Implementation of a DTMF Receiver in VHDL


        A DTMF (Dual Tone Multi-Frequency) receiver decodes 
signals generated by a telephone's touch-tone keypad to determine 
the key pressed.  The input signals are processed by filters, 
rectifiers and threshold detectors to produce an output of 1's 
or 0's.  The outputs can be encoded to give the inputted key.  
My main focus is on implementing and optimizing second order 
digital filters used in the receiver.  These second order
digital filters can be cascaded to create fourth order digital 
filters.  The whole DTMF system is also implemented.  This 
involves describing each component in VHDL(VHSI--Very High 
Speed Integrated Circuit--Hardware Description Language) and 
optimizing the design for less area.  The DTMF receiver
described in VHDL is put together and tested for comparison 
with implementations in other hardware description languages 
to determine speed and cost efficiency.