Programmable Gain Amplifier Calibration Using Digital Gain Trimming
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Solution Overview
Problem
Conventional programmable gain amplifiers face significant gain errors due to resistor mismatches caused by processing and operating condition differences, which are costly to correct using continuous laser trimming and can be inaccurate due to manufacturing stresses.
Innovation Solution
A digital means for trimming and adjusting the gain in programmable gain amplifier circuits using a gain adjust circuit and a gain select circuit, which can boost or cut the gain according to predetermined amounts, utilizing digital control signals and a look-up table to achieve accurate signal amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If continuous laser trimming is used to correct gain errors, then gain accuracy is improved, but manufacturing cost increases
Solution Approach 1:
The patent applies preliminary action by pre-calibrating the programmable gain amplifier during the manufacturing process and storing calibration data in a look-up table. This allows gain accuracy to be corrected in advance without requiring costly continuous laser trimming during operation, thereby improving gain accuracy while reducing manufacturing costs.
Solution Approach 2:
The patent uses a look-up table that contains pre-stored calibration data as a copy of the ideal gain characteristics. Instead of physically trimming the amplifier, the system copies the calibration information into memory and uses digital-to-analog conversion to apply the corrections, replacing expensive physical trimming with cheaper digital storage and retrieval.
2Measurement precision
If laser trimming is used to adjust gain, then gain accuracy is improved, but the process is affected by manufacturing stresses
Solution Approach 1:
The calibration is performed preliminarily during manufacturing under controlled conditions, and the calibration data is stored for later use. This allows the system to compensate for manufacturing stresses that occur after calibration without requiring re-trimming, as the digital correction can be applied consistently regardless of subsequent physical stress effects.
Solution Approach 2:
The patent replaces the mechanical laser trimming process with a digital correction system. Instead of physically altering the amplifier components through laser trimming, the system uses digital-to-analog conversion to apply electronic corrections based on stored calibration data, eliminating the reliability issues associated with mechanical trimming under manufacturing stresses.
3Measurement precision
If resistor values are adjusted to correct gain errors, then gain accuracy is improved, but device complexity increases
Solution Approach 1:
The patent stores calibration data in a look-up table as a digital copy of the required corrections. This approach avoids the need for additional physical resistors or complex analog adjustment circuits, as the correction information is copied into memory and applied through digital-to-analog conversion, thereby improving gain accuracy without significantly increasing device complexity.
Solution Approach 2:
The patent changes the state of the correction from physical (resistor values) to digital (stored calibration data). By storing calibration parameters in a look-up table and using digital-to-analog conversion to apply corrections, the system achieves gain accuracy improvement while maintaining relatively simple circuitry, as digital storage and conversion are standard functions in modern electronic systems.
Data Source
AI summary
A programmable gain amplifier (PGA) circuit includes a gain adjust circuit and a gain select circuit that are both coupled to an output of an amplifier. The gain select circuit completes feedback to the amplifier while the gain adjust circuit is arranged to boost or cut the gain of the gain selection circuit. The gain adjust circuit can be arranged as a trim adjustment to the overall gain of the PGA circuit, where a different trim adjustment can be mapped to each gain setting such as from a look-up table. In other example implementations, the PGA circuit can periodically switch between multiple gain settings using a modulation scheme such that the overall gain is blended between the various gain settings according to a duty cycle, pulse-width, or delta-sigma modulation, with a time averaging effect on the overall gain of the PGA circuit.