Variable Gain Amplifier With Constant-Impedance Phase Compensation
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Solution Overview
Problem
In variable gain amplifiers, changes in gain lead to changes in capacitance, resulting in undesirable phase shifts, necessitating a solution to minimize phase changes during gain adjustments.
Innovation Solution
A variable gain amplifier design that includes a first and second variable impedance circuit, transistors, and processing circuitry to adjust gain while maintaining constant imaginary input impedance, thereby minimizing phase changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If gain is changed in a variable gain amplifier, then amplification level is adjusted, but passing phase changes undesirably
Solution Approach 1:
The patent changes the capacitance parameter of the load impedance dynamically to compensate for gain changes. By adjusting the load capacitance in response to gain adjustments, the passing phase is kept substantially constant while the gain can be varied over a wide range (e.g., 0-30 dB).
Solution Approach 2:
The patent employs feedback mechanisms where the gain control signal that adjusts the amplifier gain also controls the variable capacitance of the load impedance. This feedback loop ensures that phase changes are compensated automatically when gain is adjusted, maintaining phase stability throughout the gain adjustment process.
2Adaptability or versatility
If load impedance is made variable to control gain, then gain adjustment range is improved, but phase stability deteriorates
Solution Approach 1:
The patent changes the capacitance parameter of the load impedance dynamically to compensate for gain changes. By adjusting the load capacitance in response to gain adjustments, the passing phase is kept substantially constant while the gain can be varied over a wide range (e.g., 0-30 dB).
Solution Approach 2:
The patent uses a composite impedance structure combining resistive and capacitive elements, where the variable capacitance component works together with the fixed resistance to achieve both wide gain adjustment and phase stability. The composite load impedance (R + j/(ωC)) provides coordinated control of both magnitude and phase characteristics.
Data Source
AI summary
A variable gain amplifier includes a control unit to acquire set gain information related to a setting of a gain, and, on the basis of the set gain information, output a current to a first reference current transistor and a second reference current transistor in such a manner that the sum of the value of a current to the first reference current transistor and the value of a current to the second reference current transistor becomes constant, and output, to a first variable impedance circuit and a second variable impedance circuit, a voltage obtained by multiplying the absolute value of the difference between the value of a current to the first reference current transistor and the value of a current to the second reference current transistor by a coefficient.