Triangular wave generating circuit having synchronization with external clock

A triangular wave generating circuit comprising:

• an integrating unit including an amplifier and a capacitor coupled between an input terminal and an output terminal of the amplifier, the integrating unit providing a triangular wave signal at its output terminal;
• first and second constant current sources for charging and discharging the capacitor;
• a switch unit for coupling of the first and second current sources to the integrating unit to charge and discharge the capacitor in response to an internal clock signal;
• a high/low level limiter comprising a pair of comparators for comparing the output of the integrating unit with upper and lower triangular wave peak limit reference voltages, respectively, and outputting signals indicating when the output of the amplifier coincides with the triangular wave peak limit reference voltages;
• a clock generation unit for providing the internal clock signal in response to the output signals of the comparing unit;
• a synchronizing unit for providing a voltage signal representative of the phase difference between the externally supplied clock pulse and the internal clock signal;
• a low-pass filter for filtering the voltage signal to provide a synchronization voltage signal;
• and
• a reference voltage generator for setting the upper and lower triangular wave peak limit reference voltages to vary a peak to peak swing of the triangular wave signal over time to synchronize the internal clock signal with the externally supplied clock pulse, the reference voltage generator unit setting one of the upper and lower triangular wave peak limit reference voltages to a constant voltage level and the other of the triangular wave peak limit reference voltages to a synchronization voltage.

A Class-D amplifier comprising:

• a modulation stage which generates a pulse-width-modulates (PWM) waveform from an input signal using a triangular wave output from a triangular wave generating circuit;
• and
• an output amplification stage for amplification of an output of the modulation stage, wherein the triangular wave generating circuit comprises:
• an integrating unit including a capacitor, the integrating unit having an output for providing a triangular wave signal;
• first and second constant current sources for charging and discharging the capacitor;
• a switch unit for coupling the first and second current sources to the integrating unit to charge and discharge the capacitor in response to an internal clock signal;
• a comparing unit which compares the output of the integrating unit with upper and lower triangular wave peak limit reference voltages and outputs signals when the output of the integrating unit coincides with the triangular wave peak limit reference voltages;
• a clock generation unit for providing the internal clock signal in response to the comparing unit output signal;
• and
• means for varying a peak to peak swing of the triangular wave signal over time to synchronize the internal clock signal with an externally supplied clock pulse.