and integration of multiple feeds of the chip fed by the digital part. I am still a little confused about the central idea.