You can se if the output bitstream represents the input signal correctly. To do this you only need and adder and a register to implement a simple accumulator. Assuming you are using a 1-bit quantizer, all you have to do is something lke this:
reg [15:0] accumulator;
if (reset) accumulator=0;
else begin
if (quantizer_output==1) accumulator = accumulator +1;
else accumulator = accumulator -1;
The accumulator will work as a very simple low pass filter. If you apply a sinusoidal signal to the input, the accumulator's output will be a sinusoid as well. This is the way I do and it works very well for me. This method does not work with square or triangular waves, only sine waves.
Hope it helped