FDD Leakage Cancellation via Auxiliary Replica Circuit

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Solution Overview

Problem

In full division duplex (FDD) systems like WCDMA, the simultaneous operation of transmitters and receivers leads to blocker interference, which degrades receiver sensitivity through saturation, inter-modulation distortion, and second-order inter-modulation distortion, and conventional solutions like SAW filters introduce insertion loss, increased bias current, and reduced integration and cost due to off-chip components.

Innovation Solution

An auxiliary circuit is introduced to generate a blocker replica by collecting leakages from the outbound RF signal, down-converting, and up-converting them to cancel interference, using a buffer, up/down converters, a phase shifter, gain tuner, low pass filter, and DC offset canceller to adjust and filter the baseband signal, thereby subtracting the blocker interference from the inbound RF signal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If SAW filter is deployed to reject out-of-band blockers, then blocker rejection is improved, but insertion loss increases and integration level degrades

Engineering Contradiction:

Improveblocker rejectionVSAvoidintegration level

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The harmful blocker signal is extracted from the received signal by generating a separate blocker replica through the auxiliary circuit, which captures the transmitter leakage path independently and reconstructs the blocker signal to be subtracted from the received signal

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

A blocker replica is created by copying the transmitter leakage signal through the auxiliary circuit path, which includes capturing the leakage at the LNA input, down-converting it, adjusting its characteristics, and re-up-converting it to match the original blocker signal for cancellation

Inventive Principle:

Principle #26Copying

2Object-affected harmful factors

If SAW filter is deployed to reject out-of-band blockers, then blocker rejection is improved, but insertion loss increases

Engineering Contradiction:

Improveblocker rejectionVSAvoidinsertion loss

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The transmitter leakage signal, which is normally a harmful blocker, is converted into a useful reference signal by the auxiliary circuit. This leakage signal is captured and processed to create an accurate blocker replica that enables precise cancellation of the harmful blocker from the received signal

Inventive Principle:

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

Solution Approach 2:

The auxiliary circuit acts as an intermediary that captures the transmitter leakage signal and processes it through down-conversion, adjustment, and up-conversion to generate the blocker replica, serving as a mediator between the transmitter and receiver to enable blocker cancellation without requiring physical filtering

Inventive Principle:

Principle #24Intermediary (Mediator)

3Power

If LNA bias current is increased to compensate for lower load resistance, then gain is maintained, but power consumption increases

Engineering Contradiction:

ImproveLNA gainVSAvoidLNA bias current

Core Design Contradiction:

PowerVSUse of energy by moving object

Solution Approach 1:

The LNA output signal is copied through the non-conductive coupling path to create a separate auxiliary signal path. This copying allows the main LNA to operate with optimal impedance matching while the auxiliary path captures the leakage signal for blocker replica generation, eliminating the need to increase LNA bias current

Inventive Principle:

Principle #26Copying

4Productivity

If transmitter and receiver are simultaneously enabled in FDD system, then communication efficiency is improved, but blocker interference increases

Engineering Contradiction:

Improvecommunication efficiencyVSAvoidblocker interference

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The blocker interference is extracted from the received signal by generating a separate blocker replica that represents only the transmitter leakage component. This extracted replica is then subtracted from the received signal, allowing the receiver to operate simultaneously with the transmitter without degradation from blocker interference

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The auxiliary circuit performs preliminary anti-action by capturing the transmitter leakage signal before it interferes with the receiver, processing it to create an accurate blocker replica, and preparing the cancellation signal in advance to counteract the blocker interference before it degrades the received signal

Inventive Principle:

Principle #9Preliminary anti-action

Data Source

PatentUS7773545B2Full division duplex system and a leakage cancellation method

Publication Date: 2010.08.10 MEDIATEK INC

AI summary

An exemplary embodiment of a full division duplex system comprises a receiver, a transmitter and an auxiliary circuit. The receiver receives an inbound RF signal of a first band to generate an inbound baseband signal, and the transmitter up converts an outbound baseband signal by an oscillation signal to generate an outbound RF signal of a second band for transmission. The auxiliary circuit calculates leakages from the outbound RF signal to generate a blocker replica, in which a LNA is coupled to a non-conductive coupling path extended from the input of receiver to collect leakages from the outbound RF signal to produce an induction signal. The induction signal is down converted to perform an adjustment, and thereafter up converted again to generate the blocker replica. In this way, the inbound baseband signal is generated from a subtraction of the inbound RF signal and the blocker replica.