Segmented Differential DAC Circuit for Common-Mode Noise Cancellation
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Solution Overview
Problem
D/A converters of resistor string or resistor ladder types introduce thermal noise, which is amplified and output by class-D amplifiers, degrading noise performance in audio systems.
Innovation Solution
A D/A converter structured to convert n-bit digital signals into differential analog signals, utilizing high-order and low-order converters to generate complementary voltages, which are then amplified to produce differential analog signals that cancel out common mode noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a resistor string type or resistor ladder type D/A converter is used, then the D/A converter can be simply structured and manufactured, but thermal noise is generated by the resistors which degrades noise performance
Solution Approach 1:
The patent segments the D/A converter into a high-order converter and a low-order converter, each handling different bit ranges of the digital input signal. This segmentation allows differential output generation from each converter, which when combined, cancel out common mode thermal noise while maintaining the simplicity of resistor-based implementation.
Solution Approach 2:
The patent converts the harmful thermal noise generated by resistors into a beneficial differential signal structure. By generating complementary differential outputs from segmented converters and combining them, the common mode thermal noise components cancel out, transforming the noise-generating resistive structure into a noise-rejecting differential system.
2Device complexity
If conventional single-ended D/A converter is used, then the circuit structure is simple, but the thermal noise is amplified and output by the class-D amplifier
Solution Approach 1:
The patent divides the D/A converter into high-order and low-order segmented converters, each producing differential outputs. This segmentation enables the generation of complementary signals that, when amplified by the class-D amplifier, result in noise cancellation rather than noise amplification.
Solution Approach 2:
The patent inverts the conventional single-ended output approach by implementing differential output generation from segmented converters. The high-order and low-order converters produce inverted/complementary signals that, when combined through the amplifier, cancel out thermal noise instead of amplifying it as in conventional single-ended designs.
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
The proposed solution significantly improves noise performance by canceling out common mode noise, resulting in reduced noise levels and enhanced audio quality.
Implementation Method 1
a high-order converter to generate a first high-order voltage and a second high-order voltage that monotonously change with mutually opposite polarities with respect to high-order m bits of the digital signal
Implementation Method 2
a first amplifier to receive one of the first and the second high-order voltages and one of the first and the second low-order voltages to output one of the differential analog signals
Data Source
AI summary
A high-order converter generates a first high-order voltage VU_P and a second high-order voltage VU_N that monotonously change with mutually opposite polarities with respect to high-order m bits (1≤m<n) of the digital signal. A low-order converter generates a first low-order voltage and a second low-order voltage that monotonously change with mutually opposite polarities with respect to low-order (n−m) bits of the digital signal. A first amplifier receives one of the first and the second high-order voltages and one of the first and the second low-order voltages to output one differential analog signal. Having a configuration in common with the first amplifier, a second amplifier receives another of the first and the second high-order voltages and another of the first and the second low-order voltages to output another differential analog signal.