| 摘要 |
An extremely high fidelity digital audio amplifier having a modulator (7) for transforming an analog audio input signal into two complementary trains of pulse width modulated signals for driving power switches (80 and 81), which modulator (7) utilizes a precision triangular waveform to control the transformation. The modulator (7) employs all differential processing without saturated transistors to achieve a minimal distortion modulation system. Upon the occurrence of over-modulation, pulses from the width modulated pulse train produced by the modulator (7) are dropped, and the resulting loss of pulses is detected and fed back to a variable gain amplifier stage (3) of the system. A distortion detection system (5) for detecting the missing pulses utilizes a timing network (60 and 62) to establish the missing pulse period necessary to begin input attenuation of the audio signal by the variable gain amplifier stage (3). A reconstruction filter (13) includes a low-pass section (110) for recovering the amplified audio signal and a notch filter section (101 and 102) having notches centered to eliminate the fundamental of the switching frequency. A variable inductor (121) is employed in connection with a section of the notch filter (101 and 102) for aiding in the proper notching of the signals to maximize surpression of the switching frequency, such inductor (121) being coupled to the feedback network (9), and is adjusted by the operator. |
