Circuitry for calculating magnitude of vector sum from its orthogonal components in digital television receiver

Apparatus for generating the magnitude value of the vector sum of a pair of quadrature-related component vectors comprising:

• means for receiving the magnitude values I and Q of said pair of quadrature-related component vectors;
• means for generating an associated pair of logarithmic values Log.sub.B .vertline.I.vertline. and Log.sub.B .vertline.Q.vertline. to a base B;
• means for calculating the absolute value .vertline.D.vertline. of the difference between said logarithmic values Log.sub.B .vertline.I.vertline. and Log.sub.B .vertline.Q.vertline.;
• means for generating a correction value F(.vertline.D.vertline.) equal to 0.5 Log.sub.B (1+B.sup.-2.vertline.D.vertline.);
• means including means for determining the larger of said logarithmic values Log.sub.B .vertline.I.vertline. and Log.sub.B .vertline.Q.vertline., and for adding the correction value to the larger of the logarithmic values Log.sub.B .vertline.I.vertline. and Log.sub.B .vertline.Q.vertline.;
• and
• means for producing the antilog of the sum of the correction value and the larger of the logarithmic values Log.sub.B .vertline.I.vertline. and Log.sub.B .vertline.Q.vertline., to generate a value C substantially equal to the magnitude of the vector sum of said quadrature-related component vectors.