Variable Gain Amplifier Layout That Avoids Input Signal Attenuation
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Solution Overview
Problem
Variable gain amplifier circuits face signal attenuation and impedance changes due to switch on resistance and parasitic capacitance, and require large apparatus size for two-input selectors, making accurate gain adjustment difficult.
Innovation Solution
A variable gain amplifier circuit with parallel amplification portions and switching devices between the amplification coupling line and grounding line, where the switching device is not present in the input signal line, allowing for accurate gain control without signal attenuation and minimizing impedance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If switches are placed in the input signal line to control amplification transistors, then gain can be varied, but signal level is attenuated by switch on resistance and parasitic capacitance
Solution Approach 1:
The patent extracts the switching function from the input signal path by placing switches in the collector circuit instead. The switches (SW1-1 to SW1-n and SW2-1 to SW2-n) control the connection between collector terminals and the output line, completely removing switches from the input signal line (base terminal to collector terminal path), thereby eliminating signal attenuation caused by switch on resistance and parasitic capacitance in the input path.
Solution Approach 2:
The patent introduces collector terminals as intermediary connection points between amplification transistors and the output line. These collector terminals serve as mediators that allow switching control without directly interrupting the input signal path, enabling gain variation while preserving signal integrity through the use of current-controlled switching at the output side.
2Adaptability or versatility
If the number of amplification transistors receiving input signal changes to vary gain, then gain adjustment is achieved, but input impedance changes causing gain adjustment errors
Solution Approach 1:
The patent applies local quality by providing separate biasing circuits (first biasing circuit and second biasing circuit) for different groups of amplification transistors. Each biasing circuit independently controls the base terminals of specific amplification transistors, allowing localized impedance control that compensates for changes in overall input impedance as different numbers of transistors are activated for gain adjustment.
Solution Approach 2:
The patent changes the biasing parameters (base terminal voltages) of amplification transistors dynamically as the number of active transistors changes. The biasing circuits adjust bias voltages to maintain constant input impedance despite variations in the number of amplification transistors receiving the input signal, thereby eliminating gain adjustment errors.
3Ease of operation
If two-input selectors are provided for each amplification transistor to select between received signal and grounding potential, then switching control is achieved, but apparatus size increases
Solution Approach 1:
The patent makes the switches multi-functional by having them perform both the switching function (connecting or disconnecting amplification transistors from the output line) and the grounding function (providing reference potential) simultaneously. Each switch controls both the signal path and the biasing condition, eliminating the need for separate two-input selectors and reducing apparatus size.
Solution Approach 2:
The patent merges the switching control function and the grounding potential selection function into a single switch component. Instead of using two-input selectors that separately choose between signal and ground, the invention combines these functions so that one switch simultaneously controls signal connection and grounding, thereby reducing the number of components and apparatus size.
Data Source
AI summary
A variable gain amplifier circuit with a small-sized configuration can accurately adjust the gain without causing a transmission loss of an input signal. A plurality of amplification portions are connected with each other between an amplification coupling line and a grounding line in parallel. The amplification portion includes a switching device and an amplification transistor, which induces a current corresponding to an input signal to flow between the amplification coupling line and the grounding line via the switching device when the switching device is in the on state. The amplitude gain is varied by, according to a gain control signal, separately switching on and off the switching devices of the respective amplification portions.