Coded data generation or conversion – Analog to or from digital conversion – Differential encoder and/or decoder
Reexamination Certificate
1999-07-12
2001-05-08
Tokar, Michael (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Differential encoder and/or decoder
C341S143000, C341S141000, C341S139000
Reexamination Certificate
active
06229470
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to electronic systems and in particular it relates to analog clipping circuits for mixed signal codecs.
BACKGROUND OF THE INVENTION
Most prior art codecs are a combination of analog input and digital output. A sigma-delta analog to digital converter (A/D) is scaled for a maximum output corresponding to the +3dbm0 code of the PCM data. The analog signal corresponding to this digital upscale value is far less than the maximum allowable dynamic range, which usually is limited by the supply range. This fact could potentially overload the A/D and consequently the digital filter. An FCC test, mandatory in the U.S., falls under this category. Once the digital filter overloads, internal clipping mechanisms prevent wrap around of the digital signal, thus creating a digital representation of a trapezoidal signal that contains harmonics with sufficient power to increase the FM modulation depth.
SUMMARY OF THE INVENTION
Generally, and in one form of the invention, the mixed signal codec includes: a multiplexer amplifier having an analog output signal; a sigma-delta analog to digital converter having an input coupled to the analog output signal; and a clipping circuit coupled to the input of the analog to digital converter for clipping the analog output signal.
REFERENCES:
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patent: 5821889 (1998-10-01), Miller
patent: 5969654 (1999-10-01), Goldin
patent: 6084467 (2000-07-01), Muza
patent: 6104329 (2000-08-01), Kowano
Sadkowski Roberto
Yang Steve
Brady III Wade James
Stewart Alan K.
Tan V.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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