circuit help: square and sin wave input = square wave output

hi,

i would like to ask what kind of circuit would produce such a response?

input:
- a sinewave with a varying amplitude directly proportional to the frequency. maximum pk is 3v and max freq is 500hz
- a square wave with a V-hi of 5V and V-low of 0V and a max freq of 500hz
- a square wave witha V-hi of 12V and a V-low of 0V and a max freq of 500Hz

output:
- a square wave that is ttl compatible (V-hi of 5v and V-low of 0V)
- the + side of the sine wave input must produce a high output (5v), while the - side of the sinewave must be low output
- the V-hi's of both square wave inputs must be a high output, while the V-low of the sqare wave inputs must produce a low output (0v)

what kind of circuit would produce such a response?

thanks!

3 input or gate and 1 comparator !

STEVE

ideally it would create such a waveform, but the problem arises when the amplitude of the sinewave goes below 1v....

is there a way to get rid of this?