Linearized Mixer Input Stage for Third-Order Distortion Cancellation
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Solution Overview
Problem
Standard mixers have a limited small-signal linearity due to their small linear range, which restricts the attainable dynamic range and introduces distortion, especially when handling larger input signals.
Innovation Solution
The mixer design incorporates a differential pair of transistors with a linearizer that cancels third-order distortion terms using transistors Q3 and Q4, and adjustable components like capacitors and resistors to optimize transconductance and phase, allowing for improved input third-order intercept point (IIP3) and wider frequency range operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple differential pair of transistors is used in the input stage, then the device complexity is low, but the small-signal linearity and dynamic range are limited
Solution Approach 1:
The input stage is divided into multiple functional segments: a differential pair for signal reception, a linearizer circuit for distortion cancellation, and a current mode converter. This segmentation allows each segment to be optimized independently, with the linearizer specifically targeting third-order distortion cancellation to improve overall linearity without requiring complete redesign of the entire input stage.
Solution Approach 2:
A linearizer circuit is introduced as an intermediary component between the differential pair and the mixer core. This linearizer acts as a mediator that processes the differential signal and cancels third-order distortion terms before passing the signal to the current mode converter, thereby improving small-signal linearity without significantly increasing the overall device complexity.
2Manufacturing precision
If multi-tanh input cells are used to extend the linear input range, then the small-signal linearity is improved, but the device complexity increases
Solution Approach 1:
The distortion cancellation function is extracted from the main signal path and implemented as a separate linearizer circuit. Instead of using complex multi-tanh input cells that inherently provide linearity, the patent extracts the third-order distortion terms and cancels them separately, achieving extended linear input range with a simpler overall structure.
Solution Approach 2:
The linearizer circuit dynamically adjusts its operation based on the input signal level, changing its effective parameters to cancel third-order distortion. By varying the operating point and gain of the linearizer components, the circuit maintains optimal linearity across a wider input range without requiring the complex structure of multi-tanh cells.
3Adaptability or versatility
If the linearizer components are made adjustable, then the adaptability to different operating conditions is improved, but the device complexity and ease of manufacture worsen
Solution Approach 1:
The linearizer circuit incorporates adjustable components that allow dynamic adaptation to different operating conditions such as frequency and input power level. The adjustability enables the circuit to optimize its distortion cancellation performance for specific applications, with the trade-off of increased component count and manufacturing complexity being accepted for the sake of versatility.
Data Source
AI summary
A mixer includes an input stage to convert an RF input signal to an output signal, and a mixer core to mix the output signal from the input stage with a local oscillator signal. The input stage may include an input cell having a first differential pair of cross-connected transistors, and a linearizer coupled to the input cell. The linearizer may include a second differential pair of transistors having first and second inputs coupled to the input terminals and first and second outputs coupled to the output terminals.