Class-D amplifier with high dynamic range
A class-D amplifier with good signal-to-noise ratio (SNR) performance is shown. The class-D amplifier includes a loop filter, a pulse-width modulation signal generator, a gate driver, a power driver, and a feedback circuit, which are configured to establish a closed amplification loop. The feedback circuit is configured to establish a feedback path. The class-D amplifier further includes a feedback breaker. The feedback breaker breaks the feedback path in response to conditions in which there no-signal information in the class-D amplifier.
1. A class-D amplifier, comprising:
a loop filter, a pulse-width modulation signal generator, a gate driver, a power driver, and a feedback circuit, configured to establish a closed amplification loop, wherein the feedback circuit is configured to establish a feedback path; and
a feedback breaker, breaking the feedback path in response to no-signal information conditions of the class-D amplifier,
wherein:
the feedback breaker includes a logic circuit and a switch circuit;
the no-signal information conditions are detected by the logic circuit; and
when detecting the no-signal information conditions, the logic circuit outputs a switch signal to switch the switch circuit to break the feedback path.
2. The class-D amplifier as claimed in claim 1 , wherein:
an input signal of the class-D amplifier is coupled to the loop filter;
the loop filter is coupled to the pulse-width modulation signal generator;
the pulse-width modulation signal generator generates a first pulse-width modulation signal and a second pulse-width modulation signal;
the gate driver transforms the first pulse-width modulation signal and the second pulse-width modulation signal into control signals;
the power driver is controlled by the control signals to drive a load; and
the feedback circuit is coupled between the power driver and the loop filter to establish the feedback path.
3. The class-D amplifier as claimed in claim 2 , wherein:
in the no-signal information conditions, the first pulse-width modulation signal equals the second pulse-width modulation signal.
4. The class-D amplifier as claimed in claim 3 , wherein:
the logic circuit includes an Exclusive-OR gate that receives the first pulse-width modulation signal and the second pulse-width modulation signal to output the switch signal.
5. The class-D amplifier as claimed in claim 4 , wherein:
the logic circuit is combined into the gate driver.
6. The class-D amplifier as claimed in claim 4 , wherein:
the logic circuit further includes a delay unit, which delays the switch signal according to a response time of the class-D amplifier.
7. The class-D amplifier as claimed in claim 3 , which is a differential-in and differential-out amplifier, wherein:
the feedback circuit includes a first feedback resistor coupled between a positive output terminal of the class-D amplifier and a positive input terminal of the class-D amplifier, and a second feedback resistor coupled between a negative output terminal of the class-D amplifier and a negative input terminal of the class-D amplifier; and
the switch circuit includes a first switch operative to disconnect the first feedback resistor from the positive input terminal of the class-D amplifier, and a second switch operative to disconnect the second feedback resistor from the negative input terminal of the class-D amplifier.
8. The class-D amplifier as claimed in claim 7 , wherein:
the power driver includes an H-bridge circuit.
9. The class-D amplifier as claimed in claim 8 , wherein:
the logic circuit includes an Exclusive-OR gate that receives the first pulse-width modulation signal and the second pulse-width modulation signal to output the switch signal; and
the first switch and the second switch are opened by the switch signal.
10. The class-D amplifier as claimed in claim 9 , wherein:
the logic circuit is combined into the gate driver.
11. The class-D amplifier as claimed in claim 9 , wherein:
the logic circuit further includes a delay unit, which delays the switch signal according to a response time of the class-D amplifier.
12. The class-D amplifier as claimed in claim 3 , which is a single-ended in and single-ended out amplifier, wherein:
the feedback circuit includes a feedback resistor coupled between an output terminal of the class-D amplifier and an input terminal of the class-D amplifier; and
the switch circuit includes a switch operative to disconnect the feedback resistor from the input terminal of the class-D amplifier.
13. The class-D amplifier as claimed in claim 12 , wherein the power driver includes a first transistor, a second transistor, and a third transistor controlled by the gate driver, wherein:
the first transistor is coupled between a power source terminal and the output terminal of the class-D amplifier;
the second transistor is coupled between the output terminal of the class-D amplifier and a negative power source terminal; and
the third transistor is coupled between the output terminal of the class-D amplifier and a common-mode node of the class-D amplifier.
14. The class-D amplifier as claimed in claim 13 , wherein:
the logic circuit includes an Exclusive-OR gate that receives the first pulse-width modulation signal and the second pulse-width modulation signal to output the switch signal; and
the switch is opened by the switch signal.
15. The class-D amplifier as claimed in claim 14 , wherein:
the logic circuit is combined into the gate driver.
16. The class-D amplifier as claimed in claim 14 , wherein:
the logic circuit further includes a delay unit, which delays the switch signal according to a response time of the class-D amplifier.