Programmable Gain Amplifier Resistor Network for Low-Noise Wide Gain
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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 high power consumption and thermal noise due to the need for large equivalent resistance in the resistor network.
Innovation Solution
A resistor network is used in the feedback loop with a configuration of series and parallel resistors, reducing the equivalent resistance and number of critical matching devices, thereby improving Common Mode Rejection Ratio (CMRR) and gain error performance, while also reducing power consumption and thermal noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional resistor networks are used in the feedback loop, then the PGA can achieve a wide range of selectable gain, but the equivalent resistance becomes large leading to increased power consumption and thermal noise
Solution Approach 1:
The resistor network is segmented into multiple discrete resistor units (first plurality, second plurality, third plurality) that can be selectively connected in series or parallel configurations. This segmentation allows the same physical resistors to achieve different equivalent resistance values by changing their connection topology, thereby providing wide gain selection without requiring large equivalent resistance for all gain settings.
2Adaptability or versatility
If traditional resistor networks are used in the feedback loop, then the PGA can achieve a wide range of selectable gain, but the area required on the die increases
Solution Approach 1:
The same set of resistor units serves multiple functions by being reconfigured through different switching states. The resistor network can dynamically change its equivalent resistance value to provide different gain settings, eliminating the need for separate resistor sets for each gain level. This multi-functionality significantly reduces the total die area required compared to traditional designs that would need dedicated resistors for each gain setting.
3Adaptability or versatility
If traditional resistor networks are used in the feedback loop, then the PGA can achieve a wide range of selectable gain, but the number of critical matching devices increases leading to poor CMRR and gain error performance
Solution Approach 1:
The patent applies local quality by making specific resistors (the third plurality of resistors) have precise matched values while other resistors can have broader tolerances. The third plurality of resistors, which are coupled in parallel between the second resistor network node and reference voltage, are the critical matching devices that directly affect CMRR. By concentrating precision requirements on only these local elements rather than all resistors in the network, the design achieves better overall performance with fewer critical matching devices.
Data Source
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.