CMOS Variable Gain Amplifier With Cancellation Current Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional continuously variable amplifiers, such as Gilbert cell type amplifiers, introduce distortion and limit gain range due to step transitions and high harmonic distortion, especially in CMOS processes where high performance bipolar transistors are not available.
Innovation Solution
A CMOS continuously variable gain amplifier design incorporating a cancellation circuit that subtracts a cancellation current from the input terminals of a transconductance circuit, with a control circuit that linearizes the gain control signal and uses separate impedance networks and shunt switches to manage the input signal, reducing distortion and increasing gain range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a shunt circuit is used to control gain in the main signal path, then continuous gain variability is achieved, but total harmonic distortion increases and gain range is limited
Solution Approach 1:
The patent divides the gain control function into two separate circuits: a shunt circuit for mute control and a cancellation circuit for gain control. This segmentation allows each circuit to operate independently, preventing the shunt circuit from introducing distortion while enabling continuous gain adjustment through the cancellation circuit that subtracts current from the input terminals.
Solution Approach 2:
The cancellation circuit acts as an intermediary that introduces a cancellation current to counteract the input signal current. This mediator approach allows gain control to be achieved through current subtraction rather than direct shunting, thereby avoiding the distortion problems associated with shunt circuits in the main signal path.
2Ease of operation
If step transitions are used for gain control, then discrete gain levels are achieved, but distortion such as pop or click is generated
Solution Approach 1:
The patent implements dynamic gain control by continuously adjusting the cancellation current magnitude based on a gain control signal rather than using fixed step transitions. The control circuit dynamically modifies the cancellation current to follow the gain control signal, enabling smooth continuous gain adjustment without generating pop or click distortion.
Solution Approach 2:
The control circuit receives a control voltage and uses feedback mechanisms to linearize the gain control signal, ensuring that the cancellation current magnitude accurately follows the control voltage. This feedback approach prevents distortion by maintaining proper linearization during gain transitions.
3Adaptability or versatility
If Gilbert cell multipliers are used for continuous gain control, then continuous gain variability is achieved, but high performance bipolar transistors are required which are not available in CMOS processes
Solution Approach 1:
The patent replaces the Gilbert cell multiplier architecture (which requires bipolar transistors) with a cancellation circuit using MOS transistors. The cancellation circuit achieves continuous gain control through current subtraction using MOS-based shunt switches and impedance networks, making it compatible with standard CMOS fabrication processes while eliminating the need for high-performance bipolar transistors.
Data Source
AI summary
An apparatus and method are provided. Generally, an input signal is applied across a main path (through an input network) and across a cancellation path (through a cancellation circuit). The cancellation circuit subtracts a cancellation current from the main path as part of the control mechanism, where the magnitude of the cancellation current is based on a gain control signal (that has been linearized to follow a control voltage).