A/D converter single-ended vs. differential

I have an A/D converter that will provide 11-bit resolution with single-ended inputs or 12-bit resolution for differential inputs. Is the extra bit in differential mode simply a sign bit or can I tie the "ground" of my signal to the negative of a differential input to get an extra bit of resolution? I suspect the answer is no, but it is worth asking anyway.

Thanks
Dale

What's the converter type and manufacturer?

Carl,
I've come across this situation in the past with various A/D interface boards and A/D converters integrated with SBCs but in this specific situation, the chip is a TI ADS7870. In the past I've always used single-ended inputs but have always been curious about the possibility of using differential inputs.
Thanks,
Dale

The differential input has less noise than single ended. For single ended, the noise is in the LSB range. With the diff amp, you reduce the noise and squeeze another bit of resolution.