Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2001-08-17
2003-02-25
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
Reexamination Certificate
active
06525594
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to electronic systems, and more particularly it relates to audio power amplifiers.
BACKGROUND OF THE INVENTION
A prior art audio power amplifier with PMOS output driver is shown in FIG.
1
. The device of
FIG. 1
includes amplifier
20
, PMOS output driver
22
, NMOS output driver
24
, output coupling capacitor
26
, and resistance
28
which represents a speaker. The backgate diode node
30
of PMOS output driver
22
is connected directly to the supply voltage Vdd. During normal operation, supply voltage Vdd is greater than output voltage Vo. Thus the backgate diode of transistor
22
is normally reverse biased. However, during power down, output voltage Vo can exceed supply voltage Vdd due to the charge stored on capacitor
26
. The backgate diode of transistor
22
then becomes forward biased. This can cause the output coupling capacitor
26
to rapidly discharge, creating an audible pop sound at the speaker
28
.
SUMMARY OF THE INVENTION
Generally, and in one form of the invention, a circuit includes: a transistor; and a switch coupled to a backgate of the transistor for switching between a power supply node and current-path node of the transistor to prevent a voltage on the backgate from dropping below the voltage on the current-path node.
REFERENCES:
patent: 6111455 (2000-08-01), Eleyan et al.
patent: 6333571 (2001-12-01), Teraoka et al.
Arcudia Kenneth L.
Fugate Kevin R.
Brady III W. James
Stewart Alan K.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Zweizig Jeffrey
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