Please Help...To convert Analog Signals to Quadrature Encoder signals

Hi All,

I have Hedenhain LS703 scales on a machine which I want to retrofit the
scales have analog output therefore I want to convert these into
Digital Quadrature signals . I have the Mariss'
AnalogOutputEncoderInterface.pdf from the yahoo files which converts
the Analog signals to A and B channels but don't understand how to
convert the the Index pulse.
Can anyone help in this regard , is there any other crcuit diagram
available for this conversion?

Are there any cheaper readymade converters available for this purpose.


Thanks

Babar