FPGA Central

I am reading part of a book on this - basic stuff really. The
attenuation required so that any aliasing is less than the
quantisation error (r.m.s) voltage is given by

As>20Log10{max rms passband level/min rms stopband level}

where max rms passband level = A/sqrt(2)

min rms stopband level = sigma = A/( 2^B*sqrt(12) )

where B = no of bits. Here the author uses the dynamic range to be A
but I think it should be 2A ie from +A to -A. His formula works out to
be

As = 20log10(2^B*sqrt(6)) whereas I have 20log10(2^(B-1) * sqrt(6) )

similarly later he describes the rms quantisation error wrt unity
volts as


1/(2^B*sqrt(12)) and for the same reason I think this should be
2/(2^B*sqrt(12))

where have I gone wrong?


Thanks


Tom