Class-D Amplifier Circuit With Current-DAC Common-Mode Control
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Solution Overview
Problem
Conventional class-D amplifying systems using voltage type DACs and low-pass filters generate noise due to their design, which affects the control of common mode voltage in analog input signals.
Innovation Solution
A class-D amplifying system employing an input current type DAC, a pulse width modulator, an H-bridge power stage circuit, and a common mode current type DAC to generate and adjust common mode voltage, reducing noise and enhancing response speed by correlating the common mode adjustment current with parameters such as common mode voltage, driving power supply, or both, based on signal states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a voltage type DAC and low-pass filter are used in the class-D amplifying system, then the common mode voltage can be controlled, but noise is generated
Solution Approach 1:
The patent extracts and removes the low-pass filter component from the system. By using a current type DAC instead of a voltage type DAC with low-pass filter, the noise-generating filter is eliminated while maintaining the common mode voltage control function through direct current control mechanisms
Solution Approach 2:
The patent changes the fundamental parameter type from voltage to current. By using a current type DAC that directly outputs current signals, the system achieves common mode voltage control without requiring the voltage-type DAC and low-pass filter combination, thereby eliminating the associated noise
2Measurement precision
If a second amplifier is added to control common mode voltage, then the common mode voltage control is improved, but the device complexity and noise increase
Solution Approach 1:
The patent removes the second amplifier from the system configuration. By implementing common mode voltage control through the current type DAC's inherent current output capability, the need for an additional amplifier stage is eliminated, reducing device complexity and associated noise
Solution Approach 2:
The current type DAC performs multiple functions: it converts digital signals to analog current signals while simultaneously providing common mode voltage control through its current output. This multi-functionality eliminates the need for separate control amplifiers, simplifying the overall device structure
3Measurement precision
If linear amplifier circuits are used to control common mode voltage, then the common mode voltage can be adjusted, but the bandwidth and slew rate requirements are not met
Solution Approach 1:
The patent changes the control parameter from voltage to current. The current type DAC directly outputs current signals that can rapidly adjust common mode voltage without being constrained by the bandwidth and slew rate limitations of linear amplifier circuits, achieving faster response speeds
Solution Approach 2:
The patent replaces the linear amplifier circuit (analog voltage control mechanism) with a current type DAC (digital-to-current conversion mechanism). This substitution eliminates the bandwidth and slew rate constraints inherent in linear amplifiers, enabling faster and more precise common mode voltage adjustment
Data Source
AI summary
A class-D amplifying system includes: a first digital-to-analog converter (DAC), a class-D amplifier circuit and a second DAC. The first DAC generates an analog input signal according to a digital input signal. The class-D amplifier circuit generates an output signal according to the analog input signal in a pulse width modulation (PWM) manner. The second DAC generates a common mode (CM) adjustment current for adjusting a CM voltage of the analog input signal according to one or more of the following parameters: (1) the CM voltage of the analog input signal; and/or (2) a driving power. A power stage circuit of the class-D amplifier circuit is powered by the driving power. The second DAC determines which parameter the CM adjustment current is correlated to according to: (A) A level state of the output signal; and/or (B) A level state of a PWM signal of the class-D amplifier circuit.