Variable Gain Amplifier Circuit With Dual Emitter Control
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Solution Overview
Problem
Conventional variable gain amplifying circuits have limited gain ranges in each stage, requiring multiple stages to maintain signal integrity, which leads to signal clipping and increased complexity.
Innovation Solution
A variable gain amplifying circuit with two stages, each comprising two BJTs, voltage controlled current sources, and a common voltage-to-current converter, where the variable resistance and current are simultaneously controlled by a control voltage to rapidly adjust gain, providing a wider gain range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the control voltage decreases to reduce gain, then the gain is reduced, but the emitter current becomes very low causing signal clipping
Solution Approach 1:
The patent changes the operating parameters of the BJT by simultaneously adjusting both the emitter current and emitter resistance in response to control voltage changes. This dual parameter adjustment allows the circuit to maintain proper signal levels while achieving the desired gain reduction, preventing signal clipping that would occur with conventional single-parameter adjustment
Solution Approach 2:
The patent implements dynamic adjustment of both emitter current and emitter resistance based on the control voltage signal. This dynamic dual-parameter control allows the circuit to adaptively maintain signal integrity across the full gain range, transforming a static operating point approach into a dynamic coordinated adjustment system
2Device complexity
If conventional variable gain amplifying circuits are used, then the circuit structure is simple, but the gain range of each stage is limited requiring multiple stages
Solution Approach 1:
By simultaneously varying both emitter current and emitter resistance parameters, the patent extends the achievable gain range of each stage without adding circuit stages. This dual-parameter control approach allows a single stage to provide gain adjustment over a range that would conventionally require multiple cascaded stages
Solution Approach 2:
The patent makes each amplifier stage capable of providing both gain adjustment and signal level maintenance functions simultaneously through coordinated emitter current and resistance adjustment. This multi-functionality within a single stage reduces the need for additional stages that would be required in conventional designs
3Adaptability or versatility
If the emitter current is reduced to achieve low gain, then the gain is reduced, but the voltage headroom becomes very small causing signal clipping
Solution Approach 1:
The patent compensates for the loss of voltage headroom by simultaneously adjusting the emitter resistance parameter when reducing emitter current. This coordinated parameter change maintains the necessary voltage levels across the emitter resistor, ensuring sufficient voltage headroom is available even at low gain settings to prevent signal clipping
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 allows for a wider gain range in each stage with fewer stages, preventing signal clipping and maintaining higher emitter currents during low gain, thus enhancing the overall gain range and reducing the need for multiple stages.
Implementation Method 1
two voltage controlled current sources 140, 142... The currents respectively flowing through the voltage controlled current sources 140 and 142 are equal to each other and represented as IE. The current IE of each current source is controlled by a control voltage Vctrl.
Implementation Method 2
a variable resistor with a variable resistance, and the common voltage-to-current converter. The variable resistor with the variable resistance is connected between the emitters of the two BJTs wherein the variable resistance of the variable resistor is represented as RE. The variable resistance RE is controlled by a control voltage Vctrl.
Data Source
AI summary
A variable gain amplifying circuit comprises two stages, a first stage and a second stage with a common voltage-to-current converter. Each stage comprises two BJTs, two voltage controlled current sources, a variable resistor with a variable resistance, and the common voltage-to-current converter. The two BJTs construct a differential amplifier for amplifying a pair of differential signals. The variable resistor with the variable resistance is connected between the emitters of the two BJTs wherein the variable resistance of the variable resistor is represented as RE. The variable resistance RE is controlled by a control voltage Vctrl. The two voltage controlled current sources are respectively connected between the corresponding emitter of BJTs and ground. The currents respectively through the voltage controlled current sources are equal to each other and represented as IE. The current IE is controlled by the common voltage-to-current converter according the control voltage Vctrl. The variable resistance RE and the current IE of the voltage controlled current sources can be varied simultaneously by the control voltage Vctrl so as to rapidly adjust the gain of the variable gain amplifying circuit.