Envelope Detector Circuit Using VCCS to Cancel Crossover Distortion
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Solution Overview
Problem
Existing envelope detectors suffer from distortion due to temperature and manufacturing process variations, and have inherent crossover characteristics that limit their performance.
Innovation Solution
The envelope detector employs a configuration of voltage-controlled current sources (VCCS) and a current mirror to maintain consistent transfer characteristics despite temperature and manufacturing variations, while also canceling crossover distortions through synchronized voltage-to-current conversions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diode-based envelope detector is used, then the envelope detection function is achieved, but distortion occurs due to threshold voltage and crossover characteristics
Solution Approach 1:
The patent extracts and removes the diode component that causes crossover distortion from the envelope detector circuit. By replacing the diode with a transistor-based voltage-controlled current source, the harmful crossover characteristics are eliminated while retaining the envelope detection functionality.
Solution Approach 2:
The patent changes the operating parameters and characteristics of the detection element by using a transistor instead of a diode. This allows for bias voltage control that keeps the detection element in an active region, avoiding the threshold voltage effects and crossover distortion inherent in diode-based detectors.
2Object-generated harmful factors
If DC bias voltage is adjusted to alleviate distortion, then distortion is reduced, but the solution becomes highly dependent on temperature and manufacturing process
Solution Approach 1:
The patent implements a feedback mechanism through the voltage-controlled current source configuration, where the bias voltage is dynamically adjusted based on the RF signal conditions. This feedback approach automatically compensates for temperature and manufacturing variations, eliminating the need for precise fixed bias voltage settings.
Solution Approach 2:
The patent transitions from a static DC bias voltage approach to a dynamic voltage-controlled current source that adapts its operating point in real-time. This dynamic adjustment ensures optimal performance across varying temperature and process conditions without requiring precise initial biasing.
3Device complexity
If traditional envelope detector components are used, then the circuit is simple, but performance is limited by inherent diode crossover characteristics
Solution Approach 1:
The patent substitutes the passive diode component with an active transistor-based voltage-controlled current source. This substitution replaces the mechanical/electrical diode switching mechanism with a controllable active device that can operate in its linear region, eliminating crossover distortion while maintaining reasonable circuit complexity.
Data Source
AI summary
A method of envelope detection receives an RF (radio frequency) signal comprising a first voltage and a second voltage; converts the first voltage into a first current using a first VCCS (voltage controlled current source); converts the second voltage into a second current using a second VCCS; converts a bias voltage into a third current using a third VCCS; converting an output voltage into a fourth current using a fourth VCCS; sums the first current and the second current into an input current flowing through a first internal node of a first internal voltage; sums the third current and the fourth current into a mirrored current flowing through a second internal node of a second internal voltage; uses a source follower to receive the second internal voltage and output the output voltage; and uses a current mirror to force the mirrored current to be equal to the input current.