C-PHY Receiver Input Buffer With Common-Mode EMI Injection

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Solution Overview

Problem

Mobile communication devices face challenges in rejecting electromagnetic interference (EMI) in high-speed C-PHY interfaces, particularly due to increasing clock rates and proximity to RF transceivers, which affect common mode noise rejection in receivers.

Innovation Solution

Implementing an input buffer with a pair of input transistors and injection circuits, each coupled to a multi-wire serial bus, using resistors and capacitors to inject common mode noise into the sources of the transistors, thereby stabilizing the common mode voltage and enhancing noise rejection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the clock rate is increased to meet higher data rate demands, then productivity is improved, but the device becomes more susceptible to electromagnetic interference

Engineering Contradiction:

Improvedata rateVSAvoidelectromagnetic interference susceptibility

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by injecting a common-mode signal that is the inverse of expected interference patterns before the actual interference occurs. The injection circuit generates a preemptive counter-signal that cancels out upcoming electromagnetic interference from RF transceivers, allowing high-speed data transmission without the adverse effects of EMI.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent converts the harmful electromagnetic interference into a beneficial effect by using the same RF sources that cause interference to generate a compensating common-mode signal. The injection circuit captures the interference pattern and transforms it into a useful counter-signal that, when injected into the differential pair, actually cancels the harmful interference and improves signal integrity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Speed

If transmission clock frequency is increased, then data rate is improved, but common mode noise rejection deteriorates

Engineering Contradiction:

Improvetransmission clock frequencyVSAvoidcommon mode noise rejection

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The injection circuit performs preliminary action by pre-loading the differential pair with a common-mode signal that establishes a stable reference level before data transmission begins. This preliminary signaling conditions the receiver to reject common-mode noise that will occur at higher clock frequencies, maintaining noise rejection performance despite increased transmission speed.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the electrical parameters of the reception circuit by dynamically adjusting the common-mode voltage level through the injection circuit. By modifying the common-mode voltage parameter in response to detected interference conditions, the system maintains optimal noise rejection characteristics across varying clock frequencies and interference environments.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If RF transceivers are placed in close proximity to improve device integration, then device complexity is reduced, but electromagnetic interference increases

Engineering Contradiction:

Improvedevice integrationVSAvoidelectromagnetic interference

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The injection circuit acts as an intermediary between the RF transceiver and the high-speed serial interface. It captures the electromagnetic interference generated by the RF transceiver and transforms it into a useful common-mode signal that, when injected into the differential pair, cancels the harmful interference. This mediator approach allows close proximity placement of RF and data components without mutual interference.

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution effectively cancels high-amplitude common mode noise, improving the reliability and performance of C-PHY receivers by stabilizing the output common mode voltage and minimizing signal distortion.

Implementation Method 1

A first injection circuit includes three or more resistors configured to couple the wires of the multi-wire serial bus to a common node of the first injection circuit. The first injection circuit also includes a capacitor configured to couple the common node of the first injection circuit to the source of the first input transistor.

Methodology Applied

Scientific EffectCommon mode noise injection:

Data Source

PatentUS12353350B2Radio frequency interference common mode injection in a C-PHY receiver

Publication Date: 2025.07.08 QUALCOMM INC

AI summary

An input buffer includes a pair of input transistors and associated injection circuits. A first input transistor has a source coupled to a first voltage rail through a first current source and a gate coupled to a first wire of a multi-wire serial bus. Three or more resistors in a first injection circuit couple the wires of the serial bus to a first common node, which is coupled to the source of the first input transistor by a first capacitor. A second input transistor has a source coupled to the first voltage rail through a second current source and a gate coupled to a second wire of the serial bus. Three or more resistors in a second injection circuit couple the wires of the multi-wire serial bus to a second common node, which is coupled to the source of the second input transistor by a second capacitor.