Complex baseband envelope computation

The present invention pertains to an apparatus for and a method of determining an approximation of the envelope of a complex baseband signal having an in-phase component I and a quadrature component Q. More particularly, the present invention pertains to an apparatus for and a method of determining such envelope in a computationally efficient manner, permitting implementation in a gate array to provide high speed operation. An apparatus for and a method of determining the envelope of a complex baseband signal having an in-phase component I and a quadrature component Q by determining (I+Q) for sampled values of the baseband signal. The maximum and minimum values of I and Q are detected by detecting the larger of I and Q in a first detection circuit () and the smaller of I and Q in a second detection circuit (). A value x=½{(the detected minimum value)÷(the detected maximum value)}is calculated in a first calculation circuit (). The value of (I+Q) is then calculated based on the value of x. In a first embodiment the value of (I+Q) is calculated in a second calculation circuit () as the (the detected maximum value)×(1+x)/2+½(1+x−x+x−x+x−x). In a second embodiment, the value of (I+Q) is calculated in a second calculation circuit () as (the detected maximum value)×(1+2x+x/2)÷(1+x). Preferably, the apparatus is implemented in a gate array, such as a field programmable gate array, providing high speed operation.