Source-Follower VGA Gain Control With Low-Power Parallel Paths
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Solution Overview
Problem
Controllable amplifiers in modern communication systems face challenges in achieving low power consumption and high efficiency while maintaining carrier suppression across varying gain and output power levels, particularly in mobile radio systems where battery life is a concern.
Innovation Solution
A controllable amplifier design featuring parallel current paths with transistors connected as source followers, allowing for adjustable gain through control of the second current path via switches or controllable resistors, and the use of additional current sources for varying output impedance, enabling both programmable and analog gain adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If controllable amplifiers are used to vary output power over a wide range, then the output power control capability is improved, but the power consumption increases
Solution Approach 1:
The amplifier is divided into multiple parallel current paths, each with its own transistor connected as a source follower. By selectively activating only the necessary current paths based on the required output power level, the amplifier achieves wide power control capability while minimizing power consumption by keeping unused paths inactive.
2Adaptability or versatility
If the gain factor is varied to control output power, then the output power control is improved, but the carrier suppression deteriorates
Solution Approach 1:
The amplifier employs a dynamic structure where multiple current paths can be selectively activated or deactivated based on the required output power level. This dynamic configuration allows the amplifier to maintain optimal carrier suppression characteristics across different power levels, unlike static gain control methods that compromise suppression performance.
3Measurement precision
If complex calibration is used to maintain accuracy, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The amplifier structure inherently provides accurate gain control through its parallel current path configuration with transistors connected as source followers. This self-organizing structure eliminates the need for complex external calibration procedures, as the circuit automatically maintains accuracy through its design characteristics.
Data Source
AI summary
A controllable amplifier is disclosed. The amplifier includes two current paths which couple an input to an output of the controllable amplifier. Each current path has a respective transistor which is connected as source follower. One of the two current paths is designed to be controllable. It is thus possible to adjust the attenuation and hence the overall gain of the source/follower circuit as a function of a set value for the overall gain (CTRL). The circuit can be used as a variable gain amplifier (VGA), or as a programmable gain amplifier (PGA), in radio-frequency transmitters.