Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Reexamination Certificate
2001-07-18
2002-12-10
Jeanpierre, Peguy (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
C341S135000
Reexamination Certificate
active
06492928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to switched capacitor digital-to-analog converters, and, more particularly, to switched capacitor digital-to-analog converters with power-up/down transient suppression for use in audio systems.
2. Description of Related Art
A number of digital sources of audio information are known. These include compact disk players, digital audio tape, digital transmissions and the like. Stereo digital-to-analog converters are also known, which convert the output from such digital sources into analog information for playback. It is common, when dealing with such stereo digital-to-analog converters, that they have a single ended output ranging between a ground or return value and a supply voltage level with a nominal or quiescent value, V
q
, when no signal is applied. It is common in single ended output systems to use a D.C. blocking capacitor to provide a ground centered signal for subsequent processing.
Single-ended digital-to-analog converters (DACs) powered from a single supply can suffer from large transient signals appearing at the outputs when initially powered on. Such DACs present an analog output centered on a nominal quiescent operating voltage, V
q
. The transient occurs when power is applied to the part, and the analog outputs are required to move from ground to V
q
. If this transient occurs rapidly, it can be approximated as a step function, which has energy at all frequencies. On power-up, such a system can suffer an annoying “POP” at the speaker as the DAC initially charges the D.C. blocking capacitor to V
q
.
A similar click or pop can occur when the system is powered off. On entering the power-down state, the charge on the D.C. blocking capacitor remains. When power is removed, the residual charge on the D.C. blocking capacitor discharges rapidly across the load resister resulting in a loud pop.
SUMMARY OF THE INVENTION
In accordance with the invention, digital-to-analog converters provide power-up pop/click transient suppression utilizing a digital transient generator which operates to replace the pop or click, which would otherwise occur, with a smooth transition.
In accordance with another aspect of the invention, a digital-to-analog converter suppresses a pop or a click which would otherwise occur when the DAC is powered down using a current source and a positive feedback amplifier.
In accordance with another aspect of the invention, a digital-to-analog converter automatically switches from a base rate mode to a high rate mode by detecting the ratio of the master clock to the left/right clock.
REFERENCES:
patent: 4695804 (1987-09-01), Bardl et al.
patent: 6005896 (1999-12-01), Maruyama
patent: 6153997 (2000-11-01), Kobayashi et al.
patent: 6236724 (2001-05-01), Labaton et al.
Bocock Richard
Krone Andrew W.
Paulos John J.
Rhode Jason P.
Blakely Sokoloff Taylor & Zaffman LLP
Cirrus Logic Inc.
Jeanpierre Peguy
LandOfFree
Digital-to-analog converter with power up/down transient... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Digital-to-analog converter with power up/down transient..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Digital-to-analog converter with power up/down transient... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2925831