I need an A/D converter as cheap & fast as possible. I like AN513; it uses a
counter synchronized to a charging cap, which the input voltage is compared
to; A single slope converter.

I think the 768 uS conversion time could be shortened, by adding or
subtracting charge in microsecond binary-wieghted chunks
(.5,1,2,4,8,16,32,64) in a succesive-approximation style. Using a
binary-time wieghted exponential ramp switching and a comparator sampling
every 1 us for an 8-bit A/D conversion in under 10 us.

My first attempt at this has produced disapointing results- critical
adjustments of the RC time constants of an exponential ramp generator, which
is switched into an integrator (depending on data bit) resulted in D to A
generation with poor linearity & performance limited to 5 bits.

Anyone try that or have better problem fixes, better idea's & code?
Is it unrealistic to expect to be able to accurately integrate (with RC) the
8th time constant of a seperate RC network, for the least significant wieght
bit?
How good of a comparator is a PIC input? Is it affected by power supply
noise, output swiching/states, et?

Thanks.