Signal Conversion Circuit With Source Follower for Rail-to-Rail Input

Solution Overview

Problem

Existing signal conversion circuits for differential voltage signals face challenges in achieving high-speed operation while minimizing circuit area and current consumption, particularly in low-voltage interfaces where rail-to-rail input is required, due to constraints on transistor load capacitance and the need for multiple amplifier circuits.

Innovation Solution

The proposed signal conversion circuit employs a combination of NMOS and PMOS transistors with a current source and resistors to form a differential amplifier and source follower configuration, allowing for operation in multiple modes based on input voltage levels, thereby reducing circuit complexity and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If two differential amplifier circuits are used to convert input common-mode voltage, then rail-to-rail input operation is achieved, but circuit area increases and current consumption increases

Engineering Contradiction:

Improverail-to-rail input operationVSAvoidcircuit area

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent combines a differential amplifier circuit and a source follower circuit into a single integrated circuit. The differential amplifier converts the input common-mode voltage, while the source follower provides additional voltage buffering and extends the input voltage range. This merging allows rail-to-rail input operation to be achieved without requiring two separate differential amplifier circuits, thereby reducing circuit area and current consumption while maintaining the adaptability for wide voltage range operation

Inventive Principle:

Principle #5Merging (Combining)

2Adaptability or versatility

If two differential amplifier circuits are used to convert input common-mode voltage, then rail-to-rail input operation is achieved, but current consumption increases

Engineering Contradiction:

Improverail-to-rail input operationVSAvoidcurrent consumption

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The patent combines a differential amplifier circuit and a source follower circuit into a single integrated circuit. The differential amplifier converts the input common-mode voltage, while the source follower provides additional voltage buffering and extends the input voltage range. This merging allows rail-to-rail input operation to be achieved without requiring two separate differential amplifier circuits, thereby reducing circuit area and current consumption while maintaining the adaptability for wide voltage range operation

Inventive Principle:

Principle #5Merging (Combining)

3Adaptability or versatility

If transistor load capacitance is increased to handle broader voltage range, then voltage conversion capability is improved, but operating speed decreases

Engineering Contradiction:

Improvevoltage conversion capabilityVSAvoidoperating speed

Core Design Contradiction:

Adaptability or versatilityVSSpeed

Solution Approach 1:

The patent segments the voltage conversion function into two distinct circuits: a differential amplifier circuit for common-mode voltage conversion and a source follower circuit for voltage buffering and extension. Each circuit is optimized for its specific function with appropriately sized transistors and capacitances. The differential amplifier handles the core voltage conversion with minimal capacitance for high speed, while the source follower extends the voltage range without significantly impacting the overall operating speed, thus resolving the contradiction between voltage conversion capability and operating speed

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS7812645B2Signal converting circuit

Publication Date: 2010.10.12 THINE ELECTRONICS

AI summary

A signal conversion circuit 2 comprises a differential amplifier portion 10 and a source follower portion 20. When differential voltage signals INp and INn are input to a first input terminal 5 and second input terminal 6 respectively, operations occurs either in a mode in which only the differential amplifier portion 10 operates, or a mode in which both the differential amplifier portion 10 and the source follower portion 20 operate, or a mode in which only the source follower portion 20 operates, according to the levels of the differential voltage signals INp and INn. The differential amplifier portion 10 and source follower portion 20 have fewer components compared with a circuit comprising two differential amplifier circuits. By this means, the circuit area can be reduced, and in addition current consumption can be reduced. Also, because the source follower portion 20 performs non-inverting amplification of the differential voltage signals INp and INn, high-speed operation is possible.