# Bypass Capacitors

This constraint guarantees that bypass and decoupling capacitors are placed close to the correct pins.

### Automatic Detection

When bypass capacitors are connected between a component and ground, they're automatically detected. 

They're assigned to a parent pin using this priority order:

1. Explicit connection by wire in the schematic
2. Parent pins with voltage-type names (e.g. `Vin`)
3. If a capacitor is connected to multiple pins of the same name, it's split equally across them.

### Recommended Patterns

For a capacitor to be assigned correctly to a parent pin, the best approach is to connect it directly to the pin in the schematic with a wire. Other patterns, such as blocks of capacitors linked by a net label or power port, will still be interpreted using our rules, but with lower priority. 

You can also manually edit the assignment in the interface.

### Constraint Details

<figure><img src="/files/LDkSycXMGI3USkbUMHB3" alt=""><figcaption></figcaption></figure>

Configure bypass capacitor constraints in the "Bypass Capacitors" section of Circuit Comprehension.&#x20;

To set a bypass capacitor constraint, fill in the following fields:

* Capacitor (reference designator)
* Component being bypassed
* Pin on that component being bypassed
* Capacitance

Quilter automatically places capacitors with smaller capacitance values closer to power pins for a low-latency, low-impedance path. It can also position a single capacitor to bypass multiple pins on the same IC.

### Physics Rule Checks

The PRCs that validate this constraint after compilation are:

**Pin Distance** calculates the Euclidian distance between the closest edges of two pins.

**Layer Switch Count** finds the number of times there is a layer switch in a trace path between two pins

**Ground Plane Overlap** determines if the ground plane below net traces overlaps at all relevant points.

**Trace Path Length** calculates the trace length between two pins of interest.

### FAQs

<details>

<summary>Can Quilter handle multiple bypass capacitors for a single IC?</summary>

Yes, Quilter can identify and optimize one-to-many relationships between ICs and their bypass capacitors, ensuring effective decoupling across different frequency ranges.

</details>

<details>

<summary>How does Quilter decide where to place bypass capacitors?</summary>

Quilter strategically places smaller capacitors near high-current voltage sinks to minimize impedance and stabilize power delivery. The algorithm reduces trace lengths and via counts to lower parasitic effects in the decoupling network.

</details>

<details>

<summary>Can I override Quilter’s automatic placements?</summary>

Yes, you can manually adjust or pre-place bypass capacitors in your input file if you have specific design requirements.

</details>


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