Temperature Dependent Current Circuit Digital Trimming

Solution Overview

Problem

Current methods for generating a temperature-dependent bias current to reduce temperature drift in analog circuits are limited by the matching and resolution of trimmable current sources, leading to high chip area and power consumption, and are affected by mismatch variations during manufacture, which reduce the accuracy of the bias current.

Innovation Solution

The use of a temperature-dependent current generator with selectively switchable binary converting elements and adjusting elements to digitally convert and adjust signals, allowing for high-resolution bias current generation by separately balancing individual PTAT-CTAT transistor pairs and using gate bias voltages for interpolation, thereby compensating for mismatch errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a network of trimmable current sources is used to generate bias current I(T), then accuracy of bias current control is improved, but chip area and power consumption increase significantly

Engineering Contradiction:

Improvebias current accuracyVSAvoidchip area

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent segments the bias current generation into two separate DACs (PTAT and CTAT) that independently generate temperature-dependent current components. Each DAC is trimmed separately to achieve the desired temperature characteristic, avoiding the need for a complex network of trimmable current sources while maintaining accuracy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts the temperature dependence from the bias current generation by using separate PTAT and CTAT DACs. This allows the temperature characteristic to be achieved through digital-to-analog conversion of temperature-proportional signals rather than through analog trimming of multiple current sources.

Inventive Principle:

Principle #2Taking out (Extraction)

2Measurement precision

If a network of trimmable current sources is used to generate bias current I(T), then accuracy of bias current control is improved, but power consumption increases significantly

Engineering Contradiction:

Improvebias current accuracyVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by stationary object

Solution Approach 1:

The patent segments the bias current generation into two separate DACs (PTAT and CTAT) that independently generate temperature-dependent current components. Each DAC is trimmed separately to achieve the desired temperature characteristic, avoiding the need for a complex network of trimmable current sources while maintaining accuracy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts the temperature dependence from the bias current generation by using separate PTAT and CTAT DACs. This allows the temperature characteristic to be achieved through digital-to-analog conversion of temperature-proportional signals rather than through analog trimming of multiple current sources.

Inventive Principle:

Principle #2Taking out (Extraction)

3Measurement precision

If matching and resolution of trimmable current sources network is improved, then bias current accuracy is improved, but device complexity increases

Engineering Contradiction:

Improvebias current accuracyVSAvoidcircuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the bias current generation into two separate DACs (PTAT and CTAT) that independently generate temperature-dependent current components. Each DAC is trimmed separately to achieve the desired temperature characteristic, avoiding the need for a complex network of trimmable current sources while maintaining accuracy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent replaces the mechanical/analog trimming system with a digital approach. Two DACs convert digital trim codes into analog current components, substituting digital control for analog trimming mechanisms and reducing overall circuit complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS7696909B2Circuit for generating a temperature dependent current with high accuracy

Publication Date: 2010.04.13 TEXAS INSTRUMENTS INC

AI summary

An apparatus for adjusting a first signal with respect to a second signal includes: (a) A first converter receiving the first signal and employing n first converting elements for digitally converting the first signal to at least one first signal element. (b) A second converter coupled with an output, receiving the second signal and employing n second converting elements for digitally converting the second signal to a second representative signal presented at the output. (c) An adjusting element coupled with each of selected of the first converting elements. Each adjusting element is coupled with the output and cooperates with the connected selected element to present a corrected signal element to the output. The output presents an aggregate output signal including contributions from the second representative signal and each corrected signal element. Adjusting is effected by altering at least one corrected first signal element presented to the output.