MOS Variable Gain Amplifier With Exponential Gain Adjusting Circuit
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Solution Overview
Problem
Conventional variable gain amplifiers using MOS transistors in WCDMA communication systems face challenges with non-linear current gain, requiring complex gain compensation circuits to achieve exponential linearity, which complicates system design and affects communication quality.
Innovation Solution
A gain adjusting circuit comprising a linear exponential transforming circuit, a voltage buffer circuit, and a power transforming circuit, where the power transforming circuit takes twice the square root of the product of the exponential controlling signal and feedback signal plus the bias current to output a power signal, ensuring a linear-in-dB relationship between the linear controlling signal and current gain, eliminating the need for additional gain compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If MOS transistors are used in the amplifier circuit, then manufacturing cost is reduced and compatibility with CMOS processes is improved, but the current gain becomes non-linear
Solution Approach 1:
The patent changes the operating parameters of the MOS transistors by controlling their working regions. Specifically, it operates the exponential current transforming circuit transistors in sub-threshold regions while keeping voltage buffer circuit transistors in saturation regions, achieving exponential linearity in the current gain without requiring complex compensation circuits
Solution Approach 2:
The patent dynamically adjusts the operating regions of different transistor circuits within the amplifier. By making the exponential current transforming circuit work in sub-threshold region while the voltage buffer works in saturation region, it dynamically optimizes the current gain linearity according to the input signal conditions
2Manufacturing precision
If conventional gain compensation circuits are added to correct non-linear current gain, then current gain linearity is improved, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates the need for complex external gain compensation circuits by incorporating the linearity correction function directly into the amplifier's core transistor operating regions. The sub-threshold operation of the exponential current transforming circuit inherently provides the needed exponential linearity
Solution Approach 2:
The amplifier circuit serves itself by using the inherent characteristics of MOS transistors in sub-threshold region to automatically compensate for gain non-linearity. The circuit's own transistor operating modes provide the correction without requiring separate compensation components
Data Source
AI summary
A variable gain amplifier includes an amplifying circuit and a gain adjusting circuit including the following circuits. A linear exponential transforming circuit transforms a linear controlling signal to output an exponential controlling signal. A voltage buffer circuit is coupled with the linear exponential transforming circuit to receive the exponential controlling signal, outputs a feedback signal to a power transforming circuit, and outputs a voltage controlling signal to control a gain of the amplifying circuit according to the exponential controlling signal and a bias current. A power transforming circuit is coupled with the linear exponential transforming circuit and the voltage buffer circuit to receive the exponential controlling signal and the feedback signal and take two times of a square root of a product of the exponential controlling signal and the feedback signal plus the bias current to output a power signal to the linear exponential transforming circuit.