Class-D Triangular-Wave Generator With Stable GBWP and Low Offset
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Solution Overview
Problem
Existing triangular-voltage generators for class-D amplifier circuits suffer from noise contributions, mismatch, and offset factors due to operational amplifiers and MOS transistors, making it difficult to maintain a stable gain bandwidth product (GBWP) independent of process and temperature variations, which affects the amplifier's performance in terms of Power Supply Rejection Ratio (PSRR) and Total Harmonic Distortion (THD).
Innovation Solution
A triangular-voltage generator design that uses an operational amplifier in integrator configuration with selectively couplable input terminals via switches and resistors, forming a divider stage to generate a triangular voltage with a mean value proportional to the high power supply voltage, and an amplitude inversely proportional to the product of resistance and capacitance, minimizing noise and offset by eliminating transistors and current mirrors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If operational amplifiers and MOS transistors are used in the triangular-voltage generator, then the circuit can be implemented with standard components, but noise contributions, mismatch, and offset factors increase, degrading amplifier performance
Solution Approach 1:
The patent extracts and removes the noisy components (operational amplifiers and MOS transistors) from the triangular-voltage generator circuit. The invention replaces these active components with a passive RC oscillator circuit consisting only of resistors, capacitors, and switches, thereby eliminating the noise and offset contributions while maintaining the essential triangular-wave generation function.
2Reliability
If the gain bandwidth product is made independent of process and temperature variations, then amplifier performance (PSRR and THD) is improved, but circuit complexity increases
Solution Approach 1:
The patent creates a simplified copy of the triangular-wave generation function using only passive RC components rather than complex active circuits. By copying the essential oscillation behavior through a simple RC network with switches, the invention achieves temperature and process independence without requiring complex compensation circuits or additional active components.
3Object-affected harmful factors
If transistors and current mirrors are eliminated from the triangular-voltage generator, then noise and offset are reduced, but the ability to control voltage amplitude and frequency may be limited
Solution Approach 1:
The patent achieves voltage amplitude and frequency control by changing the parameters of passive components (resistance values, capacitance values, and switch timing) rather than using active transistor-based control. The RC time constant and switch duty cycle become the control mechanisms, providing sufficient flexibility without requiring transistors or current mirrors.
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 solution provides a substantially constant gain bandwidth product, reducing noise and offset, improving linearity and sensitivity, and adapting to power supply voltage dynamics without degrading amplifier performance, thus enhancing PSRR and THD in class-D amplifier circuits.
Implementation Method 1
an operational amplifier 21, in integrator configuration, having a first input, a second input, and an output supplying a triangular voltage V TRI at a frequency f s and having a mean value equal to V HV /k
Implementation Method 2
The first input of the operational amplifier 21 is selectively couplable to the input terminal IN, via a first switch 23 and a first input resistor R i1 } The first input of the operational amplifier 21 is also selectively couplable to a reference terminal (ground, gnd) by means of a second switch 24 and a second input resistor R i2
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
A triangular-voltage generator (20) for a class-D amplifier circuit (1) has an input terminal (IN) designed to receive a first power supply voltage (VHV) and an output terminal (OUT) designed to supply a triangular-wave voltage (VTRI) having a repetition period (TS), and is provided with an operational amplifier (21) in integrator configuration, having a first input, a second input and an output coupled to the output terminal (OUT). The second input is designed to receive a reference voltage (VREF), as a function of the first power supply voltage (VHV), and the first input is designed to be selectively and alternately connected to the input terminal (IN) during a first half-period (TS/2) of the repetition period (TS), via a first resistor element (Ri1), and to a reference terminal (gnd) during a second half-period (TS/2) of the repetition period (TS), via a second resistor element (Ri2).