ASM1480 PCIe 3.0 Signal Switch: A Comprehensive Guide

The ASMedia ASM1480 is a widely used PCIe 3.0 differential signal multiplexer/demultiplexer switch, typically deployed in consumer and enterprise computing platforms to switch high-speed PCI Express lanes between devices such as GPUs, M.2 NVMe SSDs, or chipset uplinks. 

Overview

Features

l Quick switch for high speed, high bandwidth differential protocols

l 8 channel, 2:1 Mux/DeMux Switch with single enable

l Package: 42 pins TQFN

l Lead free, RoHs compliance.

l VCC operation: +3.3V

Functional Description

The ASM1480 provides 8-channel lane switching, typically implemented as:

· 2:1 bi-directional switch for differential pairs (TX+/TX-, RX+/RX-).

· Allows PCIe routing reconfiguration—e.g., switching CPU PCIe lanes between a discrete GPU and an M.2 SSD.

· Controlled by SEL (select) input signal, switching between Source A or Source B.

Diagram: Simplified Functional Block

             SEL = 0         SEL = 1

Host PCIe ←─────────→ Device A

          ↘         ↙

           → Device B

Pinout and Signal Description

While the full pinout is in the datasheet, here are essential signals:

Each differential signal is routed through high-speed analog switches, preserving signal integrity across PCIe 3.0 bandwidth. 

Electrical Characteristics

Applications

· Motherboard PCIe bifurcation (x16 ↔ x8/x8, or x8/x4/x4)

· M.2 SSD switching between CPU lanes and chipset

· Notebook platform with hybrid GPU/SSD lane sharing

· Server board PCIe expansion with switchable resources

· Thunderbolt/USB4-PCIe bridging applications

Practical Implementation Notes

· Controlled via a GPIO or embedded controller logic (firmware sets the SEL state).

· Route differential pairs with matched length and impedance (85 Ω differential).

· Avoid long trace stubs or vias that degrade signal integrity.

· Used passively—no retiming or buffering; signal integrity depends on PCB design.

Alternatives / Equivalents

While the ASM1480 is the most common for 8.0 GT/s applications, alternatives include:

Frequently Asked Questions (FAQ)

Is ASM1480 compatible with PCIe 4.0 or 5.0?

Not reliably. ASM1480 is rated up to PCIe Gen3 (8.0 GT/s). Using it in Gen4 (16.0 GT/s) or Gen5 (32.0 GT/s) systems will lead to significant signal degradation.

How is ASM1480 controlled?

Via a SEL logic pin (high or low), typically driven by an EC, BIOS logic, or a GPIO from the chipset/SoC.

Does the ASM1480 introduce latency?

No active logic exists inside—it behaves as a passive switch, so signal delay is minimal (a few picoseconds).

Can it be used for non-PCIe differential signals?

Yes—it's designed for high-speed differential signals, so it may be used for USB 3.x, SATA, or DisplayPort in some board designs (if within bandwidth and voltage spec).

Datasheet and Resources

· ASMedia Product Page: ASM1480

· Datasheet: Available here - ASMedia ASM1480 Datasheet.

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