Programmable Gain Amplifier Feedback Network for Wide Gain and High CMRR

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Solution Overview

Problem

Existing programmable gain amplifier (PGA) designs require large areas and offer poor performance to achieve a wide range of selectable gain, with challenges in Common Mode Rejection Ratio (CMRR) and power consumption.

Innovation Solution

A resistor network is introduced in the feedback loop, utilizing fewer equivalent resistances to achieve the same gain, reducing the number of critical matching devices and improving CMRR, while also reducing thermal noise and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If traditional resistor networks are used in PGA feedback loops to achieve wide gain range, then gain selectability is improved, but die area increases and matching precision deteriorates

Engineering Contradiction:

Improvegain selectabilityVSAvoiddie area

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent merges multiple resistor functions into a single shared resistor network that serves both differential operational amplifiers. The resistor network includes first, second, third, and fourth resistors that are shared between the two amplifiers, eliminating the need for separate resistor sets and reducing total die area while maintaining programmable gain functionality.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The resistor network is designed to be universal, serving multiple purposes: it provides feedback for both differential operational amplifiers, enables programmable gain through switch selection, and maintains common-mode rejection. The same resistors are used in both feedback paths, making the network multi-functional rather than dedicated to a single amplifier.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If traditional resistor networks are used in PGA feedback loops, then gain range is achieved, but Common Mode Rejection Ratio (CMRR) deteriorates due to poor matching

Engineering Contradiction:

Improvegain rangeVSAvoidCMRR

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

By merging the resistor networks into a shared configuration, all resistors are fabricated in the same location and under the same process conditions, ensuring better matching. The first and second resistors are matched to each other, and the third and fourth resistors are matched to each other, with all four resistors having the same resistance value, which significantly improves CMRR.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent employs homogeneous resistor design where all resistors in the network have the same resistance value and are fabricated using the same process. This homogeneity ensures consistent electrical characteristics and improved matching, directly enhancing CMRR performance across the programmable gain range.

Inventive Principle:

Principle #33Homogeneity

3Adaptability or versatility

If more resistors are used in the feedback loop to achieve programmable gain, then gain selectability is improved, but thermal noise increases

Engineering Contradiction:

Improvegain selectabilityVSAvoidthermal noise

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent reduces the total number of resistors by merging the feedback networks into a shared configuration. Instead of having separate resistor sets for each amplifier, a single set of four resistors serves both amplifiers, reducing the overall resistor count and consequently reducing total thermal noise while maintaining programmable gain functionality.

Inventive Principle:

Principle #5Merging (Combining)

4Adaptability or versatility

If traditional PGA designs are used to achieve wide gain range, then adaptability is improved, but power consumption increases

Engineering Contradiction:

Improvegain rangeVSAvoidpower consumption

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by stationary object

Solution Approach 1:

The shared resistor network reduces the total resistance in the feedback paths, which directly reduces power consumption. By having all four resistors in a shared configuration rather than separate networks, the equivalent resistance is reduced, leading to lower power dissipation while maintaining the same programmable gain range.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS20250105855A1Programmable gain amplifier and a delta sigma analog-to-digital converter containing the pga

Publication Date: 2025.03.27 TEXAS INSTRUMENTS INC

AI summary

A circuit includes an operational amplifier and a resistor network coupled to an output of the operational amplifier. The resistor network includes a first set of resistors coupled between the output of the operational amplifier and a first node of the resistor network, wherein the resistors of the first set are electrically connected in series with each other, a second set of resistors coupled between the first node and a second node of the resistor network, wherein the resistors of the second set are electrically connected in series with each other and include a first number of resistors, a third set of resistors coupled between the second node and a third node of the resistor network, wherein the third node is coupled to a first voltage, and wherein the resistors of the third set are electrically connected in parallel with each other and include a second number of resistors, and a resistor coupled between the first node and the second node and arranged in parallel with the second set of resistors.