CMOS AGC Transmitter Circuit for Linear Wide-Range Gain
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Solution Overview
Problem
CMOS transmitter circuits in wireless communication systems face challenges in maintaining a linear relationship between desired gain and amplified signal while minimizing noise, particularly due to the inherent non-linearity of CMOS transistors and the need for a higher gain range that meets WCDMA standards, which is not achieved with existing AGC circuits.
Innovation Solution
A merged mixer and variable gain amplifier circuit is implemented, where the gain transistors operate in the sub-threshold region, and a linearizer circuit generates a temperature-compensated gain control voltage to ensure a linear gain relationship, allowing for a higher gain range of about 90 dB by merging the up-conversion and variable gain circuits and reducing noise through on-chip low pass filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If CMOS transistors are used in transmitter circuits, then manufacturing cost is reduced and ease of manufacture is improved, but the relationship between desired gain and amplified signal becomes non-linear and noise increases
Solution Approach 1:
The patent changes the operating parameters of the CMOS transistors by applying a specific biasing scheme that operates the transistors in a optimized region. The biasing circuit generates a control voltage that compensates for the inherent non-linearity of CMOS transistors, thereby achieving improved gain linearity while maintaining the cost advantages of CMOS technology.
Solution Approach 2:
The patent introduces a biasing circuit as an intermediary component between the control voltage input and the CMOS transistor gates. This biasing circuit acts as a mediator that transforms the control voltage into appropriate gate voltages that linearize the transistor operation, thus resolving the non-linearity issue without changing the fundamental CMOS technology.
2Ease of manufacture
If CMOS transistors are used in transmitter circuits, then manufacturing cost is reduced, but noise is introduced requiring external SAW filter
Solution Approach 1:
The patent converts the harmful noise generated by CMOS transistors into a manageable parameter by using the biasing circuit to pre-compensate for noise-generating operations. The biasing scheme optimizes the operating point to minimize noise generation while maintaining signal integrity, thereby eliminating the need for external noise filtering components.
3Device complexity
If conventional gain range is used, then circuit simplicity is maintained, but gain range is insufficient for WCDMA standards
Solution Approach 1:
The patent implements a dynamic biasing scheme that allows the circuit to adapt its operating characteristics based on the required gain level. The biasing circuit dynamically adjusts the transistor operating points to achieve a wide gain range (exceeding WCDMA requirements) while maintaining circuit simplicity through a unified biasing approach rather than multiple discrete gain stages.
Data Source
AI summary
A CMOS automatic gain control (AGC) circuit that receives an analog control voltage and generates a temperature compensated gain voltage to linearly control the gain of a variable gain circuit operating in the sub-threshold region. A PTAT circuit having a resistor network coupled to a current mirror circuit operating in the sub-threshold region establishes a current having an proportional relationship to temperature. This current is used as a supply for a voltage to voltage converter circuit which generates an intermediate voltage in response to the analog control voltage. A linearizing circuit operating in the sub-threshold region pre-conditions the intermediate voltage, which is then applied to a variable gain circuit. The variable gain circuit is operated in the sub-threshold region, and the preconditioned intermediate voltage will control the amount of gain to be substantially linear with respect to the analog control voltage, and with a range of about 85 dB.