Active Polyphase Filter Circuit to Suppress Pass Loss
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Solution Overview
Problem
Conventional polyphase filters experience pass loss when suppressing image disturbing waves due to their use of passive resistors.
Innovation Solution
The use of transistors to amplify input signals and form differential signals, which allows for the suppression of pass loss while maintaining 90-degree phase difference characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive resistors are used in the polyphase filter to suppress image disturbing waves, then the frequency band can be limited and image rejection is achieved, but pass loss occurs in the signal path
Solution Approach 1:
The patent changes the fundamental parameter of the filtering element from passive resistor to active transistor-based circuit. This parameter change enables the filter to provide signal attenuation for image frequencies while simultaneously providing gain for the desired signal band, thereby eliminating pass loss while maintaining image rejection capability.
Solution Approach 2:
The patent replaces the passive resistive mechanism with an active transistor-based mechanism. The transistor circuit uses controlled current flow and transconductance to achieve filtering functionality, substituting the traditional passive mechanical/electrical resistance-based approach with an active semiconductor-based approach that can provide both filtering and amplification.
2Loss of energy
If transistors are used to amplify signals and eliminate pass loss, then pass loss is suppressed and gain is provided, but the device complexity increases compared to passive resistor-based filters
Solution Approach 1:
The transistor-based filter circuit performs multiple functions simultaneously: it provides signal amplification for the desired band, attenuates image frequencies, and eliminates pass loss. This multi-functionality consolidates what would traditionally require separate amplifier and filter stages into a single integrated circuit, thereby managing complexity while achieving multiple objectives.
Solution Approach 2:
The patent merges the filtering function and amplification function into a single integrated transistor-based circuit. Instead of using separate passive filter components and active amplifier components, the design combines these functions in one circuit topology, reducing the overall number of discrete components and interconnections.
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 effectively suppresses pass loss and allows for adjustable characteristics, including gain, by utilizing transistors with transconductance to manage signal amplitudes and phases.
Implementation Method 1
a first transistor amplifying a first I signal inputted from a first input terminal
Data Source
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AI summary
A first transistor (2a), a second transistor (2b), a third transistor (2c) and a fourth transistor (2d) are provided. A first transistor (2a) amplifies a first I signal VIP inputted from a first input terminal (1a). A second transistor (2b) amplifies a first Q signal VQP inputted from a second input terminal (1b). A third transistor (2c) amplifies a second I signal VIN when the second I signal VIN is inputted from a third input terminal (1c), the second I signal VIN forming a differential signal with the first I signal VIP. A fourth transistor (2d) amplifies a second Q signal VQN when the second Q signal VQN is inputted from a fourth input terminal (1d), the second Q signal VQN forming a differential signal with the first Q signal VQP.