Class-d-power-amplifier

Description: In this circuit, a 2-MHz clock is divided by eight in U1, resulting in a stable 250-kHz carrier. Q1 and Q2 buffer the clock, providing a low-impedance drive for operational amplifier U4, which functions as a high-gain amplifier and integrator. U4 accepts audio inputs and transforms the 250-kHz square wave into a triangular wave. The combined audio and triangular-wave signal is fed into comparator U7, where it is compared with a defined reference to generate a pulse-width modulated signal at the output of U7. The output devices operate between the +50 V and -50 V power rails in a complementary manner, driving an output filter that is a sixth-order Butterworth low-pass type, which demodulates the audio while attenuating the carrier and high-frequency components. Feedback is provided by resistor R1, and the amplifier gain is determined by the ratio of R1 to R2. Specifications include 200 W continuous power into a 4-ohm load, a frequency response of 20 to 20 kHz with +0.5, -1.0 dB at 200 W, total harmonic distortion (THD) of less than 0.5% at 200 W, a 1.5-V rms input for rated output, a 69 dB signal-to-noise ratio with A-weighting, and a slew rate of 6.6 V/ms.

The circuit operates as a high-efficiency audio amplifier utilizing pulse-width modulation (PWM) for signal processing. The initial clock signal generated at 2 MHz is effectively divided down to 250 kHz to serve as the carrier frequency. The use of Q1 and Q2 as buffer stages ensures that the clock signal is delivered with low impedance, which is critical for maintaining signal integrity when interfacing with U4. The operational amplifier U4 plays a pivotal role in shaping the audio signal; by integrating the square wave from the clock into a triangular waveform, it prepares the signal for further modulation.

Comparator U7 is essential for PWM generation, where it compares the processed audio signal against a reference voltage. This comparison results in a modulated output that varies in width according to the amplitude of the audio input, allowing for efficient amplification while minimizing power losses. The output stage employs complementary switching devices, which alternate between the positive and negative supply rails, thus enhancing efficiency and reducing heat generation.

The sixth-order Butterworth low-pass filter is designed to effectively demodulate the PWM signal, ensuring that the audio output is clean and free from high-frequency artifacts associated with the modulation process. The feedback mechanism through R1 is critical for maintaining stability and ensuring the desired gain of the amplifier, which is determined by the ratio of R1 to R2. This configuration allows for precise control over the amplifier's response characteristics.

With a continuous power output of 200 W into a 4-ohm load, the amplifier is capable of delivering high-quality audio across the specified frequency range. The performance metrics, including low total harmonic distortion and a favorable signal-to-noise ratio, indicate that the circuit is well-suited for high-fidelity audio applications. The specified slew rate further supports the amplifier's ability to handle rapid changes in signal amplitude, making it appropriate for dynamic audio sources. Overall, this circuit exemplifies an effective design for a high-power audio amplifier utilizing advanced modulation techniques.In this circuit, a 2-MHz clock is divided by eight in Ul, providing a stable 250-kHz carrier. Ql and Q2 buffer the clock and provide a low-impedance drive for op amp U4, which is a high-gain amplifier and integrator. U4 accepts audio inputs and converts the 250-kHz square wave into a triangular wave. The summed audio and triangular-wave signal is applied to the input of comparator U7, where it is compared with a de reference to produce a pulse-width modulated signal at the output of U7.

The output devices switch between the +50 V and -50 V rails in a complementary fashion, driving the output filter that is a sixth-order Butterworth low-pass type, which demodulates the audio and attenuates the carrier and higli frequency components. Feedback is provided R1; amplifier gain is R1R,. Specifications: 200 W continuous power into a 4-flload; 20 to 20kHz frequency response +0.5, -1.0 dB at 200 W; THD, !MD (";; 0.5% at 200 W; 1.5-V rms input for rated output; 69 dB SIN ratio, A weighting; 6.6-V ms slew rate.