Semiconductor Integrated Circuit Substrate Bias Control
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Solution Overview
Problem
Existing methods for compensating for variations in threshold voltage of MISFETs in semiconductor integrated circuits, such as using replica circuits or simple ring oscillator circuits, are inefficient and lead to performance deterioration due to increased device area and difficulty in controlling delay time.
Innovation Solution
A semiconductor integrated circuit device incorporating a current monitor circuit and a speed monitor circuit with MISFETs of both p-channel and n-channel types connected in series, allowing for precise determination and application of substrate bias voltages to control delay time and threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a replica circuit is formed in the semiconductor integrated circuit device to compensate for threshold voltage variations, then the threshold voltage control precision is improved, but the device area increases
Solution Approach 1:
The patent uses a speed monitor circuit as a simplified copy of the main circuit's delay characteristics. Instead of creating a full replica circuit, the speed monitor circuit captures the essential delay behavior to determine substrate bias voltage, achieving threshold voltage compensation while occupying minimal area.
Solution Approach 2:
The patent extracts only the necessary delay measurement function from the main circuit to create the speed monitor circuit. By separating the delay measurement function into a dedicated simple circuit, the patent achieves precise threshold voltage control without duplicating the entire main circuit structure.
2Area of stationary object
If a simple ring oscillator circuit is used as a delay circuit to compensate for threshold voltage variations, then the device area is reduced, but the delay time control precision deteriorates
Solution Approach 1:
The patent changes the control parameter from direct delay time measurement to delay time ratio measurement. By measuring the ratio between the speed monitor circuit delay and main circuit delay, the patent achieves precise threshold voltage control despite using a simple ring oscillator circuit, as the ratio measurement compensates for circuit complexity differences.
3Reliability
If a delay circuit is formed to determine substrate bias voltage for threshold voltage compensation, then the threshold voltage control is improved, but the device complexity increases
Solution Approach 1:
The speed monitor circuit serves multiple functions: it acts as a delay element for substrate bias determination, provides a reference for delay time measurement, and enables threshold voltage compensation. This multi-functionality reduces the need for separate dedicated circuits, thereby reducing overall device complexity while maintaining compensation effectiveness.
Data Source
AI summary
A semiconductor integrated circuit device has, as a current monitor circuit, a circuit in which n-channel type MISFETs are connected in series with each other. Based on a delay time of a speed monitor circuit in a state where a substrate bias is being applied to the p-channel type MISFETs, a first voltage value of a first substrate bias to be applied to the p-channel type MISFETs is determined. Next, based on a current flowing through an n-channel type MISFET in a state where the first substrate bias is being applied to the p-channel type MISFETs of the current monitor circuit and a second substrate bias is being applied to the n-channel type MISFETs of the current monitor circuit, a second voltage value of the second substrate bias to be applied to the n-channel type MISFETs is determined.