Current-Mode Filter Circuit for Independent Gain and Frequency Control
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Solution Overview
Problem
Existing filter circuits in wireless communication systems face challenges in simultaneously controlling gain and frequency response while maintaining wide bandwidth, as traditional filters like Sallen-Key, BiQuad, and Multiple-Feedback filters struggle with independent adjustment of these parameters, leading to the need for additional programmable gain amplifiers that increase power consumption and reduce system bandwidth.
Innovation Solution
A filter circuit incorporating a current mode programmable gain amplifier with adjustable components for independent control of frequency response and gain, utilizing current extraction elements, current mirrors, and a current-to-voltage converter to generate differential output signals, allowing for simple and efficient handling of input signals and enabling simultaneous adjustment of gain and frequency without affecting each other.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional filters (Sallen-Key, BiQuad, Multiple-Feedback) are used with separate programmable gain amplifiers, then gain control is achieved, but device complexity increases and bandwidth is reduced
Solution Approach 1:
The patent merges the filter and programmable gain amplifier into a single integrated circuit structure. The PGA is embedded within the filter topology, sharing common components such as the operational amplifier and feedback network. This integration eliminates the need for separate PGA stages, reducing overall device complexity while maintaining independent gain control capability through the feedback resistor ratio adjustment.
Solution Approach 2:
The operational amplifier and its feedback network serve multiple functions simultaneously: they provide both the filtering action (through the RC network configuration) and the programmable gain amplification (through the adjustable feedback resistors). This multi-functionality allows a single circuit block to replace what would traditionally require separate filter and PGA stages, thereby reducing device complexity.
2Ease of operation
If traditional filters with separate programmable gain amplifiers are used, then gain adjustment is possible, but system bandwidth is reduced
Solution Approach 1:
By merging the PGA functionality into the filter's feedback network, the signal passes through a single operational amplifier stage rather than cascading through filter output to separate PGA input. This eliminates additional bandwidth-limiting stages and inter-stage coupling, preserving the wide bandwidth characteristics of the original filter design while enabling programmable gain control.
3Adaptability or versatility
If traditional filters are used, then filtering function is achieved, but independent control of gain and frequency response is difficult
Solution Approach 1:
The feedback network is segmented into distinct functional components: the frequency response is controlled by the RC time constant elements (resistors and capacitors connected to the operational amplifier), while the gain is independently controlled by the feedback resistor ratio (Rf1/Rf2). This segmentation allows each parameter to be adjusted through dedicated components without affecting the other, enabling independent control of gain and frequency response.
Solution Approach 2:
The patent employs programmable resistor elements (such as digitally controlled resistors or resistor ladders) that allow the feedback ratio to be changed in discrete steps. This enables electronic programming of the gain value without mechanical switches or potentiometers, facilitating easy and precise adjustment of the gain parameter while the frequency response remains determined by the fixed RC network.
Data Source
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AI summary
A filter circuit (70), comprising a filter (72) and a current mode programmable gain amplifier (74), is provided. The filter circuit (70) is configured to filter an input signal (VF_IN+, VF_IN-, ), resulting in an output signal. The filter (72) is supplied with the input signal (VF_IN+, VF_IN-, ). The filter (72) comprises at least one current extraction element (73), configured to extract a first output current signal. The current mode programmable gain amplifier (74) is configured for receiving and amplifying the first output current signal resulting in an amplified current signal, the output signal is derived from.