QAM encoder

Claim 2

An encoder for a QAM transmitter for transmitting a series of symbols, each symbol corresponding to a group of bits, comprising: a plurality of delay means through which said group of bits is delayed sequentially by a first period; an oscillator for generating a subaddress signal which is incremented periodically in accordance with a second period which is shorter than said first period; a plurality of look-up means corresponding to said delay means and having memory means, each of said look-up means receiving a delayed group of bits from a respective delay means and being provided for selecting a value from said memory means which corresponds to said delayed group of bits and said subaddress signal; and means for adding the value from each of said look-up means to produce said series of symbols.

Claim 3

The encoder of claim 1 wherein said first period is an integer multiple of said second period.

Claim 4

The encoder of claim 1 wherein said value is selected in accordance with the sum of said delayed group of bits and said subaddress signal.

Claim 5

The encoder of claim 3 wherein said sum corresponds to an angle and wherein said value is a product of the sine of said angle and a coefficient.

Claim 6

The encoder of claim 4 wherein said coefficient is equal to one of the coefficients of a digital transversal filter.

Claim 7

An encoder for encoding QAM-type nine-point symbols, comprising: a plurality first group of first delay units through which a group of data bits are propagated sequentially, each group corresponding to one of the QAM-type symbols; an oscillator having an output which is incremented periodically; a plurality of look-up circuits, corresponding to said delay units, each one comprising: a summer which adds the oscillator output to the output of the corresponding said first delay unit; a sign extractor which determines the sign of the sine of an angle which is equivalent to the summer output; a look-up table which determines a first quadrant equivalent to said angle; a memory means in which constants are stored and adapted to output one of said constants in accordance with the output of said look-up table and the oscillator output; and a master summer means which adds the memory means output of the look-up circuits.

Claim 8

An encoder for encoding QAM-type nine-point symbols, comprising: a plurality first group of first delay units through which a group of data bits are propagated sequentially, each group corresponding to one of the QAM-type symbols; an oscillator having an output which is incremented periodically; a plurality of look-up circuits, corresponding to said delay units, each one comprising: a summer which adds the oscillator output to the output of the corresponding said first delay unit; a sign extractor which determines the sign of the sine of an angle which is equivalent to the summer output; a look-up table which determines a first quadrant equivalent to said angle; a memory means in which constants are stored and adapted to output one of said constants in accordance with the output of said look-up table and the oscillator output; and a master summer means which adds the memory means output of the look-up circuits.

Claim 9

The encoder of claim 6 wherein said nine-point symbols include a silence symbol, and wherein said encoder includes a plurality of second delay units for propagating said silence symbol, each one of said second delay units being associated with a corresponding look-up circuit and adapted to disable a respective look-up circuit when a silence symbol is present.

Claim 10

The encoder of claim 6 wherein each said constant is the product of the sine of the angle equivalent and a coefficient.

Claim 11

The encoder of claim 8 wherein there are a first, second, third, and fourth look-up circuit and wherein said first period is six times larger than said second period.

Claim 12

The encoder of claim 9 wherein the coefficients of said first and fourth look-up circuits are a, b, c, d, e, and f, and the coefficients of the second and third look-up circuits are g, h, i, j, k, and l, where a, b, c, d, e, f, g, h, i, j, k and l are the coefficients of a 24-tap transversal digital filter.