Envelope Detector Feedback Circuit for Low-Distortion RF Sensing

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Solution Overview

Problem

Existing envelope detectors suffer from distortion due to temperature and manufacturing process dependencies, and have limitations in speed and accuracy.

Innovation Solution

The envelope detector employs a common-mode source follower, current-controlled current source, and voltage-controlled current source to establish negative feedback control loops, reducing distortion and improving speed and insensitivity to temperature and manufacturing variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a diode is used in the envelope detector, then the envelope detection function is achieved, but distortion occurs due to threshold voltage and crossover characteristics

Engineering Contradiction:

Improveenvelope detection accuracyVSAvoiddistortion level

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent removes the diode component from the envelope detector circuit and replaces it with a combination of transistors (Q1-Q4) configured as source followers and current mirrors. This extraction of the diode eliminates the threshold voltage and crossover distortion inherent to diode-based detectors, while maintaining the envelope detection function through the transistor network.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the operating parameters by using transistors instead of diodes, allowing for bias voltage adjustment through resistors R1 and R2. This parameter change enables operation in a region where threshold effects are eliminated, and the transfer characteristics can be optimized for linearity through the current mirror configuration and feedback mechanisms.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If a DC bias voltage is adjusted to alleviate distortion, then distortion is reduced, but the value becomes highly dependent on temperature and manufacturing process

Engineering Contradiction:

Improvedistortion levelVSAvoidbias voltage stability

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

The patent implements feedback mechanisms through the current mirror configuration (Q2-Q3) and the interconnected source followers. The circuit automatically adjusts current distribution based on the operating point, providing self-regulation that compensates for temperature and process variations. The feedback ensures that the bias conditions remain stable without requiring precise manual adjustment.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The transistor network serves multiple functions simultaneously: it provides biasing, amplification, and distortion compensation. The current mirror configuration not only establishes bias currents but also provides automatic stabilization against temperature and process variations, making the circuit universally robust across different operating conditions without requiring component-specific optimization.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If the diode and output driver are used, then the envelope detection is achieved, but time delay increases reducing the speed

Engineering Contradiction:

Improveenvelope detection functionVSAvoidresponse time

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent replaces the diode-based detection mechanism with a transistor-based active circuit. Transistors have faster switching characteristics and lower junction capacitances compared to diodes, enabling higher speed operation. The source follower configuration provides voltage buffering with minimal phase delay, while the current mirror offers fast current switching, collectively reducing the overall response time of the envelope detector.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Stability of the object's composition

If temperature and manufacturing process variations occur, then the detector performance degrades, but using compensation circuits increases complexity

Engineering Contradiction:

Improvetemperature insensitivityVSAvoidcircuit complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The patent merges the biasing circuitry and temperature compensation functions into the main envelope detection path. The current mirror (Q2-Q3) and source followers are integrated such that they simultaneously perform signal detection and self-compensation for temperature and process variations. This merging eliminates the need for separate compensation circuits, maintaining robustness while avoiding additional complexity.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS12500561B2High-speed low-distortion envelope detector and method thereof

Publication Date: 2025.12.16 REALTEK SEMICON CORP

AI summary

A method of envelope detection operates by receiving a RF (radio frequency) signal having a first voltage at a first node and a second voltage at a second node; using a common-mode source-follower (CMSF) having a first source follower and a second source follower connected in parallel and configured to receive the first voltage and the second voltage, respectively, and jointly output a first current to a third node in accordance with a sum of a second current and a third current received via a fourth node; establishing a first negative feedback control loop by converting the first current into the third current using a current-controlled current source (CCCS); and establishing a second negative feedback control loop by converting a drain voltage at the third node into the second current using a voltage-controlled current source (VCCS).