Differential Driver Common-Mode Control for Supply Ripple Immunity
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Solution Overview
Problem
Differential linear drivers suffer from reduced dynamic range due to asymmetric power supply voltage variations, which cause common-mode noise and ripple, affecting output performance and noise coupling into other circuits.
Innovation Solution
A differential amplifier circuit that sets the common-mode voltage based on the instant maximum value of the input signal, independent of power supply voltages, using a signal maxima detector and common-mode reference circuit to maintain output common-mode voltage symmetry and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fixed common-mode reference voltage is used, then the common-mode voltage is stable, but the dynamic range is reduced due to asymmetric power supply voltage variations
Solution Approach 1:
The patent implements a dynamic common-mode reference voltage that automatically adjusts with power supply voltage variations. The common-mode reference circuit generates a reference voltage that is proportional to the power supply voltage, allowing the differential amplifier to maintain optimal common-mode voltage levels across different operating conditions and maximize dynamic range while preserving stability.
2Object-affected harmful factors
If the common-mode reference voltage is independent of power supply voltages, then noise and ripple are reduced, but the dynamic range is limited by power supply voltage variations
Solution Approach 1:
The patent introduces a common-mode reference circuit as an intermediary between the power supply and the differential amplifier. This circuit generates a common-mode reference voltage that is derived from the power supply voltage itself, creating a proportional relationship that allows the system to maintain noise immunity while adapting to power supply variations and preserving dynamic range.
3Object-affected harmful factors
If a voltage reference is used to provide common-mode reference, then power supply ripple and noise are reduced, but the dynamic range is limited by asymmetric power supply voltage variation
Solution Approach 1:
The patent changes the parameter of the common-mode reference voltage from being fixed and independent of power supply voltage to being variable and proportional to power supply voltage. This parameter change allows the system to maintain the noise-rejection benefits of a voltage reference while adapting to asymmetric power supply variations, thereby preserving dynamic range.
Data Source
AI summary
A differential amplifier provides improved signal swing and reduced common-mode output noise. The differential amplifier circuit includes a driver circuit with a first output for driving a first output of the differential amplifier and with a second output for driving a second output of the differential amplifier. The driver circuit has inputs for receiving a differential (complementary) pair of input signals at least one common-mode reference input for receiving a common-mode reference signal. The differential amplifier also includes a signal maxima detector having inputs for receiving the differential input signals that detects a maximum value between the individual signals, including any input common-mode voltage. The differential amplifier also includes a common-mode reference circuit that provides the common-mode reference signal and an input coupled to an output of the signal maxima detector, so that a common-mode voltage of the outputs is independent of power supply voltages provided to the driver circuit.