Differential Envelope Detector With Common-Mode Feedback Bias Stability
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Solution Overview
Problem
Conventional envelope detectors for asynchronous communication using ultra-high frequency shortwave carrier signals and pulse amplitude modulation suffer from DC offset issues due to temperature changes and require additional single-differential signal conversion circuits, leading to potential noise and instability.
Innovation Solution
A differential envelope detector with common mode feedback that includes input and output terminals, amplification units, and feedback mechanisms to stabilize DC voltages, minimizing temperature influence and eliminating the need for additional signal conversion circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single-differential signal conversion circuit is added to convert the single output signal of the ED into differential signals, then the differential output structure is achieved, but a DC offset occurs between gate voltages of the transistors and the DC offset increases as the single output signal increases
Solution Approach 1:
The patent introduces a feedback mechanism where the single output signal of the envelope detector is fed back to the common gate terminal of the differential pair through a feedback resistor. This feedback stabilizes the common gate voltage, preventing DC offset variations that would otherwise occur with changing output signal levels. The feedback loop automatically adjusts the common gate voltage to maintain proper biasing conditions.
Solution Approach 2:
The patent employs a current mirror circuit configured to maintain equal potentials at the gate terminals of the differential pair transistors. The current mirror ensures that both gates remain at the same DC potential level, eliminating DC offset between the gates. This equipotential configuration works in conjunction with the feedback mechanism to stabilize the differential output.
2Device complexity
If the conventional ED structure with single output is used, then the circuit is simpler, but an additional single-differential signal conversion circuit is required at the next stage
Solution Approach 1:
The patent combines the envelope detection function with the differential signal generation function into a single integrated circuit. The envelope detector inherently produces a differential output through its differential pair configuration, eliminating the need for a separate single-differential conversion circuit at the next stage. This merging reduces the overall system complexity while maintaining signal compatibility.
Solution Approach 2:
The envelope detector circuit is designed to perform multiple functions: it detects the envelope of the input signal while simultaneously providing a differential output that can directly interface with subsequent differential circuits. The differential pair configuration serves both as the core detection element and as the differential signal source, making the circuit universal and eliminating the need for additional conversion stages.
3Power
If the single output signal level increases, then the signal strength is improved, but the DC offset between gate voltages increases
Solution Approach 1:
The feedback resistor connects the single output terminal to the common gate terminal, creating a feedback loop that automatically compensates for changes in output signal level. When the output signal increases, the feedback mechanism adjusts the common gate voltage to maintain proper biasing, preventing DC offset increases. This feedback stabilization allows the output signal strength to increase without compromising gate voltage stability.
Data Source
AI summary
The present invention relates to a differential envelope detector, which comprises: input terminals for separating cathode and anode components from a signal and receiving same; a first voltage output unit for outputting a first common mode voltage between the input terminals; a first amplification unit, which receives an input signal as a differential pair and amplifies same so as to output a first output signal; a second amplification unit, which receives the first common mode voltage so as to output a second output signal; and a second voltage output unit for outputting a second common mode voltage between a constant current source unit and an output terminal, wherein the output size of the detector is hardly affected by temperature changes, and an output DC voltage is also fixed so as to be effective with respect to input bias of the next stage amplifier.