Linearized Balanced Mixer Using Cross-Coupled Feedback
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Solution Overview
Problem
Gilbert Cell mixer circuits face challenges in maintaining mixer linearity at low supply voltage and low supply power conditions, leading to intermodulation distortion issues, particularly third-order intermodulation distortion, which affects the amplitude and phase of the desired Intermediate Frequency (IF) signal.
Innovation Solution
A balanced mixer circuit design incorporating a differential transconductance amplifier with feedback amplifiers for input and output stages, utilizing cross-coupled transistor pairs to cancel third-order intermodulation distortion, optimizing linearity with minimal gain and supply current cost, and independently adjustable IM3 cancellation at each stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the supply current is decreased to reduce power consumption, then power consumption is reduced, but the mixer linearity deteriorates due to increased intermodulation distortion
Solution Approach 1:
The mixer circuit is divided into multiple independent stages: a first mixer stage and a second mixer stage, each with its own bias current control. This segmentation allows independent optimization of each stage's linearity while operating at low overall power consumption, resolving the contradiction between low power and maintained linearity.
Solution Approach 2:
The invention dynamically adjusts bias current parameters independently for each mixer stage based on operating conditions. By changing the bias current parameter adaptively, the circuit maintains optimal linearity (IIP3) across varying power consumption levels, resolving the fixed trade-off between power and linearity.
2Power
If the gain is increased to improve signal amplification, then signal amplification is improved, but the mixer linearity deteriorates due to increased intermodulation distortion
Solution Approach 1:
The signal amplification function is distributed across multiple mixer stages rather than concentrated in a single high-gain stage. Each stage operates at moderate gain levels, preventing the linearity degradation that occurs in high-gain single-stage designs while achieving overall high signal amplification through cascaded stages.
Solution Approach 2:
The invention employs feedback mechanisms that monitor and adjust the operating parameters of each mixer stage to maintain optimal linearity. This feedback control allows the system to achieve high gain while actively compensating for linearity degradation, resolving the contradiction between gain and linearity.
3Use of energy by moving object
If the supply voltage is decreased to reduce power consumption, then power consumption is reduced, but the mixer linearity deteriorates due to increased intermodulation distortion
Solution Approach 1:
The mixer circuit employs dynamic biasing schemes where the operating point of each stage is adaptively adjusted based on the instantaneous signal conditions and power availability. This dynamic operation allows the circuit to maintain high linearity even at reduced supply voltages, resolving the contradiction between low voltage operation and linearity maintenance.
Solution Approach 2:
The invention changes key operating parameters such as bias currents and transistor sizing ratios to optimize the relationship between supply voltage and linearity. By adjusting these parameters, the circuit achieves acceptable linearity performance at lower supply voltages than conventional designs, resolving the voltage-linearity trade-off.
Data Source
AI summary
Method and apparatus are provided for linearized balanced signal mixing. A signal mixing circuit (10) for translating a radio frequency (RF) signal is provided comprising an input amplifier (12), a mixer network (14), and an output buffer amplifier (18). The input amplifier (12) is configured to produce an amplified RF signal and cancel an input third-order intermodulation (IM3) distortion in the amplified RF signal with a cross-coupled feedback amplifier (13). The mixer network (14) is configured to produce an intermediate frequency (IF) signal based on the amplified RF signal and a local oscillator signal. The output amplifier (18) is configured to buffer the IF signal and cancel an output IM3 distortion in the IF signal with a cross-coupled feedback amplifier (19). The input amplifier (12) and cross-coupled feedback amplifier (13) also serve as a bias current source for the mixer network (14), thus lowering the supply voltage required for the mixing circuit (10).