Common-Gate Amplifier Body Isolation for Parasitic Capacitance

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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 with either a low or high voltage supply, leading to time-dependent dielectric breakdown and substrate coupling issues.

Innovation Solution

A resistor is coupled between the source and body terminals of the CG amplifier to reduce body capacitance effects, 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

1Device complexity

If the body terminal of the CG amplifier is shorted to ground with a low voltage supply, then the device complexity is reduced, but the threshold voltage increases due to body effect and the dynamic range is reduced

Engineering Contradiction:

Improvebody terminal connectionVSAvoiddynamic range

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

A resistor is introduced as an intermediary component between the body terminal and ground, replacing the direct short connection. This resistor mediates the body effect by controlling the body-to-ground voltage relationship, thereby maintaining dynamic range while keeping the circuit relatively simple.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The body-to-ground voltage relationship is changed from a fixed short (0V) to a controlled relationship through the resistor. By adjusting the resistor value, the body effect parameters can be optimized to maintain threshold voltage stability and dynamic range.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the body terminal of the CG amplifier is shorted to ground with a high voltage supply, then the dynamic range is improved, but the gate terminal becomes susceptible to reliability issues such as time-dependent dielectric breakdown

Engineering Contradiction:

Improvedynamic rangeVSAvoidtime-dependent dielectric breakdown

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The resistor serves as a protective intermediary that limits current flow to the gate terminal while still allowing the body terminal to maintain an appropriate voltage relationship with ground. This prevents excessive current that could cause time-dependent dielectric breakdown.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The resistor is positioned to preemptively protect against harmful current flow before it can cause damage. By controlling the body-to-ground relationship in advance, the circuit prevents the conditions that lead to time-dependent dielectric breakdown.

Inventive Principle:

Principle #9Preliminary anti-action

3Reliability

If direct coupling of the body terminal and source terminal is used, then the body effect is eliminated, but parasitic body capacitance degrades frequency responses such as unit-gain frequency

Engineering Contradiction:

Improvethreshold voltage stabilityVSAvoidunit-gain frequency

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The resistor acts as an intermediary between the body and source terminals, providing a controlled impedance path that reduces parasitic capacitance effects while still maintaining threshold voltage stability. This partial coupling approach balances both requirements.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

Instead of complete direct coupling, the solution applies local quality control by introducing a resistor with specific impedance characteristics. This creates a localized impedance transformation that reduces capacitance effects in the critical frequency path while maintaining the body effect cancellation.

Inventive Principle:

Principle #3Local quality

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 implementation of a resistor between the source and body terminals of the CG amplifier reduces leakage and improves power added efficiency, frequency response, and dynamic range, effectively mitigating the degradation caused by parasitic capacitance, as demonstrated by simulation results showing increased output power and efficiency at 28 GHz.

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

Implementation Method 2

parasitic body capacitance from a diode, for example, between a P-Well and the DNW

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11855590B2Method and circuit to isolate body capacitance in semiconductor devices

Publication Date: 2023.12.26 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.