Active Polyphase Filter Using Translinear Conversion for Low-Distortion Gain
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Solution Overview
Problem
Conventional active poly-phase filters suffer from significant transmission loss and distortion when processing high-frequency power, particularly due to the resistor-based differential amplifier, which increases input impedance and reduces gain, making it difficult to maintain linear output power over a wide range and leading to distorted signals at high input powers.
Innovation Solution
The active poly-phase filter incorporates a translinear circuit with a constant current source and multiple transistors to convert unbalanced high-frequency power into difference outputs with a π/2 phase difference, utilizing translinear loops and current mirror circuits to maintain linear conversion across a wide power range and suppress harmonic wave components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a resistor-based differential amplifier is used in the active poly-phase filter, then the circuit can amplify the output signal, but the transmission loss increases and the signal distortion worsens at high power levels
Solution Approach 1:
The patent replaces the resistor-based differential amplifier with a translinear circuit composed of transistors (Q1-Q5) and a constant current source. This substitution eliminates the need for resistors in the signal path, reducing transmission loss and improving linearity at high power levels while maintaining output power amplification capability.
Solution Approach 2:
The patent changes the operating parameters by using transistors biased by a constant current source instead of resistive elements. This parameter change enables the circuit to maintain low transmission loss and high linearity across a wide power range, including high input power conditions where conventional resistor-based amplifiers fail.
2Power
If a resistor-based differential amplifier is used, then the circuit can provide gain, but the input impedance increases making it difficult to maintain linear output power
Solution Approach 1:
The patent substitutes the resistor-based differential amplifier with a translinear circuit using transistors Q1-Q5 and constant current source 25. This replacement provides gain while maintaining low and controllable input impedance, enabling better impedance matching and linear operation across a wide power range.
3Power
If high input power is applied to the resistor-based differential amplifier, then the output power increases, but the signal distortion increases due to non-linear operation
Solution Approach 1:
The patent replaces the non-linear resistor-based differential amplifier with a translinear circuit using transistors and a constant current source. This substitution maintains signal linearity even at high input power levels (e.g., 0 dBm) by utilizing the exponential current-voltage characteristics of the transistors in a translinear configuration, thereby reducing harmonic distortion.
Solution Approach 2:
The patent changes the operating parameters by biasing the transistors with a constant current source, which maintains the transistors in their linear operating region even at high signal power levels. This parameter control ensures that the output power increases with input power while maintaining signal linearity and minimizing distortion.
4Productivity
If conventional active poly-phase filter design is used, then the filter can convert unbalanced power to difference outputs, but harmonic wave components are not sufficiently suppressed
Solution Approach 1:
The patent replaces the conventional resistor-based amplification stage with a translinear circuit using transistors Q1-Q5 and constant current source 25. This substitution effectively suppresses harmonic wave components (particularly even-order harmonics) while maintaining efficient power conversion from unbalanced to difference outputs, due to the symmetric operation and current mirroring in the translinear configuration.
Data Source
AI summary
An active poly-phase filter has a converting section and a filtering section having two first input terminals, two second input terminals and four output terminals. The converting section has first, second, fourth and fifth transistors forming a translinear circuit and a third transistor forming a current mirror circuit with the second transistor. The converting section converts unbalanced high-frequency power into a difference input between a collector current of the third transistor and a collector current of the first transistor having phase difference of π radians. The filtering section receives one collector current at the first input terminals and receives another collector current at the second input terminals and outputs a first difference output between outputs of two output terminals and a second difference output between outputs of other two output terminals such that the difference outputs has a phase difference of π/2 radians.