Miller Effect Compensation for High Voltage Amplifier Stability

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Solution Overview

Problem

High-voltage monolithic semiconductor circuits face challenges in achieving pole-zero compensation without using capacitors that can withstand high voltages, which are area-intensive, and existing RC networks lead to gain instability due to load conditions.

Innovation Solution

The implementation of a Miller effect stage with a resistor-capacitor (RC) compensation network, where the capacitor can withstand lower voltages, allowing for pole-zero compensation by using a transconductance amplifier and a current mirror circuit to drive the output transistor, effectively reducing the required capacitance and stabilizing the gain.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a capacitor is used to withstand high voltages in the RC compensation network, then the compensation can be achieved, but the silicon area occupied increases significantly

Engineering Contradiction:

Improvevoltage withstanding capabilityVSAvoidsilicon area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The circuit is divided into two functional parts: a high-voltage output stage and a low-voltage compensation stage. The Miller effect stage isolates the compensation capacitor from high voltage by creating a virtual ground at its terminal, allowing the use of low-voltage capacitors that occupy less silicon area while still providing effective compensation for the high-voltage amplifier.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The Miller effect stage acts as an intermediary between the high-voltage output and the low-voltage compensation network. By introducing this intermediate stage with controlled gain, the compensation capacitor operates at reduced voltage stress while maintaining its compensating function, thus reducing the required capacitor size and silicon area.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If the frequency of the compensation pole is reduced to improve stability, then the capacitance value must be increased, but this leads to increased silicon area

Engineering Contradiction:

Improvegain stabilityVSAvoidsilicon area

Core Design Contradiction:

Stability of the object's compositionVSArea of stationary object

Solution Approach 1:

The Miller effect stage introduces a dynamic gain mechanism that allows the compensation network to maintain stability across varying load conditions. The controlled gain of the Miller stage dynamically adjusts the effective compensation, enabling reduced capacitance values while maintaining gain stability that would otherwise require larger capacitors.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

By changing the operating parameters of the compensation network through the Miller effect, the effective compensation pole frequency and capacitance requirements are optimized. The Miller stage transforms the compensation characteristics, allowing smaller capacitance values to achieve the same stability performance that would require larger capacitors in a direct compensation approach.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If a direct RC compensation network is used at the output, then the circuit is simple, but the gain becomes unstable under varying load conditions

Engineering Contradiction:

Improvecircuit complexityVSAvoidgain stability

Core Design Contradiction:

Device complexityVSStability of the object's composition

Solution Approach 1:

The Miller effect stage implements a feedback mechanism where the output voltage is sampled and fed back through the controlled gain stage to the compensation network. This feedback loop stabilizes the gain under varying load conditions by dynamically adjusting the compensation effect, maintaining stability without significantly increasing circuit complexity.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

Instead of directly compensating the full output swing, the Miller effect stage applies partial compensation through its controlled gain, which is sufficient to stabilize the amplifier under varying load conditions. This partial action approach achieves stability with a moderately increased circuit complexity compared to direct RC compensation.

Inventive Principle:

Principle #16Partial or excessive action

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

This approach enables pole-zero compensation in high-voltage circuits using capacitors capable of lower voltages, reducing silicon area occupancy and stabilizing the voltage amplifier gain, thereby enhancing circuit stability.

Implementation Method 1

The circuit may include a Miller effect stage having an input port coupled to the output of the transconductance amplifier and an output port coupled to the gate of the output transistor

Methodology Applied

Scientific EffectMiller effect:

Data Source

PatentUS9479180B2Compensation device for feedback loops, and corresponding integrated circuit

Publication Date: 2016.10.25 STMICROELECTRONICS INT NV

AI summary

An electronic device includes an output terminal, an output transistor having a control terminal and a conduction terminal coupled to the output terminal, and a resistor-capacitor (RC) compensation network configured to act on the control terminal of the output transistor. In addition, the electronic device includes a transconductance amplifier configured to drive the output terminal through the control terminal of the output transistor, and a Miller effect stage coupled to the RC compensation network and having an input port coupled to the transconductance amplifier and an output port coupled to the control terminal of the output transistor.