Common-Gate Amplifier Body Capacitance Isolation Resistor

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Solution Overview

Problem

The common-gate (CG) amplifier in power amplifiers suffers from degradation in frequency responses due to parasitic body capacitance, which affects reliability and dynamic range, especially when the body terminal is shorted to ground, leading to issues like time-dependent dielectric breakdown and latch-up occurrences.

Innovation Solution

A resistor is coupled between the source and body terminals of the CG amplifier to reduce parasitic body capacitance, improving frequency responses by blocking current through parasitic diodes and pushing non-dominant poles to higher frequencies, thereby enhancing the power amplifier's performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the body terminal of the CG amplifier is shorted to ground, then the body effect is reduced and dynamic range is improved, but parasitic body capacitance degrades frequency response and causes reliability issues

Engineering Contradiction:

Improvedynamic rangeVSAvoidfrequency response

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

A resistor is introduced as an intermediary component between the body terminal and ground, replacing the direct short connection. This intermediary element allows the body terminal to be properly biased while blocking parasitic capacitance paths, thus simultaneously achieving good dynamic range and frequency response without compromising reliability

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the body terminal is directly coupled to the source terminal, then reliability issues like TDDB are reduced, but parasitic body capacitance from diodes degrades frequency response

Engineering Contradiction:

ImproveTDDB resistanceVSAvoidfrequency response

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The harmful parasitic capacitance effect is extracted and blocked by introducing a series resistor in the body terminal path. This resistor selectively blocks the parasitic capacitance paths while maintaining the direct coupling benefit for reliability, thus separating the harmful capacitive effect from the beneficial direct coupling effect

Inventive Principle:

Principle #2Taking out (Extraction)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution effectively reduces parasitic body capacitance, improving the power amplifier's frequency response and power added efficiency, as demonstrated by simulation results showing increased output power and efficiency at 1 dB compression.

Implementation Method 1

parasitic body capacitance from a diode, for example, between a P-Well and the DNW in a p-type substrate or a P-well in an n-type substrate

Methodology Applied

Scientific EffectParasitic capacitance: Parasitic Capacitance

Data Source

PatentUS11558019B2Method and circuit to isolate body capacitance in semiconductor devices

Publication Date: 2023.01.17 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Disclosed is an amplifying circuit and method. In one embodiment, an amplifying circuit, includes: a common-gate (CG) amplifier, wherein the CG amplifier comprises a first transistor, wherein source terminal and body terminal of the first transistor is coupled together through a first resistor.