AC-Coupled Mixer Circuit for Self-Interference Suppression
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Solution Overview
Problem
Communication receiver circuits face challenges in suppressing self-interference from local transmitters, particularly in Frequency Division Multiple Access systems like WCDMA, where stringent filter performance is required to keep second-order intercept point above a certain threshold, making integration with on-chip transceiver circuits difficult.
Innovation Solution
The implementation of a receiver circuit comprising a low-noise amplifier and a mixer circuit with capacitive or inductive coupling, where the coupling capacitors or inductors are sized based on the mixer's transconductance sensitivity to reduce gain imbalance and improve noise rejection, allowing for simplified RF paths and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a suppression filter is placed between the low-noise amplifier and mixer circuit to suppress self-interference, then the second-order intercept point is improved, but the device complexity increases and integration with on-chip transceiver circuits becomes difficult
Solution Approach 1:
The patent extracts the suppression function from a separate physical filter component and integrates it into the mixer circuit's biasing network. By incorporating suppression capacitors (C1, C2) and inductors (L1, L2) directly into the mixer's DC biasing paths, the filter functionality is embedded within the mixer itself, eliminating the need for external SAW filters while maintaining IP2 performance
Solution Approach 2:
The patent merges the suppression filter function with the mixer circuit's biasing network. The same inductors and capacitors that provide DC biasing to the mixer also serve as the suppression filter elements, combining two functions (biasing and filtering) into a single integrated structure that reduces component count and simplifies integration
2Reliability
If a suppression filter with stringent performance characteristics is used to handle small duplex distance, then the second-order intercept point is improved, but the ease of manufacture decreases
Solution Approach 1:
The patent combines the suppression filter function with the mixer circuit's biasing network. The same inductors and capacitors that provide DC biasing to the mixer also serve as the suppression filter elements, combining two functions (biasing and filtering) into a single integrated structure that reduces component count and simplifies integration
Solution Approach 2:
The inductors and capacitors in the mixer biasing network serve dual purposes: providing DC biasing to the mixer and simultaneously acting as suppression filter elements. This multi-functionality eliminates the need for separate filter components and simplifies the manufacturing process
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
This configuration effectively suppresses self-interference, achieves good low-frequency noise rejection, and simplifies RF paths while reducing power consumption, addressing the integration challenges of high-performance filters in on-chip transceiver circuits.
Implementation Method 1
a capacitive coupling circuit comprising matched capacitive coupling circuits to couple an output signal of the low-noise amplifier circuit into quadrature inputs of the quadrature mixer circuit
Implementation Method 2
an inductive coupling circuit. The inductive coupling circuit comprises one or more transformer-coupled inductors configured to couple an output signal of the low-noise amplifier circuit into quadrature inputs of the quadrature mixer circuit
Data Source
AI summary
A method of providing an input signal to a mixer circuit comprises coupling an output signal from a low-noise amplifier circuit to a mixer input of the mixer circuit via an AC coupling circuit, comprising an inductive of capacitive coupling circuit. For capacitive coupling configurations, a coupling capacitor is configured to have a capacitance value determined as a function of a transconductance sensitivity of the mixer circuit. For balanced output configurations of the low-noise amplifier circuit, matched coupling capacitors are used for coupling the balanced output signals to respective inputs of the mixer circuit. In one embodiment, the mixer circuit comprises a quadrature mixer circuit, which may be in a balanced or double-balanced configuration. In another embodiment, the mixer circuit comprises a four-phase mixer circuit, which may be configured as a balanced four-phase mixer circuit coupled to the low-noise amplifier circuit via inductive or capacitive embodiments of the coupling circuit.