REDUCTION OF DEAD-TIME DISTORTION IN CLASS D AMPLIFIERS
First Claim
1. A class D output amplifier circuit, comprising:
- a first push-pull output stage, comprising a first pull-up transistor and a first pull-down transistor having conduction paths connected in series between first and second reference voltages and defining a first output node at a connection between the conduction paths, each of the first pull-up and pull-down transistors having control terminals;
a second push-pull output stage, comprising a second pull-up transistor and a second pull-down transistor having conduction paths connected in series between the first and second reference voltages and defining a second output node at the a connection between the conduction paths, each of the second pull-up and pull-down transistors having control terminals;
a first drive circuit, having outputs coupled to the control terminals of the first pull-up and pull-down transistors, and having an input, the first drive circuit for controlling driving its outputs in response to a logic signal at its input in such a manner that, responsive to a transition at its input, the first drive circuit issues signals at its outputs so that both of the first pull-up and pull-down transistors are off for a selected dead-time;
a second drive circuit, having outputs coupled to the control terminals of the second pull-up and pull-down transistors, and having an input, the second drive circuit for controlling driving its outputs in response to a logic signal at its input in such a manner that, responsive to a transition at its input, the second drive circuit issues signals at its outputs so that both of the second pull-up and pull-down transistors are off for a selected dead-time;
a first comparator having a first input for receiving a first differential signal line, having a second input for receiving a reference waveform, having a third input for receiving an offset differential voltage, and having an output coupled to the input of the first drive circuit;
a second comparator having a first input for receiving a second differential signal line, having a second input for receiving the reference waveform, having a third input for receiving an offset signal, and having an output coupled to the input of the second drive circuit; and
offset logic circuitry, having inputs coupled to the first and second drive circuits, and having an outputs for driving an offset signal to the third input of one of the first and second comparators, the offset signal corresponding to a measured time duration in the operation of a corresponding one of the first or second drive circuits.
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Accused Products
Abstract
Pulse-width-modulating class D amplifier with an H-bridge output stage, and method of operating the same. in which output stage dead-time is compensated. Offset logic circuitry detects various dead-time-related conditions at push-pull output drivers, and generates an offset signal applied to the amplified differential input signal, to adjust the time at which the voltage at differential signal lines crosses a ramp reference waveform. The offset signal can correspond to the duration of a disturbance (dead-time at one driver in combination with an active signal at the active driver), or the sum of that disturbance duration with a dead-time at the active driver. The offset signal is generated by charging a capacitor for the duration of this disturbance, or disturbance plus dead-time. According to another approach, error is reduced by charging a capacitor for each transition of the signal for a duration of the dead-time of the active driver. Total harmonic distortion is reduced without requiring increased circuit complexity and without shortening the dead-time to unsafe margins.
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Citations
14 Claims
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1. A class D output amplifier circuit, comprising:
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a first push-pull output stage, comprising a first pull-up transistor and a first pull-down transistor having conduction paths connected in series between first and second reference voltages and defining a first output node at a connection between the conduction paths, each of the first pull-up and pull-down transistors having control terminals; a second push-pull output stage, comprising a second pull-up transistor and a second pull-down transistor having conduction paths connected in series between the first and second reference voltages and defining a second output node at the a connection between the conduction paths, each of the second pull-up and pull-down transistors having control terminals; a first drive circuit, having outputs coupled to the control terminals of the first pull-up and pull-down transistors, and having an input, the first drive circuit for controlling driving its outputs in response to a logic signal at its input in such a manner that, responsive to a transition at its input, the first drive circuit issues signals at its outputs so that both of the first pull-up and pull-down transistors are off for a selected dead-time; a second drive circuit, having outputs coupled to the control terminals of the second pull-up and pull-down transistors, and having an input, the second drive circuit for controlling driving its outputs in response to a logic signal at its input in such a manner that, responsive to a transition at its input, the second drive circuit issues signals at its outputs so that both of the second pull-up and pull-down transistors are off for a selected dead-time; a first comparator having a first input for receiving a first differential signal line, having a second input for receiving a reference waveform, having a third input for receiving an offset differential voltage, and having an output coupled to the input of the first drive circuit; a second comparator having a first input for receiving a second differential signal line, having a second input for receiving the reference waveform, having a third input for receiving an offset signal, and having an output coupled to the input of the second drive circuit; and offset logic circuitry, having inputs coupled to the first and second drive circuits, and having an outputs for driving an offset signal to the third input of one of the first and second comparators, the offset signal corresponding to a measured time duration in the operation of a corresponding one of the first or second drive circuits. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of operating a class D output drive circuit, comprising:
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receiving an input differential signal; generating a differential signal corresponding to the input differential signal at first and second differential signal lines; comparing the voltage at the first differential signal line with a reference waveform to produce a first comparator output signal; comparing the voltage at the second differential signal line with the reference waveform to produce a second comparator output signal; controlling a first push-pull output stage to drive a first output node, coupled to one side of a load, responsive to the first comparator output signal, the controlling comprising enforcing a high impedance state at the first output node for a selected dead-time responsive to transitions of the first comparator output signal; controlling a second push-pull output stage to drive a second output node, coupled to another side of the load, responsive to the second comparator output signal, comprising enforcing a high impedance state at the second output node for a selected dead-time responsive to transitions of the second comparator output signal; wherein a differential voltage appears between the first and second output nodes for a duration corresponding to the input differential signal; and further comprising; adjusting the duration of the differential voltage between the first and second output nodes responsive to a duration of a high-impedance condition at one of the first and second output nodes. - View Dependent Claims (11, 12, 13, 14)
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Specification