Variable-Gain Amplifier Current-Ratio Control for Wider Gain Range
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Solution Overview
Problem
Conventional variable-gain amplifiers have limited gain ranges, requiring cascading of multiple amplifiers which increases power consumption and reduces bandwidth, and are susceptible to performance degradation due to fabrication and temperature variations.
Innovation Solution
A variable-gain amplifier design incorporating a gain controlling circuit with a variable current circuit and differential current circuit, utilizing MOS transistors to control the ratio of input-control current to load current, providing a broader gain range and improved resistance to temperature and fabrication variations through differential driving.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the gain range of a variable-gain amplifier is increased, then the amplifier can accommodate a broader range of signals, but the resistance to fabrication process variation and temperature shift degrades
Solution Approach 1:
The patent implements dynamic gain control by making the transconductance of the input stage variable through control voltages applied to the gates of MOS transistors. This allows the gain to be adjusted continuously while maintaining stability through the differential configuration, resolving the contradiction between broad gain range and resistance to environmental variations.
Solution Approach 2:
The patent changes the operating parameters of the amplifier by varying the control voltages (Vc1 and Vc2) applied to the input stage transistors. This enables continuous adjustment of the transconductance and thus the gain, while the differential configuration ensures that parameter changes are symmetric and resistant to process and temperature variations.
2Adaptability or versatility
If multiple variable-gain amplifiers are cascaded to achieve a broader gain range, then the overall gain range increases, but the power consumption increases and bandwidth is compressed
Solution Approach 1:
The patent merges the functions of multiple amplifiers into a single variable-gain amplifier by implementing a differential input stage where both sides contribute to the gain control. This consolidation achieves a broad gain range in a single stage, eliminating the need for cascading and thereby reducing power consumption while maintaining bandwidth.
3Adaptability or versatility
If multiple variable-gain amplifiers are cascaded to achieve a broader gain range, then the overall gain range increases, but the bandwidth of the amplifying signal is compressed
Solution Approach 1:
The patent implements dynamic gain control in a single stage, allowing the bandwidth to be maintained across the entire gain range. The differential configuration ensures that the signal path remains short and direct, preventing bandwidth compression that would occur with cascaded stages.
Data Source
AI summary
A variable gain amplifier, VGA, and related method are provided. A reference current variably controlled by a control signal is provided, then the reference current is divided to a load current and an input-control current according to differential driving between a constant reference signal and the control signal. Then the input-control current and the load current are used to respectively bias an input stage and an active load of the VGA, such that a gain of the VGA is controlled by a ratio between the input-control current and the load current. In this way, the gain can be controlled by the control signal. The VGA can provide wider gain range and better variable gain characteristics because a sum and a difference of the input-control current and the load current are both controlled by the control signal.