Automatic bias circuit
First Claim
1. An automatic bias control circuit for a synchronous data detector in which the baseline of a data signal input to the automatic bias control circuit is approximated by a bias level, said automatic bias control circuit comprising:
- means responsive to the input data signal and said bias level for producing binary data levels, and signals representing data level transition edges;
means for generating local clock signals;
means for detecting a time relationship between said level transition edge representative signals and at least one of said local clock signals; and
means for modifying the bias level in accordance with said detected time relationship thereby causing said data level transition edges to be substantially synchronized with said local clock signals.
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Abstract
An automatic bias control circuit for a data limiter in a synchronous data communications system is disclosed. After word synchronization is achieved, the automatic bias control circuit is enabled and a time relationship between the limited data signal edges and a synchronized local clock signal is detected. The automatically controlled bias level is then modified upward or downward by an additive or subtractive voltage increment for a period of time related to the data bit rate so that the true baseline of the data signal is approximated by the bias level and the detected time relationship is thereby adjusted so that the edges are essentially synchronized with the local clock signal.
73 Citations
18 Claims
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1. An automatic bias control circuit for a synchronous data detector in which the baseline of a data signal input to the automatic bias control circuit is approximated by a bias level, said automatic bias control circuit comprising:
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means responsive to the input data signal and said bias level for producing binary data levels, and signals representing data level transition edges; means for generating local clock signals; means for detecting a time relationship between said level transition edge representative signals and at least one of said local clock signals; and means for modifying the bias level in accordance with said detected time relationship thereby causing said data level transition edges to be substantially synchronized with said local clock signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A bias contro1 circuit for a data signal limiter of a synchronous data decoder in a radio data communications system in which the baseline wander of the data signal is compensated by a variable bias level, comprising:
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means for detecting a predetermined binary pattern in the data signal; means for establishing a bias level magnitude dependent upon the average magnitude of the data signal; means for disabling said bias level magnitude establishing means when said predetermined binary pattern is detected; means responsive to said bias level magnitude for limiting the data signal to produce binary data levels, related to the data signals and to produce signals representing data level transition edges; means for generating local clock signals synchronized with the data signal no later than the occurrence of said detection of said predetermined binary pattern; means for detecting a time relationship between said level transition edge representative signals and at least one local clock signal; and means for modifying said bias level magnitude incrementally in a positive direction each time said time relationship detection indicates a bias level less than the baseline and for modifying said bias level magnitude incrementally in a negative direction each time said time relationship detection indicates a bias level greater than the baseline. - View Dependent Claims (10, 11, 12, 13)
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14. A method of biasing a data signal limiter of a synchronous data decoder to compensate baseline wander of the data signal with a bias level, comprising the steps of:
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producing binary data levels and signals representing data level transition edges in response to the data signal and said bias level; generating local clock signals; detecting a time relationship between said level transition edge representative signals and at least one of said local clock signals; and modifying the bias level in accordance with said detected time relationship, thereby causing said data level transition edges to be substantially synchronized with said local clock signals. - View Dependent Claims (15, 16, 17, 18)
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Specification