Differential RF Amplifier With Cross-Coupled Common-Mode Rejection
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Solution Overview
Problem
Existing differential RF amplifiers fail to achieve good common mode rejection while maintaining acceptable linearity and low noise, leading to high current consumption and increased costs.
Innovation Solution
The RF amplifier design incorporates a differential pair of transistors with cross-coupled capacitors and resistors, creating a loop that balances common mode signals and reduces AC current needed, thereby achieving high common mode rejection and linearity with low noise and reasonable current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional RF amplifier designs are used, then common mode rejection can be improved, but linearity deteriorates
Solution Approach 1:
The amplifier is divided into two separate branches (first and second branches) with independent transistors, resistors, and capacitors. Each branch processes one signal of the differential pair, allowing independent optimization of common mode rejection in each branch while maintaining overall linearity through the differential configuration.
Solution Approach 2:
The patent introduces asymmetric elements through the cross-coupled capacitors (first and second capacitors) that connect opposite branches. This asymmetric coupling creates differential feedback that enhances common mode rejection while the symmetric differential pair structure preserves linearity. The resistors in each branch are configured asymmetrically relative to the signal flow but symmetrically in the differential configuration.
2Manufacturing precision
If higher current consumption is used, then linearity can be improved, but noise increases
Solution Approach 1:
The patent implements feedback through cross-coupled capacitors that connect the output of one branch to the input of the opposite branch. This feedback mechanism linearizes the amplifier operation by correcting non-linear distortions without requiring increased current consumption, thereby maintaining low noise performance while improving linearity.
Solution Approach 2:
The amplifier utilizes dynamic balancing through the differential pair configuration where the two branches operate in opposition. This dynamic balance allows the circuit to maintain high linearity at lower current levels by exploiting the differential cancellation of non-linear effects, reducing noise generation compared to single-ended high-current designs.
3Measurement precision
If more components are added to improve common mode rejection, then device area increases
Solution Approach 1:
The patent merges multiple functions into shared components. The cross-coupled capacitors simultaneously provide common mode rejection, frequency compensation, and stability control. The resistors in each branch serve both as load elements and as part of the common mode rejection network. This functional merging achieves high common mode rejection without proportionally increasing device area.
Solution Approach 2:
Each component in the amplifier serves multiple purposes. The transistors provide both signal amplification and common mode rejection through their differential configuration. The capacitors provide frequency compensation, stability, and common mode signal blocking. The resistors serve as loads and participate in common mode rejection. This multi-functionality reduces the need for additional dedicated components, minimizing device area while achieving high common mode rejection.
Data Source
AI summary
An RF amplifier including first and second branches coupled in parallel between first and second supply voltage terminals, and a differential pair including first and second transistors each having first and second main current terminals, the second main current terminal of the first transistor being coupled by a first capacitor to the first main current terminal of the second transistor, and the second main current terminal of the second transistor being coupled by a second capacitor to the first main current terminal of the first transistor, wherein the first branch includes a first resistor coupled between the first main current terminal of the first transistor and the second capacitor, and the second branch includes a second resistor; coupled between the first main current terminal of the second transistor and the first capacitor.