Quadrature Amplifier Feedback Circuit for Fast Start-Up Biasing
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Solution Overview
Problem
Capacitive-feedback amplifiers face issues with d.c. biasing at startup, leading to prolonged time constants and incorrect signal amplification due to charging of input capacitors, which can result in significant errors and long recovery times.
Innovation Solution
The proposed amplifying electronic circuit incorporates a dual feedback resistor and capacitor configuration with start-up capacitors and secondary switches, allowing for synchronous control signals to manage the charging process, reducing the start-up time and correcting amplification errors within a shorter period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switch is used to reset the feedback capacitor before each power-up, then the d.c. biasing problem is solved, but the start-up time becomes excessively long due to the charging of input capacitors
Solution Approach 1:
The patent applies preliminary action by pre-charging the input capacitors through a dedicated charging circuit before the amplifier is activated. The charging circuit includes a charging switch and charging resistor that are activated before the main amplifier switch, ensuring that the input capacitors are already charged when the amplifier starts operating, thus eliminating the slow charging period that would otherwise occur after power-up.
Solution Approach 2:
The patent introduces an intermediary charging circuit that mediates between the power source and the input capacitors. This charging circuit, consisting of a charging switch, charging resistor, and coupling to the power supply, acts as an intermediary mechanism that prepares the input capacitors in advance, separating the charging function from the main amplifier operation and enabling independent control of the charging process.
2Loss of time
If a feedback resistor with high resistance is added to reduce the time constant, then the start-up time is reduced, but the circuit complexity increases
Solution Approach 1:
The patent extracts the charging function from the main feedback network by creating a separate charging circuit with its own switch and resistor. Instead of modifying the feedback resistor to achieve fast charging, the invention removes the charging task from the feedback path and places it in a dedicated preliminary circuit, thus maintaining the feedback network's integrity while achieving fast start-up.
Solution Approach 2:
The patent segments the amplifier startup process into distinct phases: a preliminary charging phase handled by the charging circuit with charging switch and resistor, and the main operation phase handled by the amplifier and feedback network. This segmentation allows each part to be optimized independently - the charging circuit for speed and the feedback network for its primary function.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly reduces the start-up time of the amplifier, ensuring correct signal amplification and minimizing the duration of incorrect output, thereby addressing the d.c. biasing issues and enabling faster power-up and power-down cycles without prolonged error periods.
Implementation Method 1
capacitive-feedback amplifiers, i.e., to use circuit schemes in which an operational amplifier is fed back with a capacitor
Implementation Method 2
using a switch, which is controlled for enabling reset of the circuit formed by the amplifier and by the corresponding feedback network, before each power-up
Implementation Method 3
present on the input terminals of the amplifier is at least one input capacitor, which, whenever the switch is released (i.e., the reset is removed), charges as a function of the value of the signal present at input upon release of the switch
Data Source
Figure 1~4
Figure 2
Figure 3~12
AI summary
An electronic circuit for amplifying signals with two components in phase quadrature, which includes: a feedback amplifier (2) with a feedback capacitor (Cr1); a switch (RESET1) that drives charging and discharging of the feedback capacitor (Cr1) ; an additional capacitor (CRES1) ; and a coupling circuit (RD1, RD2), which alternatively connects the additional capacitor (CRES1) in parallel to the feedback capacitor (Cr1) or else decouples the additional capacitor (CRES1) from the feedback capacitor (Cr1). The switch (RESET1) opens at a first instant (t2), where a first one of the two components assumes a first zero value; the coupling circuit decouples the additional capacitor (CRES1) from the feedback capacitor (Cr1) in a way synchronous with a second instant (t3), where the first component assumes a second zero value.