Switched Gain-Controlled Amplifier With Negative Gain and High Linearity
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Solution Overview
Problem
Gain-controlled amplifiers typically face a trade-off between linearity, response speed, and gain controllability, often sacrificing one for the others, and lack the ability to provide negative gain.
Innovation Solution
A gain-controlled amplifier design incorporating switches, transistors, current mirrors, and resistive networks with taps, allowing for high linearity and fast response speed while enabling negative gain through a voltage-to-current converter and symmetric resistive networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an operational amplifier is used to implement the gain-controlled amplifier, then high linearity is achieved, but response speed deteriorates
Solution Approach 1:
The amplifier is divided into multiple parallel paths: a first amplification path with a first transistor and first resistive network for high-linearity amplification, and a second amplification path with a second transistor and second resistive network for fast response. This segmentation allows each path to be optimized for its specific function while working together to achieve both high linearity and fast response speed.
Solution Approach 2:
The circuit dynamically switches between different amplification paths based on operating conditions. Switches control the connection of different transistor-resistive network pairs, allowing the system to adaptively select the optimal path (high-linearity path or fast-response path) or combine them, thus dynamically optimizing performance rather than being fixed in one configuration.
2Speed
If the gain-controlled amplifier is designed for high linearity and fast response speed, then these performance parameters are improved, but the ability to provide negative gain is lost
Solution Approach 1:
The circuit uses asymmetric current mirroring and resistive network configurations to achieve negative gain. The first and second current mirrors are configured with different reference currents (first reference current and second reference current), and the resistive networks have different tap configurations, allowing the output to be inverted relative to the input under certain switch states, thus providing negative gain capability.
Solution Approach 2:
The same amplifier circuit structure can provide both positive and negative gain through switch control. The switches can route signals through different paths and configurations, making the single circuit capable of multiple gain modes (positive gain, negative gain, different gain magnitudes) without requiring separate dedicated circuits for each function.
3Adaptability or versatility
If switches are used for gain control, then gain controllability is improved, but linearity deteriorates due to switch impedance non-linearity
Solution Approach 1:
Current mirrors are introduced as intermediary elements between the switches and the amplification paths. The current mirrors convert the switching actions into precise current relationships that are less sensitive to switch impedance variations. This intermediary mechanism helps maintain linearity by providing a more stable and predictable current transfer ratio even when switch impedances vary non-linearly.
Data Source
AI summary
A gain-controlled amplifier is disclosed including: a set of switches; first and second transistors whose second terminals are coupled to each other via a resistive element; a first current mirror, coupled to a first terminal of the first transistor, for providing a set of first currents; a second current mirror, coupled to a first terminal of the second transistor, for providing a set of second currents; a first resistive network, coupled to the second terminal of the first transistor via a current source, for providing a first output signal; and a second resistive network, coupled to the second terminal of the second transistor via another current source, for providing a second output signal. Both the first and second resistive networks have a plurality of taps, coupling to either a first current or a second current through a switch of the set of switches.