One-bit analog-to-digital converters and digital-to-analog converters using an adaptive filter having two regimes of operation
First Claim
1. An adaptive one-bit audio digital-to-analog converter comprisingcombining means receiving input dam pulses applied to the converter and signals from a negative feedback path for additively combining the input signals and the negative feedback path signals, andsignal path means includinga forward path receiving the output of said combining means and providing at its output the output of the converter and the input to the negative feedback path, anda negative feedback path coupling the output of said forward path to said combining means,said signal path means further including a variable gain amplifier and a filter having a fixed frequency-dependent response, said combining means and signal path means forming an adaptive low-pass filter having two regimes of operation, one in which the characteristic is that of a low-pass filter with a fixed cut-off frequency but with variable passband gain and another in which the characteristic is that of a low-pass filter with a variable cut-off frequency but a fixed passband gain.
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Abstract
One-bit analog-to-digital converters (ADCs) and digital-analog-converters (DACs) employ an adaptive filter. The filter has two regimes of operation: variable gain within the passband of the filter under low-level signal conditions and fixed gain but a variable filter cutoff frequency (sliding band) under high-level signal conditions. Thus, excessive low-frequency gain under no-signal conditions is avoided and, when implemented using a voltage controlled amplifier (VCA), the arrangement does not demand less offset from the VCA under low-level signal conditions.
26 Citations
7 Claims
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1. An adaptive one-bit audio digital-to-analog converter comprising
combining means receiving input dam pulses applied to the converter and signals from a negative feedback path for additively combining the input signals and the negative feedback path signals, and signal path means including a forward path receiving the output of said combining means and providing at its output the output of the converter and the input to the negative feedback path, and a negative feedback path coupling the output of said forward path to said combining means, said signal path means further including a variable gain amplifier and a filter having a fixed frequency-dependent response, said combining means and signal path means forming an adaptive low-pass filter having two regimes of operation, one in which the characteristic is that of a low-pass filter with a fixed cut-off frequency but with variable passband gain and another in which the characteristic is that of a low-pass filter with a variable cut-off frequency but a fixed passband gain.
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2. An adaptive one-bit audio analog-to-digital converter comprising
local decoder means, said local decoder means including combining means receiving input data pulses applied to the local decoder means and signals from a negative feedback path for additively combining the input signals and the negative feedback path signals, and signal path means including a forward path receiving the output of said combining means and providing at its output the output of the local decoder means and the input to the negative feedback path, and a negative feedback path coupling the output of said forward path to said combining means, said signal path means further including a variable gain amplifier and a filter having a fixed frequency-dependent response, said combining means and signal path means forming an adaptive low-pass filter having two regimes of operation, one in which the characteristic is that of a low-pass filter with a fixed cut-off frequency but with variable passband gain and another in which the characteristic is that of a low-pass filter with a variable cut-off frequency but a fixed passband gain, and means for comparing and sampling input analog signals with respect to signals from said local decoder means to provide output data pulses having a polarity (1 or 0) depending on whether the local decoder signal is positive or negative with respect to the input signal.
Specification