Amplifiers – With semiconductor amplifying device – Including class d amplifier
Reexamination Certificate
2003-06-03
2004-08-24
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including class d amplifier
C330S298000
Reexamination Certificate
active
06781458
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to providing DC isolation in a switching amplifier or switch mode power supply topology.
A variety of techniques may be employed in switching circuit topologies to provide isolation between relatively high power output devices and the relatively low power circuitry which drives them. Such techniques include capacitive and inductive coupling. One of the challenges associated with such techniques relates to the state of the output device during power up. That is, if the gates of the output devices are left floating while the power supplies are ramping up, the output devices may be conducting during this time. This is particularly undesirable in audio applications in that this often results in an unpleasant popping sound from the loudspeaker being driver by the switching amplifier. In some cases, this transient condition can even be catastrophic to the output devices and/or the load being driven.
It is therefore desirable to provide DC isolation techniques for use in switching circuit topologies which avoid this problem.
SUMMARY OF THE INVENTION
According to the present invention, techniques are provided by which the state(s) of output device(s) in a switching circuit is (are) controlled during power up to avoid the transient condition described above. More specifically, various embodiments of the present invention control the initialization of the gates of such output devices to prevent such transient conditions. According to a specific embodiment, a switching circuit is provided which includes an output switch having a drive terminal and a power supply terminal. Driver circuitry provides a drive signal to the output switch. Isolation circuitry provides DC isolation between the driver circuitry and the output switch. Transient control circuitry controls the drive terminal, thereby keeping the output switch off during stabilization of a supply voltage at the power supply terminal.
According to a more specific embodiment, a switching amplifier is provided which includes first and second output FETs in a half-bridge, single-ended configuration coupled between high side and low side power supply terminals. Driver circuitry provides complementary drive signals to the first and second output FETs. First and second capacitors couple the driver circuitry to the first and second output FETs, respectively, providing DC isolation therebetween. A first clamping transistor is coupled between the gate of the first output FET (e.g., a p-channel device) and the high side power supply terminal. A first RC network is coupled to the high side power supply terminal and is operable to drive the first clamping transistor. A second clamping transistor is coupled between the gate of the second output FET (e.g., an n-channel device) and the low side power supply terminal. A second RC network is coupled to the low side power supply terminal and is operable to drive the second clamping transistor. The clamping transistors and the RC networks are operable to clamp the gates of the output FETs to a high and low side supply voltages at the respective power supply terminals for a predetermined period of time, thereby keeping the output FETs off during stabilization of the high and low side supply voltages.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.
REFERENCES:
patent: 4992751 (1991-02-01), Attwood et al.
“High Voltage Pulsar Circuits”, Supertex inc., VN/VP13 Series Application Note AN-D8, May 16, 2001, pp. 1-4.
“50W Class D Audio Amplifier Evaluation Board” Acoustar, Zetex, ZXCD50STEVAL, Issue 1, Jul. 2002, pp. 1-12.
Beyer Weaver & Thomas LLP
Mottola Steven J.
Tripath Technology Inc.
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