Transconductance Amplifier Gain Control With Stable Filter Response
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Solution Overview
Problem
Existing solutions for tuning analog baseband filters and gain control in radio receiver systems face challenges such as large die area consumption, inaccurate adjustments due to component mismatches, and inefficiencies in gain control mechanisms, which affect the performance of transconductance amplifiers and DC offset correction.
Innovation Solution
The proposed solution involves bypassing the baseband filter to adjust its trim capacitor based on a reference signal, using a DCOC DAC to isolate DC offset correction from the RF path, and implementing an AGC circuitry with a constant input impedance to maintain filter response and gain control independently of AGC settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing solutions are used for tuning analog baseband filters and gain control, then the system can operate with filter and gain control functions, but large die area is consumed and component mismatches cause inaccurate adjustments
Solution Approach 1:
The patent segments the baseband filter tuning function from the main signal path by using a separate test signal path. The trim capacitor can be adjusted independently using a test signal without affecting the main RF signal flow, allowing precise adjustment while minimizing die area usage.
Solution Approach 2:
The patent introduces a test signal as an intermediary to facilitate the tuning process. The test signal is injected into the baseband filter through a switch, allowing the trim capacitor to be adjusted independently of the main signal path, thereby improving tuning accuracy without requiring additional large-area components.
2Reliability
If DC offset correction is applied in the RF path, then DC offset can be corrected, but the correction is affected by RF signal variations and consumes more current
Solution Approach 1:
The patent extracts the DC offset correction function from the RF signal path and places it in the baseband path after mixing. This separates the DC correction function from the RF signal, allowing correction to be applied only to the baseband signal without being affected by RF variations, thereby reducing current consumption while maintaining correction effectiveness.
Solution Approach 2:
The mixer output serves as an intermediary stage where DC offset correction is applied after frequency conversion. By correcting DC offset at this intermediate stage rather than in the RF path, the system avoids current consumption associated with RF path correction while maintaining effective DC offset compensation.
3Adaptability or versatility
If AGC circuitry is added to control gain, then gain control is achieved, but the filter response changes with AGC settings
Solution Approach 1:
The patent segments the gain control function into a separate AGC circuitry block that operates independently from the baseband filter. The AGC controls the gain of the transconductance amplifier without affecting the filter's transfer function, allowing gain adjustment while maintaining stable filter response across different AGC settings.
Solution Approach 2:
The patent implements dynamic gain control through AGC circuitry that can adjust the transconductance amplifier's gain based on signal level. The filter remains static while the amplifier's gain varies dynamically, achieving adaptability in gain control while maintaining stability in filter response characteristics.
4Manufacturing precision
If multiple separate circuits are used for filter tuning, DC offset correction, and gain control, then each function can be optimized independently, but device complexity increases
Solution Approach 1:
The patent merges multiple functions (baseband filter, DC offset correction, and gain control) into a single integrated signal path. The test signal injection point is shared across all three functions, allowing them to operate independently while sharing common circuitry, thereby reducing overall device complexity while maintaining individual function optimization.
Data Source
AI summary
A digital to analog converter (DAC) can include a current mode DAC to receive an OC word from digital logic indicating an amount of current to add to or remove from sources of respective transistors of an amplifier and generate a current based on the OC word, an active output stage including a positive current mirror and a negative current mirror to generate a positive current and a negative current based on at least a portion of the generated current, and a plurality of outputs including a plurality of sink outputs and a plurality of source outputs to provide the positive and negative currents to the sources of the respective transistors.