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page_id: wsd-do-we-need-ocd-io-pads-for-digital-3v3-design-ef2eee0e
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title: "Thread: Do we need OCD IO pads for digital 3v3 design"
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route: /evidence/i-information/questions/threads/do-we-need-ocd-io-pads-for-digital-3v3-design
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summary: 10 Discord messages from ℹ️ - Information/⁉️-questions/threads/do-we-need-ocd-io-pads-for-digital-3v3-design.md.
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last_updated: 2026-08-19
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talk_route: /evidence/i-information/questions/threads/do-we-need-ocd-io-pads-for-digital-3v3-design/talk
---

# Thread: Do we need OCD IO pads for digital 3v3 design

Category: **ℹ️ - Information**
Parent channel: **#⁉️-questions**
Thread ID: `1513432126190522469`

Messages: **10**

## message-1513432126190522469

**2026-06-08T06:38:57.093+00:00 — Jason Yang (@.pogeg)**

- Message ID: `1513432126190522469`
- Author ID: `236632873782738944`
- Nickname: Jason Yang
- User name: .pogeg
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1513432126190522469/1513432126190522469
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/do-we-need-ocd-io-pads-for-digital-3v3-design/2026-06/2026-06.json

**Content**

```text
For our design, we're planning on using a pure 3v3 digital design (no analog, 3v3 SCL and SRAM). In that case, is switching from foundry provided IO pads to OCD pads necessary?
```

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## message-1513434109140140182

**2026-06-08T06:46:49.865+00:00 — Leo Moser (mole99) (@mole99)**

- Message ID: `1513434109140140182`
- Author ID: `323371864074485771`
- Nickname: Leo Moser (mole99)
- User name: mole99
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1513432126190522469/1513434109140140182
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/do-we-need-ocd-io-pads-for-digital-3v3-design/2026-06/2026-06.json

**Content**

```text
No, it is not necessary. In this case, you can keep using the foundry pad cells.

The OCD cells add levelshifters between IO and core, which allows you to have IO voltage > core voltage. For example, you could have a 3.3V core voltage and a 5V IO voltage.

If you run everything at 3.3V, then you can simply use the FD cells.

Currently, there are no IO cells with 3.3V transistors (normal gate oxide). Both the FD and OCD cells use 5V transistors (thick gate oxide).
```

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## message-1513434177914146906

**2026-06-08T06:47:06.262+00:00 — Leo Moser (mole99) (@mole99)**

- Message ID: `1513434177914146906`
- Author ID: `323371864074485771`
- Nickname: Leo Moser (mole99)
- User name: mole99
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1513432126190522469/1513434177914146906
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/do-we-need-ocd-io-pads-for-digital-3v3-design/2026-06/2026-06.json

**Content**

```text
As you probably know, the 3.3V SCL and SRAM are yet to be silicon verified.
```

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## message-1513444673346342982

**2026-06-08T07:28:48.568+00:00 — tnt (@246tnt)**

- Message ID: `1513444673346342982`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1513432126190522469/1513444673346342982
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/do-we-need-ocd-io-pads-for-digital-3v3-design/2026-06/2026-06.json

**Content**

```text
Also to note the foundry cells although designed for 5V provide more than acceptable performance running at 3.3V. ( > 100 MHz without issues ).
```

**Reactions**

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## message-1522993158810636470

**2026-07-04T15:51:04.905+00:00 — Tim Edwards (@rtimothyedwards_19428)**

- Message ID: `1522993158810636470`
- Author ID: `1365118310701600900`
- Nickname: Tim Edwards
- User name: rtimothyedwards_19428
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1513432126190522469/1522993158810636470
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/do-we-need-ocd-io-pads-for-digital-3v3-design/2026-07/2026-07.json

**Content**

```text
Sounds like there might be some interest in a pure 3.3V I/O library to try to hit higher performance?  It's a bit trickier than my hack method of downsizing the 5V SRAMs to 3.3V (although that worked surprisingly well) because a lot of the I/O pad device sizing is based on ESD targets.  And it cannot just be "silicon verified" by doing a functional test---it needs to be zap-tested.  The dual voltage I/O library does not need zap testing because nothing touching the pad itself has been modified, only internal core-facing circuits.  Its ESD characteristics should be exactly like the original 5V I/O library.
```

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## message-1523001736501919884

**2026-07-04T16:25:09.986+00:00 — tnt (@246tnt)**

- Message ID: `1523001736501919884`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1513432126190522469/1523001736501919884
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/do-we-need-ocd-io-pads-for-digital-3v3-design/2026-07/2026-07.json

**Content**

```text
I mean inputs of the dual one reached 188 MHz (and probably limit is tt infra and not pad) and outputs would be fine above 100 M given measured rise/fall time.
```

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## message-1523005910845362286

**2026-07-04T16:41:45.227+00:00 — Leo Moser (mole99) (@mole99)**

- Message ID: `1523005910845362286`
- Author ID: `323371864074485771`
- Nickname: Leo Moser (mole99)
- User name: mole99
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1513432126190522469/1523005910845362286
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/do-we-need-ocd-io-pads-for-digital-3v3-design/2026-07/2026-07.json

**Content**

```text
But outside of TT, people might still be interested. (I definitely am 😁)
```

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## message-1523006175275122689

**2026-07-04T16:42:48.272+00:00 — BreakingTaps (@polyfractal)**

- Message ID: `1523006175275122689`
- Author ID: `384390069412429834`
- Nickname: BreakingTaps
- User name: polyfractal
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1513432126190522469/1523006175275122689
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/do-we-need-ocd-io-pads-for-digital-3v3-design/2026-07/2026-07.json

**Content**

```text
is there a disadvantage to using the OCD cells if everything is 3v3? Worse timing or power or something? I didn't realize you could use the FDs
```

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## message-1523014445142511873

**2026-07-04T17:15:39.962+00:00 — RebelMike (@rebelmike)**

- Message ID: `1523014445142511873`
- Author ID: `691780627338625077`
- Nickname: RebelMike
- User name: rebelmike
- Type: `Default`
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Hmm, I could see it either way - splitting the power domains maybe reduces noise, joining them maybe increases stability through more pins?  Not sure which is preferable.
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## message-1523032263225380965

**2026-07-04T18:26:28.124+00:00 — tnt (@246tnt)**

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- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/do-we-need-ocd-io-pads-for-digital-3v3-design/2026-07/2026-07.json

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**Content**

```text
I meant that more than likely the IO themselves already go way above what we measured in TT and getting non trivial logic in gf180 meeting 200 MHz is quite the challenge, so it's not like the IO are a giant limiting factor ATM.
```

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