Pulse modulation type electric power amplifier

Abstract

A pulse modulation type electric power amplifier includes a pulse modulator that receives as input a clock and an input signal, and converts the input signal to a pulse train, an output control circuit that receives as input the pulse train output by the pulse modulator, and controls output of the pulse train, an output circuit that performs switching according to the pulse train output by the output control circuit, a comparator that converts an output terminal voltage of the output circuit to a high or a low digital value, and a short-circuit determination circuit that determines whether an output short circuit has occurred based on a state of an output signal of the comparator, and outputs an output prohibition signal to the output control circuit when an output short circuit is detected. The output control circuit controls output of the pulse train when the output prohibition signal is input, so that the output circuit stops the switching operation. An output short-circuit protection circuit can thereby be configured simply with little circuitry, and is thus small, low power, and integrated easily.

1 .- 12 . (canceled) 
   
   
       13 . A pulse modulation type electric power amplifier comprising:
 a pulse modulator that receives as input a clock and an input signal, and converts the input signal to a pulse train;   an output control circuit that receives as input the pulse train output by the pulse modulator, and controls output of the pulse train;   an output circuit that performs switching according to the pulse train output by the output control circuit; and   a clock detection circuit that detects stoppage of the clock, and outputs an output prohibition signal to the output control circuit when the clock has stopped,   wherein the output control circuit controls output of the pulse train when the output prohibition signal is input, so that the output circuit stops the switching operation.   
   
   
       14 . The pulse modulation type electric power amplifier according to  claim 13 , wherein the clock detection circuit comprises:
 an inverter that receives as input the clock;   an integrator that receives as input an output of the inverter; and   a comparator that detects whether an output of the integrator is within a normal range through comparison with a prescribed reference value, and   outputs the output prohibition signal when the comparator detects that the output of the integrator is outside the normal range.   
   
   
       15 . The pulse modulation type electric power amplifier according to  claim 13 , wherein the clock detection circuit comprises:
 a frequency divider that receives as input the clock;   an integrator that receives as input an output of the frequency divider; and   a comparator that detects whether an output of the integrator is within a normal range through comparison with a prescribed reference value, and   outputs the output prohibition signal when the comparator detects that the output of the integrator is outside the normal range.   
   
   
       16 . The pulse modulation type electric power amplifier according to  claim 14 , wherein the integrator comprises a low pass filter. 
   
   
       17 . The pulse modulation type electric power amplifier according to  claim 15 , wherein the integrator comprises a low pass filter. 
   
   
       18 . The pulse modulation type electric power amplifier according to  claim 13 , wherein
 the output control circuit comprises a first output control circuit that receives as input the output of the clock detection circuit and the output of the pulse modulator, and a second output control circuit that receives as input the output of the clock detection circuit and a signal obtained by inverting the output of the pulse modulator,   the output circuit comprises a first output circuit that receives as input an output of the first output control circuit and a second output circuit that receives as input an output of the second output control circuit, and   the outputs of the first and second output circuits are differential.   
   
   
       19 . The pulse modulation type electric power amplifier according to  claim 13 , wherein the pulse modulator outputs one of a pulse width modulated pulse train, a pulse density modulated pulse train, and a delta-sigma modulated pulse train. 
   
   
       20 . The pulse modulation type electric power amplifier according to  claim 19 , wherein a signal output from the output circuit is an audio signal.